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Group Design

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  Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-07 18:46 -0700
    Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-07 19:02 -0700
      Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-07 20:36 -0700
        Re: Group Design David Brown <david.brown@hesbynett.no> - 2020-07-08 09:31 +0200
          Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 07:08 -0700
    Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-08 14:13 +0200
      Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 07:19 -0700
        Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-08 18:57 +0200
          Re: Group Design Theo <theom+news@chiark.greenend.org.uk> - 2020-07-08 18:28 +0100
          Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 11:12 -0700
            Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-08 23:34 +0200
              Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-08 15:20 -0700
                Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-08 23:00 -0700
                Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-10 10:09 +0200
                Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-07 00:01 +0100
                  Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-06 17:37 -0700
                    Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-08-07 03:06 -0700
                  Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-06 21:50 -0400
                    Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-06 19:12 -0700
                      Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-06 22:27 -0400
                        Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-06 19:36 -0700
                          Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-06 23:39 -0400
                    Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-07 12:30 +0100
                      Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-07 09:57 -0400
                        Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-08 00:37 +0100
                          Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-07 20:29 -0400
                          Re: Group Design upsidedown@downunder.com - 2020-08-08 08:59 +0300
                          Re: Group Design David Brown <david.brown@hesbynett.no> - 2020-08-10 15:43 +0200
                            Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-10 09:18 -0700
                      Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 07:12 -0700
                        Re: Group Design Chris <xxx.syseng.yyy@gfsys.co.uk> - 2020-08-08 00:00 +0100
                          Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-08-07 20:30 -0400
                            Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 17:57 -0700
                          Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 17:56 -0700
                        Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-08-07 18:10 -0700
                          Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 19:43 -0700
                      Re: Group Design Dimiter_Popoff <dp@tgi-sci.com> - 2020-08-07 20:42 +0300
                        Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-08-07 13:48 -0700
        Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-08 14:11 -0700
        Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-07-09 04:25 -0400
          Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 11:37 -0700
            Re: Group Design Paul Rubin <no.email@nospam.invalid> - 2020-07-09 11:54 -0700
            Re: Group Design Tom Gardner <spamjunk@blueyonder.co.uk> - 2020-07-09 20:02 +0100
            Re: Group Design Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2020-07-09 15:31 -0400
              Re: Group Design lasselangwadtchristensen@gmail.com - 2020-07-09 15:36 -0700
                Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 18:36 -0700
                  Re: Group Design Clifford Heath <no.spam@please.net> - 2020-07-10 16:17 +1000
                    Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 23:36 -0700
                      Re: Group Design Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2020-07-10 10:22 +0200
        Re: Group Design David Brown <david.brown@hesbynett.no> - 2020-07-09 14:40 +0200
    Re: Group Design John Speth <johnspeth@yahoo.com> - 2020-07-09 07:59 -0700
    Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-09 18:33 -0700
      Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 19:01 -0700
        Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-09 22:32 -0700
        Re: Group Design George Neuner <gneuner2@comcast.net> - 2020-07-10 17:36 -0400
          Re: Group Design Ed Prochak <edprochak@gmail.com> - 2020-07-14 11:09 -0700
            Re: Group Design George Neuner <gneuner2@comcast.net> - 2020-07-16 00:26 -0400
    Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-09 22:48 -0700
      Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-09 23:53 -0700
        Re: Group Design Rick C <gnuarm.deletethisbit@gmail.com> - 2020-07-10 01:15 -0700
          Re: Group Design Don Y <blockedofcourse@foo.invalid> - 2020-07-10 02:22 -0700

Page 2 of 4 — ← Prev page 1 [2] 3 4  Next page →

#29916

On Thursday, August 6, 2020 at 10:27:27 PM UTC-4, Phil Hobbs wrote:
> On 2020-08-06 22:12, Rick C wrote:
> > On Thursday, August 6, 2020 at 9:50:24 PM UTC-4, Phil Hobbs wrote:
> >> On 2020-08-06 19:01, Chris wrote:
> >>> On 07/08/20 23:20, Rick C wrote:
> >>>
> >>>> I'm also concerned about the board layout.  The board is not at all
> >>>> dense but there are several
> >>>
> >>> parts that need copper area for heat sinking.  They are using a linear
> >>> regulator to drop 12+ volts
> >>>
> >>> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!  So the 5V
> >>> regulator gets quite warm,
> >>>
> >>> 70°C!!!
> >>>
> >>> You should be concerned. The whole thing about safety critical kit is
> >>> that it should be conservatively designed, with all parts running well
> >>> within their ratings. If the hw bod is happy with a regulator running
> >>> at 70c, he must be clueless. Sorry, but it needs to be said.
> >>>
> >>> If you care about your professional career and any litigation
> >>> issues, you should either have enough influence on the project
> >>> direction to stop design errors like that, or just walk away from it...
> >>>
> >>> Chris
> >>
> >> Hmm, interesting.  Most linear regulators I'm familiar with are rated to
> >> 125 C junction temperature, and some higher.  What safety or regulatory
> >> issues have you run into that were caused by running some part 55C below
> >> its rated temperature?
> > 
> > That was the case temp via an IR gun.  So the die was hotter.  I would not approve a design with a part running so hot.  I believe the failure rate goes up quite quickly with temp.  The real point is this is because the layout was not correct using thermal breaks around the thermal pad!!!  Easy enough to fix lowering the temp probably by 30 °C.
> > 
> > Did you not read the original post about this?
> > 
> 
> I've designed a fair bit of stuff to work in ambients higher than that, 
> from remote satcom stuff to downhole instruments running at 175C.

So???  Higher temps means shorter life.  Is that a false statement?  

There is also the issue of heating up things adjacent to the hot part and at 70 °C there is risk of burning someone not used to board getting that hot.  

In other words, there is no reason to have such an abortion for a design that it gets so hot.  Why is this an issue for you?  You are not making any sense at all. 


> The amateur vent stuff is all March 2020 at this point, so I'm 
> interested in the broader context.

