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Infrared Remote Control - corrections?

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Menticol

Active Member
Hello!

I've found this simple circuit on the net, It's an single channel IR remote control. I hope somebody could find it useful.

The only problem is, I got it from a site with bad reputation of non working schematics - It's pablin.com.ar, to avoid copyright issues.

Should I correct something, before starting etching?

Emmiter
5480-tx.gif


Receiver
5481-rx.gif


(Receiver needs +9v -9v to work)

Thank you in advance
 

audioguru

Well-Known Member
Most Helpful Member
It is the same defective very old circuit at Aaron's Homepage .
The LM308 opamp has not been made for about 13 years.
It is missing a 100k to 1M resistor from its pin 3 to 0V for its 0V reference voltage.
The author didn't know that the -9V battery can be replaced by a couple of resistors.
 

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Menticol

Active Member
Damn! I just got the Lm308 today, 13 years old? Now I know why I had to pay a lot for it!!! :mad:

Please Audioguru, is the 100 ohm resistor (I have chosen it randomly between 100K and 1M) between pin 3 and GND, enough to avoid the using of -9V on pin 4? or where should the pin 4 be connected?

The datasheet doesn't give me any help.

Thank you in advance, and sorry by the nuisance
 
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audioguru

Well-Known Member
Most Helpful Member
The added 100k to 1M resistor (not 100 ohms) makes pin 3 input of the opamp at 0VDC when the opamp has a positive and negative supply. If the opamp has only a single positive supply then pin 3 must be biased at half the supply voltage with two resistors.
 

Menticol

Active Member
Thank you so much Audioguru, you saved my day again!

Is this the correct way to biasing pin 3?


5482-MDMA.jpg


I made the calculation as follows

Power consumption of the circuit: 300 mA
Supply voltage: 9V
R = 4,5 / 0,300 = 15 ohm

One last question: If my procedure is correct, can I feed the circuit with only 5V? My project will run with 12V, the LM308 can handle up to 18, but LM567 just can handle 9... and I have a 7805 at hand

Recalculating R1 again offcourse
 
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audioguru

Well-Known Member
Most Helpful Member
No.
Pin 3 is the input of the LM308. Its current is almost nothing, certainly not 300mA. The entire circuit draws about 10mA plus the current for the relay. The pin 3 input current of the opamp is only 0.0000000015A (1.5nA).

Your 15 ohm resistor is shorting the output signal from the photo-transistor and is shorting the input of the opamp to the positive supply where it does not work.

Pin 4 must be connected to 0V then pin 3 has a 1M (one million ohms) to ground and another 1M to the positive supply. Then pin 3 will be at half the supply voltage.
 

Menticol

Active Member
It doesn't work. When I adjust the Potenciometer, the relay activates only when I reach the end of it, and ignores the emmiter. At some point of the potenciometer scale one of the IC's starts making a high frecuency noise

tested with 2 pin and 3 pin IR receiver

Don't know what to do...
 
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audioguru

Well-Known Member
Most Helpful Member
The circuit is supposed to use a photo-transistor. It will not work with a photo-diode and it won't work with an IR receiver.
If the pins on the photo-transistor are backwards then the circuit will not work.
If the photo-transistor is in light then it probably will not work.
 
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