I'm building a PWM circuit based on Brian256's procooling article
here. So far so good, I've got a prototype set up on a universal breadboard to test everything and adjust it to my liking. I have run into one problem though. The rheostats I am using are 5K Ohm linear radioshack specials
. I assumed that the resistance would increase relatively steadily as the shaft is turned, but these rheostats go from 10 ohms to 5K Ohms in about 1/2 a turn of the shaft. Once the resistance reaches 5K it stays at that value for last 1/2 turn. So I am not able to throttle the fan using the full turn of the rheostat shaft, only about 3/8's of a turn. I have checked all three rheostats that I bought and they all have the same crappy characteristic. So my two questions are: Are all rheostats like this, it is a limitation of the design? And if not, could someone point me to someplace that sells higher quality ones? Thanks, hope I made sense
.