Fall quarter I took a class about microcontrollers, and one of the things I built for that class was a stroboscope.  A stroboscope is a device which pulses a bright light at a user-input frequency.  This flashing light can be used to observe the motion of rotating or vibrating objects.  A fan for instance will appear to rotate very slowly or not at all.  A guitar string can be observed to move very slowly side to side, stand still stretched to one side, or even reverse direction.  This can also be used to find the frequency of some rotating/vibrating object.

This stroboscope has a variable frequency from 8Hz to 10kHz, in steps of 0.01Hz.  It has an LCD screen for easy reading and a set of four buttons to control the frequency.  Two one-watt LEDs provide the light pulse.  The microcontroller I used is a PIC18F2525, rather overpowered for this device but it's what I had.  All said and done, it's a $40 device with about the same features as the $1500 device you would buy from some company.

This was my first try at making a PCB, so it's only one layer.  It came out pretty well though and I will certainly use this method in future projects.  You can find instructions for making a PCB here.

This is the mask I used to make the PCB.  A printable PDF of this file can be downloaded here.

Circuit with parts labeled:

Click here for full-size image.  Sorry about being hard to read.

Parts List

If anyone is interested in actually building one of these things I will update this page with all the required details. Code to run the PIC is here.  This code could be improved, so if anyone is seriously interested in building this I will rewrite it all to make it faster and add options.