[vishnums]

I have the abouve circuit. It doesn't work. I keep on getting HIGH in the signal...How can I check it. Is there any problem with biasing.please help.

 

[Harald Kapp]

Welcome to electronicspoint.

The photodiode may not generate enough current to drive the transistor. What type of photodiode are you using (attach datasheet, please)?
Try to increase the value of R5 to e.g. 100kΩ - what happens?