Groups > alt.folklore.computers > #155229

Re: 1957 LED

From	Michael Black <et472@ncf.ca>
Newsgroups	alt.folklore.computers
Subject	Re: 1957 LED
Date	2015-12-15 15:05 -0500
Organization	National Capital Freenet, Ottawa, Ontario, Canada
Message-ID	<alpine.LNX.2.02.1512151503510.5698@darkstar.example.org> (permalink)
References	(1 earlier) <n4cib8$se5$1@dont-email.me> <396e97cc-39db-46fe-8404-b8c60ec255df@googlegroups.com> <e2d26d9c-7353-4cbb-9c1b-ef85199a2621@googlegroups.com> <sLOdnVJVds5_1_LLnZ2dnUU7-VWdnZ2d@giganews.com> <XnsA5717968B3B92falkarcabca@213.239.209.88>

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On Tue, 15 Dec 2015, Alfred Falk wrote:

> Jon Elson <jmelson@wustl.edu> wrote in
> news:sLOdnVJVds5_1_LLnZ2dnUU7-VWdnZ2d@giganews.com:
>
>> Quadibloc wrote:
>>
>>> On Friday, December 11, 2015 at 8:31:35 AM UTC-7, hanc...@bbs.cpcn.com
>>> wrote:
>>>
>>>> When I was young, the automatic doors in supermarkets were almost
>>>> all controlled by a pressure-sensitive flood mat.  It was very
>>>> rare to see a door controlled by photo cells.   I think today they
>>>> use a motion sensor, not the floor mat.
>>>
>>> I think the popular method is something called "passive infrared".
>>> Which sounds like a heat sensor.
>
>> No, there really were visible beam systems in use in the 1950's.  They
>> had heavy stainless bars and poles next to the doors, and if you got
>> down low you could see they had slots in the vertical poles.  One side
>> of the "gate" had an incandescent lamp and a lens in it, the other side
>> had a vacuum photodiode.
>>
>> Jon
>
> I remember those very well.  My brother and I (we were maybe 10 and 11)
> spent a fair bit of time, while waiting for our parents to finish their
> interminable shopping, trying to figure out how they worked.  Simply putting
> a hand in the beam did not open the door, but walking through did.  We
> conjectured a weight sensor in the floor, but couldn't verify that either.
> There was obviously something we were missing.  Too many experiments would
> bring us to attention of staff who would shoo us away.
>
>
I remember wanting to make something like that, but so early that I didn't 
have all the knowledge I needed.

Since the photocell dropped resistance with light, I initally couldn't 
figure out how that would work.  When the light wasn't interrupted, the 
photo cell would let the voltage from the battery to the bell (I was 
thinking in terms of "burglar alarm"), but it was when the light was 
interrupted that you needed the bell.

It was later that I learned about relays and transistors that could invert 
things properly.

