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Infrared detector circuit

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George L.

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hello,

I am trying to make a simple infrared emitter and reciver.

I am using an infrared LED, and an infared receiver (phototransistor) from radioshack.

The goal is for the receiver to turn on a transistor when the circuit senses infrared light from the LED. (Similar to a TV remote control).

The Problem is that the reciver only picks up the "light from the LED" at VERY close distances (10 inches).

I attached a circuit that I thought would make the receiver more sensitive, but instead it seems that the circuit is always ON, even when the phototransistor is in darkness.

More information is on the attachment below :D

Please help

Thanks,

George
 

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Try using an OP AMP comparator to control the output response setting of ur circuit. Give the output of the receiver circuit to the inverting input of the opamp & connect a potentiometer on the non-inverting input as the controlling element. ground the negative supply & give about 5 volts on the + supply terminal.
 
George L. said:
hello,

I am trying to make a simple infrared emitter and reciver.

I am using an infrared LED, and an infared receiver (phototransistor) from radioshack.

The goal is for the receiver to turn on a transistor when the circuit senses infrared light from the LED. (Similar to a TV remote control).

The Problem is that the reciver only picks up the "light from the LED" at VERY close distances (10 inches).

I attached a circuit that I thought would make the receiver more sensitive, but instead it seems that the circuit is always ON, even when the phototransistor is in darkness.

Because it's too sensitive, also the phototransistor is sensitive to visible light, not just IR.

You should use an IR receiver IC, and a 38KHz modulated transmitter (like a TV remote).
 
Nigel Goodwin said:
Because it's too sensitive, also the phototransistor is sensitive to visible light, not just IR.
You should use an IR receiver IC, and a 38KHz modulated transmitter (like a TV remote).

You may also find an IR filter useful (grab one off an old TV or VCR)
 
Your circuit doesn't have a load resistor, except for the extremely high input resistance of the voltmeter, so no wonder the circuit measures "on" all the time.
You didn't say which photo-transistor you used so I couldn't lookup its leakage current when off, which is amplified by both transistors maybe 40,000 times by their darlington connection. If the leakage current is extremely low at only 1 femtoamp, the output transistor will have a 40uA collector current and a high input resistance voltmeter will show it to be conducting very hard.
Use maybe a 10k resistor for a load for the darlington and just about any voltmeter will show the darlington to be off when the photo-transistor is dark. :lol:
 
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