Infrared circuit not working

Thread Starter

regal006

Joined Jul 14, 2012
20
i can't make this circuit work. :(
how do you make an infrared circuit that will have a range of 2 - 3 meters.
i've been doing this circuit for days..
please help..

thanks a lot!
 

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R!f@@

Joined Apr 2, 2009
9,647
It will work.

Using pure DC is less efficient. The 555 will pulse the led. This will increase the distance and efficiency.

I know u did not try what I suggested. but try putting more IR leds in parallel but for this a transistor is necessary.
 

absf

Joined Dec 29, 2010
1,942
I think you connected the infra LED D1 polarity wrongly. When the output of 555 is high, the led wont conduct due to both Anode and Cathode are at same potential. When output is low, D1 would not conduct as the polarity of LED is wrong.

The negative supply of the 741 was not connected too. Where is the -9V for the 741?

Allen
 

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Thread Starter

regal006

Joined Jul 14, 2012
20
@R!f I did but it still doesn't work.

@absf i tried different turning the ir led and the phototransistor . i even used photodiode. still nothing happens

sorry forgot to put ground on op amp
 

MrChips

Joined Oct 2, 2009
19,280
What is C2, 1μF across IC2 in the original circuit for?
Also I think you have the +ve and -ve inputs reversed.
I guess I don't know what that circuit is trying to do.
 

Thread Starter

regal006

Joined Jul 14, 2012
20
i don't know either what the op-amp does with this. :(
anyway . i'll do what they said. i'll come back later this evening if i still doesn't make this circuit work. need to go to school.

thanks a lot for those who replied
 

absf

Joined Dec 29, 2010
1,942
I changed your circuit a bit and it worked.

The U2 op-amp is used as a comparator. When the photo transistor detects a signal it conducts and thus lower the voltage of the negative input of the opamp. The reference at + input is set to 1/2 Vcc. When no signal is detected, the output is low so the LED is off.

My simulator doesn't have the IR led and photo transistor so I used an opto coupler instead. I put a button on the transmitter so you can test the Rx and also saves the battery life.

Allen
 

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JoeJester

Joined Apr 26, 2005
4,077
You do realize the infrared led in your notes is also backwards, however, if it is working, you wired it in properly.

And the "receiver" in your notes is not a comparator.
 

JoeJester

Joined Apr 26, 2005
4,077
741 is an op amp

You can use it in a comparator circuit, but that is not what you have drawn. You have a reference of zero volts but zero chance of crossing that threshold to change the output state. absf has shown the 741 in a comparator circuit in his drawing above.

Can you explain the receiver circuit you have drawn on your notes?
 
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