What broader context??? 

-- 

  Rick C.

  ---- Get 1,000 miles of free Supercharging
  ---- Tesla referral code - https://ts.la/richard11209

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#29917

On 2020-08-06 22:36, Rick C wrote:
> On Thursday, August 6, 2020 at 10:27:27 PM UTC-4, Phil Hobbs wrote:
>> On 2020-08-06 22:12, Rick C wrote:
>>> On Thursday, August 6, 2020 at 9:50:24 PM UTC-4, Phil Hobbs
>>> wrote:
>>>> On 2020-08-06 19:01, Chris wrote:
>>>>> On 07/08/20 23:20, Rick C wrote:
>>>>> 
>>>>>> I'm also concerned about the board layout.  The board is
>>>>>> not at all dense but there are several
>>>>> 
>>>>> parts that need copper area for heat sinking.  They are using
>>>>> a linear regulator to drop 12+ volts
>>>>> 
>>>>> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!
>>>>> So the 5V regulator gets quite warm,
>>>>> 
>>>>> 70°C!!!
>>>>> 
>>>>> You should be concerned. The whole thing about safety
>>>>> critical kit is that it should be conservatively designed,
>>>>> with all parts running well within their ratings. If the hw
>>>>> bod is happy with a regulator running at 70c, he must be
>>>>> clueless. Sorry, but it needs to be said.
>>>>> 
>>>>> If you care about your professional career and any
>>>>> litigation issues, you should either have enough influence on
>>>>> the project direction to stop design errors like that, or
>>>>> just walk away from it...
>>>>> 
>>>>> Chris
>>>> 
>>>> Hmm, interesting.  Most linear regulators I'm familiar with are
>>>> rated to 125 C junction temperature, and some higher.  What
>>>> safety or regulatory issues have you run into that were caused
>>>> by running some part 55C below its rated temperature?
>>> 
>>> That was the case temp via an IR gun.  So the die was hotter.  I
>>> would not approve a design with a part running so hot.  I believe
>>> the failure rate goes up quite quickly with temp.  The real point
>>> is this is because the layout was not correct using thermal
>>> breaks around the thermal pad!!!  Easy enough to fix lowering the
>>> temp probably by 30 °C.
>>> 
>>> Did you not read the original post about this?
>>> 
>> 
>> I've designed a fair bit of stuff to work in ambients higher than
>> that, from remote satcom stuff to downhole instruments running at
>> 175C.
> 
> So???  Higher temps means shorter life.  Is that a false statement?
> 
> There is also the issue of heating up things adjacent to the hot part
> and at 70 °C there is risk of burning someone not used to board
> getting that hot.
> 
> In other words, there is no reason to have such an abortion for a
> design that it gets so hot.  Why is this an issue for you?  You are
> not making any sense at all.

Okay, so you've got zilch.  No worries.

Cheers

Phil Hobbs


-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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#29919

On 08/07/20 02:50, Phil Hobbs wrote:
> On 2020-08-06 19:01, Chris wrote:
>> On 07/08/20 23:20, Rick C wrote:
>>
>>> I'm also concerned about the board layout.  The board is not at all
>>> dense but there are several
>>
>> parts that need copper area for heat sinking.  They are using a linear
>> regulator to drop 12+ volts
>>
>> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!  So the 5V
>> regulator gets quite warm,
>>
>> 70°C!!!
>>
>> You should be concerned. The whole thing about safety critical kit is
>> that it should be conservatively designed, with all parts running well
>> within their ratings. If the hw bod is happy with a regulator running
>> at 70c, he must be clueless. Sorry, but it needs to be said.
>>
>> If you care about your professional career and any litigation
>> issues, you should either have enough influence on the project
>> direction to stop design errors like that, or just walk away from it...
>>
>> Chris
>
> Hmm, interesting. Most linear regulators I'm familiar with are rated to
> 125 C junction temperature, and some higher. What safety or regulatory
> issues have you run into that were caused by running some part 55C below
> its rated temperature?
>
> Cheers
>
> Phil Hobbs
>

That's not the point and reliability is affected by temperature. It may
not matter for a short lived down hole item where failure has no safety
implications, but not good enough otherwise. The constant temperature
cycling will affect wire bonds and reliability. Cheap tacky design,
using a linear regulator to go from 12v to 5, then 3.3, considerable
current, where a point of use switcher would be a far more efficient and
probably more reliable solution as well Wasted power needs a bigger 
backup battery etc...

Chris

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#29920

On 2020-08-07 07:30, Chris wrote:
> On 08/07/20 02:50, Phil Hobbs wrote:
>> On 2020-08-06 19:01, Chris wrote:
>>> On 07/08/20 23:20, Rick C wrote:
>>> 
>>>> I'm also concerned about the board layout.  The board is not at
>>>> all dense but there are several
>>> 
>>> parts that need copper area for heat sinking.  They are using a
>>> linear regulator to drop 12+ volts
>>> 
>>> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!  So
>>> the 5V regulator gets quite warm,
>>> 
>>> 70°C!!!
>>> 
>>> You should be concerned. The whole thing about safety critical
>>> kit is that it should be conservatively designed, with all parts
>>> running well within their ratings. If the hw bod is happy with a
>>> regulator running at 70c, he must be clueless. Sorry, but it
>>> needs to be said.
>>> 
>>> If you care about your professional career and any litigation 
>>> issues, you should either have enough influence on the project 
>>> direction to stop design errors like that, or just walk away from
>>> it...
>>> 
>>> Chris
>> 
>> Hmm, interesting. Most linear regulators I'm familiar with are
>> rated to 125 C junction temperature, and some higher. What safety
>> or regulatory issues have you run into that were caused by running
>> some part 55C below its rated temperature?
>> 
>> Cheers
>> 
>> Phil Hobbs
>> 
> 
> That's not the point

Not yours, I gather, but it is mine.  I'm not being argumentative, I 
just want to know if there's good reliability data out there that I 
should know about.  Opinions can be useful too, if they're at least 
based on detailed anecdotes.

