Hello,

I am new to circuits and I have just recently designed a "dark sensing" circuit using an op-amp, a photodiode and an led at the output. Is there a way to have two less at the output of the op amp where one turns on when the photodiode is covered and another one blinks when the photodiode is covered. I can not seem to get this to work. Thanks!

 

To get it to blink you will need an oscillator made from another op amp, 555 chip, or transistors ...or use a flashing led.

 

This is one way to get a single output to illuminate 2 LEDs.

 

To get it to blink you will need an oscillator made from another op amp, 555 chip, or transistors ...or use a flashing led.

I understand this. However I need one led to blink and on every led to light up. The voltage at the output changes when the photodiode is covered. Would I feed the output of the regular led into the input of another op amp and make the oscillating circuit?

 

Here's a video of one, I made a few years back:

Of course, no semiconductors used:

But, I suspect you want one that uses low voltages, and components that are not in the antique category. Your choice of photodetector may not be the best for a simple project. Photodiodes are fast, but their output current is very low, and needs amplification. For your needs a phototransistor may be a better option. In fact a common LED can be used as a photovoltaic detector. Yes, LEDs will output a small voltage, when hit with light ! Put your voltmeter leads across a simple red LED and shine a bright light at it. It will output several hundred millivolts, into the 1M+ load of your typical DVM.

Here's a quickly drawn circuit: