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