> and reliability is affected by temperature. It
> may not matter for a short lived down hole item where failure has no
> safety implications, but not good enough otherwise. The constant
> temperature cycling will affect wire bonds and reliability.

So we're told by MIL-HDBK-217, based on a famously flawed methodology 
(removing parts always improves reliability), invalid statistical 
assumptions (Arrhenius scaling of failure rates over large temperature 
ranges), and data from the 1960s iirc.  Is there actual data to support 
that with modern components?

> Cheap tacky design, using a linear regulator to go from 12v to 5,
> then 3.3, considerable current, where a point of use switcher would
> be a far more efficient and probably more reliable solution as well
> Wasted power needs a bigger backup battery etc...

I know it isn't what the cool kids do, but that doesn't make it 
unreliable or cause it to fail safety inspections AFAICT.  Medical may 
be different, but it would pass UL with no issues.  What regulations 
nwould you expect it to fall foul of?

Cheers

Phil Hobbs


> 
-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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#29926

On 08/07/20 14:57, Phil Hobbs wrote:

> I know it isn't what the cool kids do, but that doesn't make it
> unreliable or cause it to fail safety inspections AFAICT. Medical may be
> different, but it would pass UL with no issues. What regulations nwould
> you expect it to fall foul of?
>
> Cheers
>
> Phil Hobbs
>

It's not the regulations, as afaics approvals are more concerned with
*process*, how the design decisons were made and why. Would not
necessarily catch design errors that resulted in a regulator running
near it's design limit, though avionics or mil temperature cycle
testing might  cause a failure because of lack of margin for a device.

Whatever you might think, it's well known that high temperatures and
cycling shortens the life of electronics and no, I don't have
references,but it's all on the web. Some prefer to skimp every penny,
others prefer conservative design rules. It's the difference between
consumer electronics and pro kit. may look like the same parts, but
the design tradeoffs are different. Engineering design is always an
approximation and compromise: performance, cost, reliability, pick any
two...

Chris

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#29927

On 2020-08-07 19:37, Chris wrote:
> On 08/07/20 14:57, Phil Hobbs wrote:
> 
>> I know it isn't what the cool kids do, but that doesn't make it
>> unreliable or cause it to fail safety inspections AFAICT. Medical may be
>> different, but it would pass UL with no issues. What regulations nwould
>> you expect it to fall foul of?
>>
>> Cheers
>>
>> Phil Hobbs
>>
> 
> It's not the regulations, as afaics approvals are more concerned with
> *process*, how the design decisons were made and why. Would not
> necessarily catch design errors that resulted in a regulator running
> near it's design limit, though avionics or mil temperature cycle
> testing might  cause a failure because of lack of margin for a device.
> 
> Whatever you might think, it's well known that high temperatures and
> cycling shortens the life of electronics and no, I don't have
> references,but it's all on the web. Some prefer to skimp every penny,
> others prefer conservative design rules. It's the difference between
> consumer electronics and pro kit. may look like the same parts, but
> the design tradeoffs are different. Engineering design is always an
> approximation and compromise: performance, cost, reliability, pick any
> two...
> 
> Chris

Okay, so you don't have anything either.  No worries, thanks.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[toc] | [prev] | [next] | [standalone]

#29935

On Sat, 08 Aug 2020 00:37:35 +0100, Chris <xxx.syseng.yyy@gfsys.co.uk>
wrote:

>On 08/07/20 14:57, Phil Hobbs wrote:
>
>> I know it isn't what the cool kids do, but that doesn't make it
>> unreliable or cause it to fail safety inspections AFAICT. Medical may be
>> different, but it would pass UL with no issues. What regulations nwould
>> you expect it to fall foul of?
>>
>> Cheers
>>
>> Phil Hobbs
>>
>
>It's not the regulations, as afaics approvals are more concerned with
>*process*, how the design decisons were made and why. Would not
>necessarily catch design errors that resulted in a regulator running
>near it's design limit, though avionics or mil temperature cycle
>testing might  cause a failure because of lack of margin for a device.

At what ambient temperature and air pressure was that +70 C case
temperature taken ? At +20 C and sea level ?

If the product is aimed for the international market, people live in
over +40 C temperatures and some at over 4 km altitude. With
convection cooling, the case (and junction temperature) is
proportional to ambient temperature.

At higher altitudes, the air pressure and density is lower, thus a
higher air flow (fan ?) us required to restore the mass flow and thus
heat removal at a specific delta-T.

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#29948

On 08/08/2020 01:37, Chris wrote:
> On 08/07/20 14:57, Phil Hobbs wrote:
> 
>> I know it isn't what the cool kids do, but that doesn't make it
>> unreliable or cause it to fail safety inspections AFAICT. Medical may be
>> different, but it would pass UL with no issues. What regulations nwould
>> you expect it to fall foul of?
>>
>> Cheers
>>
>> Phil Hobbs
>>
> 
> It's not the regulations, as afaics approvals are more concerned with
> *process*, how the design decisons were made and why. Would not
> necessarily catch design errors that resulted in a regulator running
> near it's design limit, though avionics or mil temperature cycle
> testing might  cause a failure because of lack of margin for a device.
> 
> Whatever you might think, it's well known that high temperatures and
> cycling shortens the life of electronics and no, I don't have
> references,but it's all on the web. Some prefer to skimp every penny,
> others prefer conservative design rules. It's the difference between
> consumer electronics and pro kit. may look like the same parts, but
> the design tradeoffs are different. Engineering design is always an
> approximation and compromise: performance, cost, reliability, pick any
> two...
> 
> Chris
> 

I think it's fair to say that this 70 C case with poor thermal contact 
with the board is an indicator of bad design - bad schematic design 
(using a linear regulator rather than a switch mode), and bad layout 
design (poor cooling).  And poor design in such an obvious case suggests 
poor design overall - which is not going to go well for any kind of 
safety requirements or regulations where the design process is considered.

