I have a CCD camera that is triggered by an external TTL square wave. That is each time the camera sees a rising edge on the square wave it takes a picture. The square wave is being output from a custom microcontroller card when in capture mode. So far I have used a oscilloscope to verify that the microcontroller card is indeed in capture mode and outputing a square wave.
I want to create a small circuit where a LED is being controlled by the square wave signal (0->5V). That way I can instantly see if the camera is running or not.
I do not want to draw much current from the signal. I have some 2N700 mosfets. So I want to use one of these to amplify the signal.
This is what I have come up with so far:
Should this work? Is there some easy way (eg. change resistances, I have a wide range of resistances) to improve the design?
BTW the input impedance of my oscilloscope is 200k Ohms. Maybe the input impedance of my circuit should be in this ballpark?
I have tested the circuit with a function generator as input and it appears to work just fine. However when I use it on the real signal it blinks as expected for a while and then get stuck in high state for a while and then blinks again. The stuck in high state is not something I expected. Not sure if this is a problem with my circuit or the software running on the custom microcontroller card.
May it suffice to drive the led directly from the signal:
This should draw 5.5 mA from the output of the microcontroller. Would that be a problem?