I'm a bit of a noob, but am trying to manually build an IR receiver circuit from a photo diode and a few other parts (the circuit im trying to reproduce is shown @ http://online.physics.uiuc.edu/courses/phys405/P405_Projects/Fall2005/Nabil_IR_Remote_Control_Demodulation.pdf on page 2).
I haven't received all the parts yet, but I figured as I have the op amp and the photo diode I would try just putting the inverting amplifier stage (ie up to point A) together to see if I could see any output from a tv remote on my crappy usb oscilloscope. At some point I noticed a weird 12kHz almost square wave coming from the circuit, even with the photo diode disconnected (circuit diagram shown below).
I was wondering if anyone would be able to shed any light on what's going on? As you can see from the diagram is a very simple circuit, consisting of only a few resistors and an LF356N Op Amp.
Thanks for reading :)
EDIT: It's worth mentioning that I get the same effect with a load resistor across Vo (was using 10M Ohms).