   Michael

Thread

1957 LED hancock4@bbs.cpcn.com - 2015-12-10 11:03 -0800
  Re: 1957 LED Al Kossow <aek@bitsavers.org> - 2015-12-10 11:06 -0800
    Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-10 14:44 -0500
      Re: 1957 LED hancock4@bbs.cpcn.com - 2015-12-11 07:41 -0800
        Re: 1957 LED Ahem A Rivet's Shot <steveo@eircom.net> - 2015-12-11 16:37 +0000
        Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-11 14:42 -0500
    Re: 1957 LED philo <philo@privacy.net> - 2015-12-10 13:56 -0600
      Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-10 22:59 -0500
        Re: 1957 LED "Osmium" <r124c4u102@comcast.net> - 2015-12-11 08:20 -0600
          Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-11 14:33 -0500
      Re: 1957 LED Quadibloc <jsavard@ecn.ab.ca> - 2015-12-13 07:58 -0800
        Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-13 13:00 -0500
      Re: 1957 LED Lon <lon.stowell@comcast.net> - 2015-12-13 12:48 -0700
        Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-14 09:07 +0000
          Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-14 11:47 -0500
          Re: 1957 LED rpw3@rpw3.org (Rob Warnock) - 2015-12-16 14:55 +0000
            Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-16 16:32 +0000
              Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-16 14:17 -0500
              Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-16 18:15 -0600
                Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-17 07:58 +0000
                Re: 1957 LED Andrew Swallow <am.swallow@btinternet.com> - 2015-12-17 13:21 +0000
        Re: 1957 LED Ingo Paschke <ipaschke@lpclabs.de> - 2015-12-14 11:11 +0100
    Re: 1957 LED Stephen Wolstenholme <steve@easynn.com> - 2015-12-11 10:58 +0000
      Re: 1957 LED Lon <lon.stowell@comcast.net> - 2015-12-13 12:50 -0700
        Re: 1957 LED Stephen Wolstenholme <steve@easynn.com> - 2015-12-14 12:57 +0000
          Re: 1957 LED "gareth" <no.spam@thank.you.invalid> - 2015-12-14 14:07 +0000
            Re: 1957 LED Stephen Wolstenholme <steve@easynn.com> - 2015-12-14 14:33 +0000
    Re: 1957 LED hancock4@bbs.cpcn.com - 2015-12-11 07:31 -0800
      Re: 1957 LED Quadibloc <jsavard@ecn.ab.ca> - 2015-12-13 07:42 -0800
        Re: 1957 LED Ahem A Rivet's Shot <steveo@eircom.net> - 2015-12-14 09:39 +0000
        Re: 1957 LED Jon Elson <jmelson@wustl.edu> - 2015-12-14 17:07 -0600
          Re: 1957 LED Alfred Falk <falk@arc.ab.ca> - 2015-12-15 18:53 +0000
            Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-15 15:05 -0500
              Re: 1957 LED hancock4@bbs.cpcn.com - 2015-12-16 07:32 -0800
                Re: 1957 LED Alfred Falk <falk@arc.ab.ca> - 2015-12-16 17:23 +0000
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-16 14:23 -0500
                Re: 1957 LED Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2015-12-16 20:13 +0000
                Re: 1957 LED hancock4@bbs.cpcn.com - 2015-12-16 13:15 -0800
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-17 14:53 -0500
                Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-17 14:17 -0600
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-18 19:43 -0500
                Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-20 20:02 -0600
                Re: 1957 LED hancock4@bbs.cpcn.com - 2015-12-21 10:31 -0800
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-21 14:53 -0500
                Re: 1957 LED mausg@mail.com - 2015-12-21 20:27 +0000
                Re: 1957 LED Uncle Steve <stevet810@gmail.com> - 2015-12-17 18:48 -0500
          Re: 1957 LED davidmylastname@acm.org (David Griffith) - 2015-12-16 02:43 +0000
          Re: 1957 LED Mike Spencer <mds@bogus.nodomain.nowhere> - 2015-12-16 17:44 -0400
  Re: 1957 LED scott@slp53.sl.home (Scott Lurndal) - 2015-12-10 19:13 +0000
    Re: 1957 LED "gareth" <no.spam@thank.you.invalid> - 2015-12-10 20:17 +0000
      Re: 1957 LED Lawrence Statton <lawrence@sengiuo.mx> - 2015-12-10 17:10 -0600
      Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-10 23:00 -0500
        Re: 1957 LED isw <isw@witzend.com> - 2015-12-10 21:21 -0800
          Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-11 08:01 +0000
            Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-11 14:30 -0500
            Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-11 15:36 -0600
              Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-12 07:55 +0000
                Re: 1957 LED mausg@mail.com - 2015-12-12 11:20 +0000
                Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-12 15:39 +0000
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-12 10:50 -0500
                Re: 1957 LED Stan Barr <plan.b@bluesomatic.org> - 2015-12-13 08:00 +0000
                Re: 1957 LED "gareth" <no.spam@thank.you.invalid> - 2015-12-13 11:10 +0000
              Re: 1957 LED Lon <lon.stowell@comcast.net> - 2015-12-13 12:51 -0700
        Re: 1957 LED "gareth" <no.spam@thank.you.invalid> - 2015-12-11 10:59 +0000
          Re: 1957 LED Ahem A Rivet's Shot <steveo@eircom.net> - 2015-12-11 15:46 +0000
            Re: 1957 LED "gareth" <no.spam@thank.you.invalid> - 2015-12-11 17:37 +0000
              Re: 1957 LED Ahem A Rivet's Shot <steveo@eircom.net> - 2015-12-11 18:34 +0000
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-11 14:49 -0500
                Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-11 15:39 -0600
                Re: 1957 LED Bob Eager <news0005@eager.cx> - 2015-12-11 22:46 +0000
                Re: 1957 LED Michael Black <et472@ncf.ca> - 2015-12-11 19:07 -0500
                Re: 1957 LED Bob Eager <news0005@eager.cx> - 2015-12-12 01:04 +0000
                Re: 1957 LED Ahem A Rivet's Shot <steveo@eircom.net> - 2015-12-12 08:54 +0000
        Re: 1957 LED hancock4@bbs.cpcn.com - 2015-12-11 11:52 -0800
          Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-11 15:46 -0600
            Re: 1957 LED Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2015-12-11 22:56 +0000
        Re: 1957 LED "Charles Richmond" <numerist@aquaporin4.com> - 2015-12-11 15:35 -0600
        Re: 1957 LED Quadibloc <jsavard@ecn.ab.ca> - 2015-12-13 07:51 -0800
  Re: 1957 LED Lawrence Statton <lawrence@senguio.mx> - 2015-12-10 17:09 -0600

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