It is also correct to say that the reliability of a system is a function 
of the reliability of all the parts, and that high temperatures and 
temperature cycling shorten lifetimes and increase the rate of failures. 
  But you can't say how significant this particular part would be 
without a lot more information about the rest of the system.  As Phil 
says, a part rated for 125 C is not going to see much increased failure 
risk at 70 C compared to 50 C.  But if it sits next to a part that is 
rated to 85 C and the final system is mounted in a closed box and used 
in the Qatar summer, perhaps it will have a relevant effect.

All in all, this looks like a rush job put together by people with no 
experience with high reliability or safety-related systems.  That's the 
general problem, rather than one particular hot regulator.

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#29949

On Monday, August 10, 2020 at 9:43:06 AM UTC-4, David Brown wrote:
> On 08/08/2020 01:37, Chris wrote:
> > On 08/07/20 14:57, Phil Hobbs wrote:
> > 
> >> I know it isn't what the cool kids do, but that doesn't make it
> >> unreliable or cause it to fail safety inspections AFAICT. Medical may be
> >> different, but it would pass UL with no issues. What regulations nwould
> >> you expect it to fall foul of?
> >>
> >> Cheers
> >>
> >> Phil Hobbs
> >>
> > 
> > It's not the regulations, as afaics approvals are more concerned with
> > *process*, how the design decisons were made and why. Would not
> > necessarily catch design errors that resulted in a regulator running
> > near it's design limit, though avionics or mil temperature cycle
> > testing might  cause a failure because of lack of margin for a device.
> > 
> > Whatever you might think, it's well known that high temperatures and
> > cycling shortens the life of electronics and no, I don't have
> > references,but it's all on the web. Some prefer to skimp every penny,
> > others prefer conservative design rules. It's the difference between
> > consumer electronics and pro kit. may look like the same parts, but
> > the design tradeoffs are different. Engineering design is always an
> > approximation and compromise: performance, cost, reliability, pick any
> > two...
> > 
> > Chris
> > 
> 
> I think it's fair to say that this 70 C case with poor thermal contact 
> with the board is an indicator of bad design - bad schematic design 
> (using a linear regulator rather than a switch mode), and bad layout 
> design (poor cooling).  And poor design in such an obvious case suggests 
> poor design overall - which is not going to go well for any kind of 
> safety requirements or regulations where the design process is considered.

But you're not judging, right? 

No one supports the use of a switching regulator... well, until I did a power budget.  Seems that the two LCD displays use some 10x the power of the rest of the circuit ex motor.  With the motor using 2 amps at some duty cycle the LCD displays appear to be more of a drain on the battery.  We are looking at the issue now.  Even with a switcher the savings is only 50% of the LCD power.  

Personally I think LCDs suck with a contrast ratio of 3:1, but the rest of the world seems to like them. 


> It is also correct to say that the reliability of a system is a function 
> of the reliability of all the parts, and that high temperatures and 
> temperature cycling shorten lifetimes and increase the rate of failures. 
>   But you can't say how significant this particular part would be 
> without a lot more information about the rest of the system.  As Phil 
> says, a part rated for 125 C is not going to see much increased failure 
> risk at 70 C compared to 50 C.  But if it sits next to a part that is 
> rated to 85 C and the final system is mounted in a closed box and used 
> in the Qatar summer, perhaps it will have a relevant effect.
> 
> All in all, this looks like a rush job put together by people with no 
> experience with high reliability or safety-related systems.  That's the 
> general problem, rather than one particular hot regulator.

That's certainly true.  The other day I was in a conference call with the project lead and the new requirements guy.  The requirements are more of a list than anything formally analyzed.  The ultimate reason for this seems to be the realization of the large amounts of personal time being invested in the project and in particular the time invested by the project lead.  

For me the project is recreation during the pandemic isolation.  For others it competes for their free time against families, etc.  That doesn't change the fact that to do the job right requires using the proper tools and methods. 

I am nearing my bail out point.  I'd like to get through a design review of the schematic and the layout.  Then I'm happy to go. 

-- 

  Rick C.

  -++- Get 1,000 miles of free Supercharging
  -++- Tesla referral code - https://ts.la/richard11209

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#29921

On Friday, August 7, 2020 at 7:30:44 AM UTC-4, Chris wrote:
> On 08/07/20 02:50, Phil Hobbs wrote:
> > On 2020-08-06 19:01, Chris wrote:
> >> On 07/08/20 23:20, Rick C wrote:
> >>
> >>> I'm also concerned about the board layout.  The board is not at all
> >>> dense but there are several
> >>
> >> parts that need copper area for heat sinking.  They are using a linear
> >> regulator to drop 12+ volts
> >>
> >> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!  So the 5V
> >> regulator gets quite warm,
> >>
> >> 70°C!!!
> >>
> >> You should be concerned. The whole thing about safety critical kit is
> >> that it should be conservatively designed, with all parts running well
> >> within their ratings. If the hw bod is happy with a regulator running
> >> at 70c, he must be clueless. Sorry, but it needs to be said.
> >>
> >> If you care about your professional career and any litigation
> >> issues, you should either have enough influence on the project
> >> direction to stop design errors like that, or just walk away from it...
> >>
> >> Chris
> >
> > Hmm, interesting. Most linear regulators I'm familiar with are rated to
> > 125 C junction temperature, and some higher. What safety or regulatory
> > issues have you run into that were caused by running some part 55C below
> > its rated temperature?
> >
> > Cheers
> >
> > Phil Hobbs
> >
> 
> That's not the point and reliability is affected by temperature. It may
> not matter for a short lived down hole item where failure has no safety
> implications, but not good enough otherwise. The constant temperature
> cycling will affect wire bonds and reliability. Cheap tacky design,
> using a linear regulator to go from 12v to 5, then 3.3, considerable
> current, where a point of use switcher would be a far more efficient and
> probably more reliable solution as well Wasted power needs a bigger 
> backup battery etc...

