Newsgroups: sci.electronics
From: schuch@phx.mcd.mot.com (John Schuch)
Subject: IR Opto Detector Schematic Diagram
Date: Thu, 15 Jul 1993 19:37:04 GMT


I received a lot of requests for this so I'll go ahead
and post it. This is a "cheap'n'dirty" circuit designed
for minimum part's count, not sound quality or gain.

Have fun.

John

______________________________________________________________


Infrared Light Detector : (c) 1993 John R. Schuch
____________________________________________________

This circuit converts infrared light into sound.
Modulated IR light, like that from remote controls,
IR received by the phototransistor and is amplified by
the LM386 IC. The IC in turn drives a small 8 Ohm
speaker. Unmodulated IR light, like that from an
incadescent light bulb, produce no sound so the
phototransistor also turns on an LED indicating the
presence of IR light.
____________________________________________________

                      _________________
                      [IR Photo Trans.]
9Vdc----[20K RES]--+--[emit       coll]--+--[20K RES]----Gnd
                   |  [____ base______]  |
                   |                     +---------------------+
                   +--[10K Ohm Pot]--Gnd                       |
                             ^                                 |
    +------------------------+                                 |
    |         LM386                                            |
    |       +---u---+                                          |
    |     nc|1     8|nc                                        |
    +-------|2     7|nc                                        |
         Gnd|3     6|9Vdc                                      |
         Gnd|4     5|-----[+100uF-]--[8 Ohm Skeaker]--Gnd      |
            +-------+                                          |
                      +----------------------------------------+
                      |
             [       base       ]
      +------[emit          coll]-----[270 Ohm]---9Vdc
      |      [Gen Pur NPN trans.]
      |
      +------[LED  |>| ]----Gnd

____________________________________________________________

NOTES:

- All of the parts for this circuit are available from your
  local Radio Shack for a few dollars. RS also has a great
  little case for the project (# 270-294), but you better
  build it small.

- My prototype used the phototransistor from the index sensor
  of a junked floppy disk drive. Make sure you get the
  transistor and not the IR LED, they look very simular.

- The transistor driving the LED can be any general purpose
  NPN device. 2N2222 and 2N3904 are a couple of common parts
  that will work.

- The LM386 amplifies the incomming signal by about 20 times.
  The potentiometer adjusts the level of the signal feeding
  the amplifier. Adjust the pot until amplifier starts to feed
  back and then back it off a little. See the data sheet for
  the LM386 for details about increasing the gain.

- This circuit was designed as a quick, simple tester to check
  IR remote controls and as such was designed to use as few
  parts and cost as little as possible. The design could be
  improved for audio fidelity, sensitivity and gain. I'd love
  to see any improvements you make.


John

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