Adjusting Sensitivity of Photo Transistor?

[audioguru]

Hi Adam,
Your phototransistor is upside-down, so no wonder it didn't have any gain.
When it is right-side up like this, it probably has too much gain, so the 100k collector resistor's value should be reduced. :lol:

 

[Nigel Goodwin]

A couple of comments really!.

1) You've labelled the decode an HT12E - this is actually an ENCODER chip - presumably you've labelled it wrong?.

2) If you're using IR you should feed the decoder chip from an IR receiver IC, this cures all your problems over the IR reception. Plus it strips off the 38KHz modulation employed on the transmission. Using a simple photo-transistor will feed the 38KHz to the decoder, and prevent it from working.

I'm presuming you're using the correct IR encoder IC?, that gives the required 38KHz modulation?. If not, you're causing many more problems, and restricting your range and reliability.

 

[adamthole]

Yeah, I think I called it HT12D earlier when I meant HT12E. I am using the encoder chip HT12E, since it is for the transmitter. My transmitter is RF, not infrared. Everything works perfectly with my transmitter/receiver set up. The only problem I was having was with the red laser and the phototransistor.

Thanks for the info on the fact that my phototransistor was in backwards (looks at ground in shame). I still have trouble with which is the emitter/collector on the symbol.

I thought that if it were in wrong, it wouldn't work at all. The way I have it currently works. Obviously I am wrong. Please teach me

Thanks!

 

[ljcox]

I thought that if it were in wrong, it wouldn't work at all. The way I have it currently works. Obviously I am wrong. Please teach meThanks!

Transistors will work either way. But they have a much greater gain if connected in the correct manner.

Len

 

[audioguru]

Hi Adam,
A transistor has a small amount of gain when its emitter and collector are reversed, but the breakdown voltage is only about 5V to 8V. In your circuit, the 2N3906 PNP transistor was trying to do all the work.

The emitter of transistors are drawn with an arrow. It points away for an NPN and points towards the transistor for a PNP.
For an NPN transistor, its collector is always positive with respect to its emitter.
For a PNP transistor, its collector is always negative with respect to its emitter.

Your phototransistor will be much more sensitive by itself with it connected correctly. :lol:

 

[adamthole]

Alright, I'll try that out. Thanks for the info!

 

[chemelec]

2n5777

Where would I get one of those, I checked my 3 main suppliers (Mouser, Digi-Key, and Jameco) and none of them had it, or atleast I didn't find it. When I did a search on google for it I just got all of those sites that list as many part numbers as possible, and are basically useless. Thanks for the info though. When I bought the phototransistor I am using from jameco I thought it was best for visable light. I'll have to memorize the color wavelengths.

Thanks!

Really Old Post, But:

For your info or Anyone else here, I Now Stock the Origional GE, 3 lead "2N5777". I also have the data Sheet for it at:

**broken link removed**

 

[vheerdg]

Hi there currently im using a nte3032 photo transistor but im having difficulty with sensitivity can any one help plz.