Detecting presence of IR -

See this web page: http://www.circuitstoday.com/photo-relay-circuit

I cannot get it to work. I want to activate the NO contacts on a relay when ever IR light in the 800-950nm wavelength range strikes the IR Photodiode. The Photodiode does appear to work as it produces 0.6 volts at the leads whenever I shine a IR LED at it. But the above circuit activates the NO contacts all the time when the 9V source is applied, IR or no IR pointed at it.

I also tried it with 2 transistors (Darlington hookup) and that did nothing new.

Any help appreciated.

Mike Taylor
Katy TX

 

What did you use for D1? Can you show a photo of your arrangement? Are you sure you don't have the diode backwards?

You probably need a higher resistance than the 10k pot gives. Use a meter to look at the voltage on the base of the transistor.

 

You have R1 and D1 reversed.

 

What did you use for D1? Can you show a photo of your arrangement? Are you sure you don't have the diode backwards?

You probably need a higher resistance than the 10k pot gives. Use a meter to look at the voltage on the base of the transistor.

I used a clear plastic IR Photodiode purchased at Radio Shack in the correct wavelength range. What range voltage at the base is desired? I would guess low voltage when the IR LED is off and high when it is on?

Mike

 

You have R1 and D1 reversed.

That is what I was thinking. I have seen other circuit diagrams where that was the case.

Wow! I can't believe I got two responses here within minutes of my original post! Glad I found this forum!

What I want to do is turn on a wireless transmitter whenever an IR game camera comes on. I have the xmtr/rcvr's working fine. I hope this circuit will let me turn on an IR floodlight located some distance from the cameras.

I could spend $80 and get a IR Extender (wired) but what is the fun in that! Besides, I want wireless so I can locate an IR floodlight some distance away from the cameras.

A little about me - I'm retired and like to tinker!

Mike

 

Wow! I can't believe I got two responses here within minutes of my original post! Glad I found this forum!

Six minutes to, "win" ain't bad.

 

You have R1 and D1 reversed.

Thanks to your statement that R1 & D1 were reversed, I got it working! Now with the IR LED light off I get 0.0 volts across the relay coil. With the LED light on I get 8.5V across the relay coil. (12V relay) 8.5V is enough to activate the relay.

The IR LED light has to be within 3" of the photodiode. But, I'm only driving the 5V LED with 1.2V. I will try the circuit with one of my game cameras and should be able to get several feet away.

Thanks for the help!

Mike Taylor
Katy, TX

 

Howdy neighbor,

You can use a cell phone camera to see the infrared. You probably already knew that, but it is worth mentioning.

 

Howdy neighbor,

You can use a cell phone camera to see the infrared. You probably already knew that, but it is worth mentioning.

I made a small stick-on tab that will hold the Photodiode in front of the IR LED's on my game camera. The Pd is connected to a circuit that activates a micro relay that turns on a transmitter. The wireless receiver then turns on the remote IR floodlight. It does this before the game camera takes the first picture.

Thanks everyone for the help!

Mike