Efficiency may be personally important to an engineer who wants to overdesign everything, but this device has a 2 amp motor running off the 15 volts and it is all line powered, so no need to squeeze every last joule out of the design.  We are measuring some low level signals that could easily be disrupted by the switching currents.  So adding that type of a noise source would only be done if actually required. 

Oddly enough most of the power used in the electronics other than the motor are in the LED back lights for the low power LCD displays.  I have thought of using a switcher for them, but even at the 250 mA power level it's just not worth the hassle of dealing with the noise.  

Hmmm...  maybe that is a bigger impact than anyone here is thinking.  The display is on all the time.  The motor only runs at high power about half the time.  So it's really more like 1 amp.  Now the ratio is more like 4:1.  We don't have good data on the motor current, so no one has paid attention to the battery time.  

There are so many holes in this net.  lol 

BTW, does anyone understand what Phil Hobbs is going on about???  Why does he talk in code? 

-- 

  Rick C.

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#29925

On 08/07/20 15:12, Rick C wrote:
>

> Efficiency may be personally important to an engineer who wants to overdesign everything, but this device has a 2 amp motor running off the 15 volts and it is all line powered, so no need to squeeze every last joule out of the design.  We are measuring some low level signals that could easily be disrupted by the switching currents.  So adding that type of a noise source would only be done if actually required.
>
> Oddly enough most of the power used in the electronics other than the motor are in the LED back lights for the low power LCD displays.  I have thought of using a switcher for them, but even at the 250 mA power level it's just not worth the hassle of dealing with the noise.
>
> Hmmm...  maybe that is a bigger impact than anyone here is thinking.  The display is on all the time.  The motor only runs at high power about half the time.  So it's really more like 1 amp.  Now the ratio is more like 4:1.  We don't have good data on the motor current, so no one has paid attention to the battery time.
>
> There are so many holes in this net.  lol
>
> BTW, does anyone understand what Phil Hobbs is going on about???  Why does he talk in code?
>

If you are switching a 2 amp motor load, then you already have more
problems than a point of use regulator, in terms of supply load step
function. If it's a dc brush motor, perhaps permanent magnet, that
looks like little more than 0 ohms, or nearly a short circuit at rest,
so you will need to ramp that up to limit current. Once spun up,
power is more or less proportional to load, but unless the data
sheet has all the info, you will need to build a mechanical test rig
to define the motor characteristics. I would do that anyway, to get
a idea of what size motor is needed and optimise the circuit
to drive it.

There's quite range of ic's for motor control, with soft start,
current limiting etc. You could perhaps use a brushless moter and
again, some ic choice on how that's done. Advantage is zero
commutator noise to upset other things. You really can't just use a
relay to switch that motor.

 > BTW, does anyone understand what Phil Hobbs is going on about???
   Why does he talk in code?

Iirc, if he will excuse the comment, Phil is a scientist, Science is
about math and numbers, measurement accuracy, whereas electronics,
once you get the theory  under the belt, as more about experience,
knowing what works, what doesn't and not a little intuition...

Chris

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#29928

On 2020-08-07 19:00, Chris wrote:
> On 08/07/20 15:12, Rick C wrote:
>>
> 
>> Efficiency may be personally important to an engineer who wants to 
>> overdesign everything, but this device has a 2 amp motor running off 
>> the 15 volts and it is all line powered, so no need to squeeze every 
>> last joule out of the design.  We are measuring some low level signals 
>> that could easily be disrupted by the switching currents.  So adding 
>> that type of a noise source would only be done if actually required.
>>
>> Oddly enough most of the power used in the electronics other than the 
>> motor are in the LED back lights for the low power LCD displays.  I 
>> have thought of using a switcher for them, but even at the 250 mA 
>> power level it's just not worth the hassle of dealing with the noise.
>>
>> Hmmm...  maybe that is a bigger impact than anyone here is thinking.  
>> The display is on all the time.  The motor only runs at high power 
>> about half the time.  So it's really more like 1 amp.  Now the ratio 
>> is more like 4:1.  We don't have good data on the motor current, so no 
>> one has paid attention to the battery time.
>>
>> There are so many holes in this net.  lol
>>
>> BTW, does anyone understand what Phil Hobbs is going on about???  Why 
>> does he talk in code?
>>
> 
> If you are switching a 2 amp motor load, then you already have more
> problems than a point of use regulator, in terms of supply load step
> function. If it's a dc brush motor, perhaps permanent magnet, that
> looks like little more than 0 ohms, or nearly a short circuit at rest,
> so you will need to ramp that up to limit current. Once spun up,
> power is more or less proportional to load, but unless the data
> sheet has all the info, you will need to build a mechanical test rig
> to define the motor characteristics. I would do that anyway, to get
> a idea of what size motor is needed and optimise the circuit
> to drive it.
> 
> There's quite range of ic's for motor control, with soft start,
> current limiting etc. You could perhaps use a brushless moter and
> again, some ic choice on how that's done. Advantage is zero
> commutator noise to upset other things. You really can't just use a
> relay to switch that motor.
> 
>  > BTW, does anyone understand what Phil Hobbs is going on about???
>    Why does he talk in code?
> 
> Iirc, if he will excuse the comment, Phil is a scientist, Science is
> about math and numbers, measurement accuracy, whereas electronics,
> once you get the theory  under the belt, as more about experience,
> knowing what works, what doesn't and not a little intuition...
> 
> Chris
> 

I've been an electronics designer for a decade longer than I've been a 
scientist.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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#29931

