Hello guys,

I am working on an application to detect red Light using a Fototransistor. The red LED which I have has a typicall light intesity of 4 mcd. I tried some Fototransistors, but I didn't get any result. I think it is because of the low intensity of the LED. Does anyone have a suggestion for a phototransistor or another component which can detect a 4 mcd LED?

 

From what distance?

 

I want to locate the fototransistor just in front of the LED so that a maximum of 5 mm distance will be between the fototransistor and the LED.

 

Do you only want to detect "red" or does that just happen to be the color of the LED you are trying to detect?

My sense is you will probably need additional gain stages, assuming you have the PT wired correctly in the first place.

Post a schematic.

 

Where is your circuit and picture ? ( otherwise it is like asking - my car won't start ? why won't my car start ? )

 

Use a Reflective-Proximity-Sensor.
Really easy and simple.
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There are 4 methods to enhance detection.
- hooding such as using heatshrink over a dome (photodiode) PD to block stray light or recess it behind an aperture
- Red colour lens filtering to block stray light
- High resistor shunt >> 1Meg or use an Op Amp to boost the signal.
- pulse the LED then amplify the frequency with a Q=10 BPF to improve SNR.

3 mcd, wow really old compared to the 21st century 20,000 mcd parts with 20 mA.

oops sorry 4 mcd.

 

I am working on an application to detect red Light using a Fototransistor

Never heard of a Fototransistor, but there are many varieties of phototransistors.
Which one do you have?

 

Without a schematic diagram of your circuit, we have absolutely no idea what you are doing, what components you are using, etc. Please post your schematic. Nothing fancy, it can be a phone shot of a paper towel as long as it shows all components and connections.

ak