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Topic: Reading a IR transistor, need to amplify? (Read 126 times) previous topic - next topic

daveyjones

I have an IR transistor that seems to work for my needs.  I used a multi-meter on 20K range (ohms) and the transistor drops in value when light is present. 

So my goal is to turn on an read the transistor value, then turn IR emitter on & read again --if the value is lower, I know there's an IR source.

At 20K ohm range, the transistor reads 12,3 , with an IR light source drops to 12.1  Lower ranges yield no readings.

Is there a simple amplifier circuit I could use to make it appear as a greater difference?  I realize than any amplifier circuit will also amplify noise...
I am not an EE, I am learning as I go...

LarryD

The way you have it in your schematic isn't the same as how you have it wired up!

daveyjones

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?search_type=jamecoall&catalogId=10001&freeText=112176&langId=-1&productId=112176&storeId=10001&ddkey=http:StoreCatalogDrillDownView

LarryD

Your device is meant to be used in an on (saturated) and off (cutoff) condition.
I suggest you look at an IR plastic filter to make this into the IR detection circuit that you want.
The way you have it in your schematic isn't the same as how you have it wired up!

LarryD

#4
Jun 30, 2015, 08:01 pm Last Edit: Jun 30, 2015, 08:02 pm by LarryD


You can take your reading at the emitter.

.
The way you have it in your schematic isn't the same as how you have it wired up!

daveyjones

Hmm. Ok thanks.  I thought it was something it isn't...
I did a quick search for IR filters, and too expensive to be a viable option...
thanks.

Wawa

I did a quick search for IR filters, and too expensive to be a viable option...
Use the black plastic front (if it has one) from an old remote control.
Leo..

Magician

http://coolarduino.blogspot.ca

daveyjones

Nice idea (remote) -- I will pick up a couple @ goodwill / thrift stores - I'm sure they will have them cheap.
--
Thanks for the link; will give it a try too.

I never thought just detecting IR light presence would be so difficult.. of course, I don't really know what I'm doing, so it's all a bit trial and error.

Thank you for your help

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