On Friday, August 7, 2020 at 8:30:17 PM UTC-4, Phil Hobbs wrote:
> On 2020-08-07 19:00, Chris wrote:
> > On 08/07/20 15:12, Rick C wrote:
> >>
> > 
> >> Efficiency may be personally important to an engineer who wants to 
> >> overdesign everything, but this device has a 2 amp motor running off 
> >> the 15 volts and it is all line powered, so no need to squeeze every 
> >> last joule out of the design.  We are measuring some low level signals 
> >> that could easily be disrupted by the switching currents.  So adding 
> >> that type of a noise source would only be done if actually required.
> >>
> >> Oddly enough most of the power used in the electronics other than the 
> >> motor are in the LED back lights for the low power LCD displays.  I 
> >> have thought of using a switcher for them, but even at the 250 mA 
> >> power level it's just not worth the hassle of dealing with the noise.
> >>
> >> Hmmm...  maybe that is a bigger impact than anyone here is thinking.  
> >> The display is on all the time.  The motor only runs at high power 
> >> about half the time.  So it's really more like 1 amp.  Now the ratio 
> >> is more like 4:1.  We don't have good data on the motor current, so no 
> >> one has paid attention to the battery time.
> >>
> >> There are so many holes in this net.  lol
> >>
> >> BTW, does anyone understand what Phil Hobbs is going on about???  Why 
> >> does he talk in code?
> >>
> > 
> > If you are switching a 2 amp motor load, then you already have more
> > problems than a point of use regulator, in terms of supply load step
> > function. If it's a dc brush motor, perhaps permanent magnet, that
> > looks like little more than 0 ohms, or nearly a short circuit at rest,
> > so you will need to ramp that up to limit current. Once spun up,
> > power is more or less proportional to load, but unless the data
> > sheet has all the info, you will need to build a mechanical test rig
> > to define the motor characteristics. I would do that anyway, to get
> > a idea of what size motor is needed and optimise the circuit
> > to drive it.
> > 
> > There's quite range of ic's for motor control, with soft start,
> > current limiting etc. You could perhaps use a brushless moter and
> > again, some ic choice on how that's done. Advantage is zero
> > commutator noise to upset other things. You really can't just use a
> > relay to switch that motor.
> > 
> >  > BTW, does anyone understand what Phil Hobbs is going on about???
> >    Why does he talk in code?
> > 
> > Iirc, if he will excuse the comment, Phil is a scientist, Science is
> > about math and numbers, measurement accuracy, whereas electronics,
> > once you get the theory  under the belt, as more about experience,
> > knowing what works, what doesn't and not a little intuition...
> > 
> > Chris
> > 
> 
> I've been an electronics designer for a decade longer than I've been a 
> scientist.

And yet you still don't understand anything we are talking about.  

-- 

  Rick C.

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#29930

On Friday, August 7, 2020 at 7:00:47 PM UTC-4, Chris wrote:
> On 08/07/20 15:12, Rick C wrote:
> >
> 
> > Efficiency may be personally important to an engineer who wants to overdesign everything, but this device has a 2 amp motor running off the 15 volts and it is all line powered, so no need to squeeze every last joule out of the design.  We are measuring some low level signals that could easily be disrupted by the switching currents.  So adding that type of a noise source would only be done if actually required.
> >
> > Oddly enough most of the power used in the electronics other than the motor are in the LED back lights for the low power LCD displays.  I have thought of using a switcher for them, but even at the 250 mA power level it's just not worth the hassle of dealing with the noise.
> >
> > Hmmm...  maybe that is a bigger impact than anyone here is thinking.  The display is on all the time.  The motor only runs at high power about half the time.  So it's really more like 1 amp.  Now the ratio is more like 4:1.  We don't have good data on the motor current, so no one has paid attention to the battery time.
> >
> > There are so many holes in this net.  lol
> >
> > BTW, does anyone understand what Phil Hobbs is going on about???  Why does he talk in code?
> >
> 
> If you are switching a 2 amp motor load, then you already have more
> problems than a point of use regulator, in terms of supply load step
> function. If it's a dc brush motor, perhaps permanent magnet, that
> looks like little more than 0 ohms, or nearly a short circuit at rest,
> so you will need to ramp that up to limit current. Once spun up,
> power is more or less proportional to load, but unless the data
> sheet has all the info, you will need to build a mechanical test rig
> to define the motor characteristics. I would do that anyway, to get
> a idea of what size motor is needed and optimise the circuit
> to drive it.
> 
> There's quite range of ic's for motor control, with soft start,
> current limiting etc. You could perhaps use a brushless moter and
> again, some ic choice on how that's done. Advantage is zero
> commutator noise to upset other things. You really can't just use a
> relay to switch that motor.

Done and dusted.  Not sure why you are going off on this tangent. 


>  > BTW, does anyone understand what Phil Hobbs is going on about???
>    Why does he talk in code?
> 
> Iirc, if he will excuse the comment, Phil is a scientist, Science is
> about math and numbers, measurement accuracy, whereas electronics,
> once you get the theory  under the belt, as more about experience,
> knowing what works, what doesn't and not a little intuition...

Ah, so that's why he says things like, "zilch" with no context?  Got it.  

He seems to like playing mind games... mostly with his own mind.  Talking around things without explanations is just screwing with yourself. 

-- 

  Rick C.

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#29932

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> BTW, does anyone understand what Phil Hobbs is going on about???  Why
> does he talk in code?

I think part of the idea might be that linear regulation is very simple
compared to switchers, so it has fewer ways to go wrong despite lower
efficiency.  Either way though, I'm used to regulated P/S having an
overvoltage crowbar that shuts things down if the regulation fails, and
in the case of a ventilator it is presumably never ok to shut down.  So:
backups for the backups.

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#29934

On Friday, August 7, 2020 at 9:10:30 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.deletethisbit@gmail.com> writes:
> > BTW, does anyone understand what Phil Hobbs is going on about???  Why
> > does he talk in code?
> 
> I think part of the idea might be that linear regulation is very simple
> compared to switchers, so it has fewer ways to go wrong despite lower
> efficiency.  Either way though, I'm used to regulated P/S having an
> overvoltage crowbar that shuts things down if the regulation fails, and
> in the case of a ventilator it is presumably never ok to shut down.  So:
> backups for the backups.

