For a school project, I need to create a circuit which registers whenever a red laser hits a photoresistor, and displays the number of counts in a LED bar graph.
It seems that CMOS 4017 is the right choice for counting and driving the LEDs - that part is easy and obvious. The difficulty I'm anticipating is in producing a reliable input pulse for the 4017, since the amount of time the laser hits the LED may vary significantly from a quick pass over the sensor to hovering over the sensor for 1 second or more.
I suspect the answer is to use a 555 monostable circuit on the input. I found the following link via the wonder that is Google:
I'm thinking the 3rd to last circuit is basically what I want - trigger on the leading edge of the voltage spike coming from the photoresistor (wired as a voltage divider as input to this).
Is this going to do it for me?