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Re: control a relay from the pi via GPIO

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On Thu, 7 Jul 2016 10:44:58 -0000 (UTC), Gordon Henderson
<gordon+usenet@drogon.net> wrote:

>In article <nljpg6$me8$1@dont-email.me>,
>Björn Lundin  <b.f.lundin@gmail.com> wrote:
>>Hi!
>>I got a pi model B that I want to control a relay.
>>
>>I've got one just like the ome on the picture in the link here
>>
>><https://halckemy.s3.amazonaws.com/uploads/image_file/file/76359/PoolSchematicDC.jpg>
>>
>>
>>I connect just as the picture, +5v to vcc and ground to ground.
>>The green diod then ligths up.
>>
>>So I connect a gpio to the middle pin marked Inl.
>>GPIO low = nothing happens
>>GPIO high = nothing happens.
>>
>>I grab a voltmeter and measure between the GPIO and ground,
>>and I get ca 0 V resp 3.3 V. So - correct pin, but no action in the relay.
>>
>>Ok, thinking 3.3 might be to small to drive the relay, testing +5 V on
>>the middle pin. Still nothing.
>>Frustrated - testing ground to middle pin - and then the relay clicks,
>>and the red diod lights up, somewhat brighter than the green one.
>>
>>Surley - this is not supposed to happen - or ?
>>
>>I got 3 of those relays, and all three behave the same - ground the
>>middle pin and then action.
>>
>>
>>What am I doing wrong here?
>
>Several things.
>
>Firstly you've bought a cheap relay board which may have said "Raspberry
>Pi" on it website, but it really is not Pi compatible. This happens a lot,
>especially with sellers in far-off land you have no way to get in-touch
>with. They lie and use the Raspberry Pi name to lure unsuspecting buyers.
>
>So the relay board - the real issue is that it's designed for 5v
>operation. It's really for an Arduino or similar running at 5v. The Pi's
>3.3v combined with the resistor into the opto coupler does not provide
>enough "oomph" to light the internal LED and activate the relay. Thats
>the case with most of these cheap boards...
>
>... however - another issue is that sometimes these relay boards (and I've
>seen dozens of different ones )-: effectively connect the LED + resistor
>to the 5v line - expecting the driving computer to short it to 0v.
>
>Try this:
>
>Leave it wired as it is, but then remove the wire from the Pi'2 GPIO
>pin 22 and connect it to 0v/Gnd.
>
>If the relay fires then you have one of these.
>
>And by reading the above, this is most likely.
>
>So do this:
>
>  Re-connect it to the Pi on that pin (bcm_gpio 22)
>
>and run these commands:
>
>  gpio -g mode 22 in
>
>Realy ought to be off and stay off.
>
>  gpio -g write 22 0
>
>Nothing should happen at this point.
>
>  gpio -g mode 22 out
>
>Relay should click ON. The pin is in output mode and is sinking
>the current from the 5v, via the resistor + LED to 0v.
>
>  gpio -g mode 22 in
>
>Relay should click off.
>
>I've seen this make similar relay boards work. It works, BUT ... when
>in the off state (ie. gpio pin is in input mode), you are presenting 5v
>to the GPIO pin. fortunately via a resistor and diode and the input
>protection diodes on the GPIO pin will limit the damage, but it's very
>not recommended. It'll work, but for how long...
>
>Really, you need to throw this relay board away and get something designed
>for the Pi. Use something like a PiFace board.
>
>Gordon
>(Author of wiringPi)

The two-relay board I mentioned works perfectly with a pi, and is
1/20th the price of a piface.

Common emitter buffers, opto-isolators, and channel LEDs

The 8 channel version I am playing with now only cost £3.03

I am using it on my RASPBX with 16 shell scripts called from
extensions_custom.conf  with appropriate voice confirmation.

All great fun, but I can't think of any uses for it at the moment.










-- 

Graham.

%Profound_observation%

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Thread

control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-06 22:24 +0200
  Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-06 16:45 -0400
    Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-06 17:03 -0400
      Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-06 18:00 -0500
        Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-06 21:10 -0500
          Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-06 23:55 -0400
            Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-07 12:30 -0500
      Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-07 19:21 +0200
        Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-07 14:34 -0400
          Re: control a relay from the pi via GPIO Dennis <dennis@none.none> - 2016-07-07 17:10 -0500
            Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-08 00:29 -0400
        Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-12 10:18 +0200
          Re: control a relay from the pi via GPIO Rob Morley <nospam@ntlworld.com> - 2016-07-12 12:49 +0100
  Re: control a relay from the pi via GPIO Gordon Henderson <gordon+usenet@drogon.net> - 2016-07-07 10:44 +0000
    Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-10 17:40 +0200
      Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-10 12:43 -0400
        Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-12 10:06 +0200
          Re: control a relay from the pi via GPIO The Natural Philosopher <tnp@invalid.invalid> - 2016-07-12 09:20 +0100
          Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-07-12 04:23 -0400
            Re: control a relay from the pi via GPIO The Natural Philosopher <tnp@invalid.invalid> - 2016-07-12 09:58 +0100
    Re: control a relay from the pi via GPIO Graham. <graham-usenet@mail.com> - 2016-07-11 23:10 +0100
  Re: control a relay from the pi via GPIO Graham. <graham-usenet@mail.com> - 2016-07-08 21:45 +0100
    Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-10 17:26 +0200
      Re: control a relay from the pi via GPIO Graham. <graham-usenet@mail.com> - 2016-07-11 22:13 +0100
        Re: control a relay from the pi via GPIO Björn Lundin <b.f.lundin@gmail.com> - 2016-07-12 10:00 +0200
  Re: control a relay from the pi via GPIO Big Bad Bob <BigBadBob-at-mrp3-dot-com@testing.local> - 2016-08-18 10:08 -0700
    Re: control a relay from the pi via GPIO rickman <gnuarm@gmail.com> - 2016-08-18 16:40 -0400

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