I don't recall anyone talking about failure other than higher temperatures resulting in higher failure rates.  

I don't know what he was going on about.  The layout of the board was ducked up.  The guy forgot to override the default thermal isolation of the thermal pad on the regulator.  The next board spin won't have that problem and the regulator won't shut down from excessive heat in the regulator.  

No one in the design group has said the device has to have any special reliability rating.  

I remember working on a military radio with secure encryption.  There was an odd circuit with many switches.  I could not find anyone who could explain how it worked, but it seemed to have to do with no single point of failure sort of thing.  When I say "many", I mean MANY, like fifty separate SPST SC-70 devices.  When a circuit has built in redundancy, how do you check to assure the redundancy is working?  I guess they would have to add a means of disabling the redundant part as well as the primary part separately.  But then how do you know your disabling circuit is working???  

At some point there has to be a single point of failure.  In nuclear power plants, if nowhere else, it is the procedures.  If they are wrong, they are wrong through and through with no back up.  The North Anna reactors went offline in the earthquake a few years ago.  One of the diesel generators failed.  When they researched the failure they found it was due to a faulty installation procedure that was common to all of the generators.  A single point of failure. 

-- 

  Rick C.

  -+-+ Get 1,000 miles of free Supercharging
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#29922

On 8/7/2020 14:30, Chris wrote:
> On 08/07/20 02:50, Phil Hobbs wrote:
>> On 2020-08-06 19:01, Chris wrote:
>>> On 07/08/20 23:20, Rick C wrote:
>>>
>>>> I'm also concerned about the board layout.  The board is not at all
>>>> dense but there are several
>>>
>>> parts that need copper area for heat sinking.  They are using a linear
>>> regulator to drop 12+ volts
>>>
>>> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!  So the 5V
>>> regulator gets quite warm,
>>>
>>> 70°C!!!
>>>
>>> You should be concerned. The whole thing about safety critical kit is
>>> that it should be conservatively designed, with all parts running well
>>> within their ratings. If the hw bod is happy with a regulator running
>>> at 70c, he must be clueless. Sorry, but it needs to be said.
>>>
>>> If you care about your professional career and any litigation
>>> issues, you should either have enough influence on the project
>>> direction to stop design errors like that, or just walk away from it...
>>>
>>> Chris
>>
>> Hmm, interesting. Most linear regulators I'm familiar with are rated to
>> 125 C junction temperature, and some higher. What safety or regulatory
>> issues have you run into that were caused by running some part 55C below
>> its rated temperature?
>>
>> Cheers
>>
>> Phil Hobbs
>>
> 
> That's not the point and reliability is affected by temperature. It may
> not matter for a short lived down hole item where failure has no safety
> implications, but not good enough otherwise. The constant temperature
> cycling will affect wire bonds and reliability. Cheap tacky design,
> using a linear regulator to go from 12v to 5, then 3.3, considerable
> current, where a point of use switcher would be a far more efficient and
> probably more reliable solution as well Wasted power needs a bigger 
> backup battery etc...
> 
> Chris
> 
> 

A 7805 at 70C is not too hot, nothing like that. I'd be worried of any
nearby electrolytic capacitors, I have seen these fail if put too close
to some hot part. Once on a product of mine - though the board was "too
hot" only for one cap of a particular series, other units have worked
for well over 5 years 24/7. And once I repaired our TV set (some 15+
years ago, a CRT one), it had an electrolytic cap next to a "red" hot
7805.
I have *never* seen a 78xx regulator fail because of overheating
and I have designed in quite a few. One can have them run hot
within reason, just keep in mind that they have temperature protection
and if you overheat one it will protect itself by more or less
cutting off the power at its output.
Another thing to keep in mind is to not forget to put a diode
in parallel if the output voltage is > say 5-6V; they do die
if the input goes 0V or so with the output capacitor charged.

Dimiter

======================================================
Dimiter Popoff, TGI             http://www.tgi-sci.com
======================================================
http://www.flickr.com/photos/didi_tgi/

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#29923

On Friday, August 7, 2020 at 1:42:37 PM UTC-4, Dimiter wrote:
> On 8/7/2020 14:30, Chris wrote:
> > On 08/07/20 02:50, Phil Hobbs wrote:
> >> On 2020-08-06 19:01, Chris wrote:
> >>> On 07/08/20 23:20, Rick C wrote:
> >>>
> >>>> I'm also concerned about the board layout.  The board is not at all
> >>>> dense but there are several
> >>>
> >>> parts that need copper area for heat sinking.  They are using a linear
> >>> regulator to drop 12+ volts
> >>>
> >>> to 5V and 3.3V.  The back lights for the LCDs draw 300 mA!  So the 5V
> >>> regulator gets quite warm,
> >>>
> >>> 70°C!!!
> >>>
> >>> You should be concerned. The whole thing about safety critical kit is
> >>> that it should be conservatively designed, with all parts running well
> >>> within their ratings. If the hw bod is happy with a regulator running
> >>> at 70c, he must be clueless. Sorry, but it needs to be said.
> >>>
> >>> If you care about your professional career and any litigation
> >>> issues, you should either have enough influence on the project
> >>> direction to stop design errors like that, or just walk away from it...
> >>>
> >>> Chris
> >>
> >> Hmm, interesting. Most linear regulators I'm familiar with are rated to
> >> 125 C junction temperature, and some higher. What safety or regulatory
> >> issues have you run into that were caused by running some part 55C below
> >> its rated temperature?
> >>
> >> Cheers
> >>
> >> Phil Hobbs
> >>
> > 
> > That's not the point and reliability is affected by temperature. It may
> > not matter for a short lived down hole item where failure has no safety
> > implications, but not good enough otherwise. The constant temperature
> > cycling will affect wire bonds and reliability. Cheap tacky design,
> > using a linear regulator to go from 12v to 5, then 3.3, considerable
> > current, where a point of use switcher would be a far more efficient and
> > probably more reliable solution as well Wasted power needs a bigger 
> > backup battery etc...
> > 
> > Chris
> > 
> > 
> 
> A 7805 at 70C is not too hot, nothing like that. I'd be worried of any
> nearby electrolytic capacitors, I have seen these fail if put too close
> to some hot part. Once on a product of mine - though the board was "too
> hot" only for one cap of a particular series, other units have worked
> for well over 5 years 24/7. And once I repaired our TV set (some 15+
> years ago, a CRT one), it had an electrolytic cap next to a "red" hot
> 7805.
> I have *never* seen a 78xx regulator fail because of overheating
> and I have designed in quite a few. One can have them run hot
> within reason, just keep in mind that they have temperature protection
> and if you overheat one it will protect itself by more or less
> cutting off the power at its output.
> Another thing to keep in mind is to not forget to put a diode
> in parallel if the output voltage is > say 5-6V; they do die
> if the input goes 0V or so with the output capacitor charged.

