IR Opto Detector

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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. 
  

Sources

  • John R. Schuch schuch[at]phx.mcd.mot.com

Category:InfraRed

 

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