View Full Version : Help Using Phototransistor for line following

07-01-2008, 01:09 AM
This is my first time with phototransistors. Ive read some tutorials over the web and many posts here, and also seen many circuit diagrams using phototransistors. But I cnt figure out what I am doing wong. I cant refer the datasheets however as I dont know what this phototransistor that i have, is called. Its just like an LED but dark, blackish and opaque. I searched for datasheets for phototransistors, but there are so many different datasheets for different phototransistors, that it confuses me more.

Refer to this circuit:


Im expecting that if I connect the V out from phototransistor to the Multimeter, then I should be able to see remarkable variation in the voltage. I dont want to connect it to the ADC of MCU without confirming that it is giving proper voltage variation.

07-01-2008, 10:06 AM
You have an IR detector LED, not a PhotoDiode............

[Please keep to the point and describe the component/problem etc., in detail instead of other things. This will make it clear to the readers. There is no need to tell US about your search etc.,....!
- Mod ]

07-02-2008, 02:23 AM
It looks like a led, but it is a phototransistor for example a SFH300 (http://www.reichelt.de/?;ACTION=3;LA=4;GROUP=A54;GROUPID=3045;ARTICLE=605 52;START=16;SORT=order_col_artnr_besch;OFFSET=16;S ID=25v434s6wQARkAAEVNy0I8d9a6ae32245386ad57d863e84 04029a) but you don't know which typ you have. You can test it. All you have to know is, which wire is the collector and which is the emitter. Connect 5V to a 10kOhm resistor and the other side from the resistor to the anode. connect the emitter to the ground. now you can measure with your multimeter between collector and ground. without light there is a high voltage ans with light on the phtotransistor, there is a smaller voltage. if there is no different voltage rotate the phototransistor. Tomorrow i make you a photo from my unknown phototransistor.