No, a 7805 isn't going to burn up when it is too hot because they shut off when overheating which is what this one was doing.  That is very inconvenient when working on a circuit.  I don't think the user would appreciate it either... especially when it is being used on a patient. 

I've actually become very demoralized about this project.  Not only is it being designed not unlike a hobby project (aside from my circuits, lol) it seems the project lead is getting tired of working on this and now that we are starting to generate a requirement document, massive corners are being cut.  Yesterday he literally justified not extending the requirements to the board design because it would take too much time.  

I've been thinking he was talking about schedule when he talked about time before.  But now I realize he is talking about HIS time and others on the project.  Their commitment is wearing a bit thin I guess.  

It's just that I've been pushing for defining clear, unambiguous requirements for a few weeks now and I thought we were going to have that.  Yesterday the project lead and the requirements lead are saying it doesn't need to be rigorous because whoever takes this over to manufacture will have to redo it all anyway.  

So the bottom line is with no requirements, that means we are already done! 

-- 

  Rick C.

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#29788

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> I had a friend who worked on medical devices for a while before
> getting out.  He said they required that you "prove" your design will
> not hurt the patient in any way.  Hard to do with a ventilator.

There are different levels of approval for medical devices in the US.
The lowest level would be for something like crutches, which can't
really hurt the patient unless you do something really dumb, so you
basically prove that you followed established practices instead of doing
something dumb.  More invasive devices like pacemakers or ventilators
need much more intense testing and approval.  One thing I remember being
told was that you have to document the design and development (including
the software) every step of the way.  There was a guy here on
c.a.e. some years ago who did that stuff and I learned some things from
him.  It is one of the reasons I got interested in Ada.

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#29792

On 2020-07-08 10:19, Rick C wrote:
> On Wednesday, July 8, 2020 at 8:14:05 AM UTC-4, Stef wrote:
>> On 2020-07-08 Rick C wrote in comp.arch.embedded:
>>> Wow!  Designing in a group is strange.  I'm helping with the
>>> design of a ventilator and it is a unique experience.  We have
>>> people of many skill levels and talents, many I don't even know.
>> 
>> That is the good part of designing with a group. You can have many
>> more talents and skills than can be combined in a single person.
>> For a medical product like this you need medical, software,
>> hardware, mechanical and lots more skills. Not something that can
>> be found in one person very often.
>> 
>> <snip, some project frustrations etc.>
>> 
>>> I literally have no idea how they are ever going to get this
>>> thing past any sort of approval process.  No one working on the
>>> project even seems to understand what is required.
>>> 
>> 
>> This is very worrying. As David already explained, documentation
>> and approval is a very large part of medical device development.
>> There is this famous Boeing quote about the weight of the paperwork
>> required for a plane. I think you can extend this to medical
>> devices as well.
>> 
>> Did they at least have a look at some standards that apply to
>> ventilators to check what will be required? I would start off with
>> IEC 60601-1, IEC 62304 and ISO 80601-2-12, make sure you use the
>> latest versions. But there will be more.
>> 
>> And this should have been done before the first schematic was drawn
>> or line of code was written. Some standards put requirements on the
>> development process and you can not comply with those if you start
>> your certification efforts after the development is completed.
>> 
>> 
>>> I guess I'm a bit frustrated by the lack of organization.  I'd
>>> like to step away, but the person acting as a leader seems to
>>> want me in the group.
>>> 
>>> There is some work of my own I should do, so maybe I'll stick
>>> around to get to rev 2 of the board and then step out.
>>> 
>> 
>> If there has indeed been done nothing on the certification side, my
>> feeling would be to step away as well.
>> 
>> 
>>> I guess I'm used to working on my own.
>>> 
>> 
>> Yes, than all is in your own hands. ;-)
>> 
>> But the advantage of a team is that you can concentrate on what you
>> are good at and let others do what they are good at. And if the
>> team is diverse and skilled enough (and properly led) the end
>> result will be better that that of a single developer.
>> 
>> And I think a lot of medical device stuff can not be done by a
>> single person. There are many cases where you need an (expert)
>> reviewer in the process. Reviewing your own work is less than
>> optimal. ;-)
> 
> It seems the UK has an abbreviated set of requirements for response
> to COVID-19 and that is what they are mostly working with.  I forget
> the name of it.
> 
> They do get advice from time to time from professionals in the field.
> My main concern is a direction they are currently going in where more
> and more valves, pressure relief, etc. is being added to the tubing
> right at the patient.  I'm not sure how it all will be held in place.
> That and how they plan to get this through the approval process.
> 
> I had a friend who worked on medical devices for a while before
> getting out.  He said they required that you "prove" your design will
> not hurt the patient in any way.  Hard to do with a ventilator.

IANAL, but the liability implications of that would be interfering with
my sleep.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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