dimming hid’s

PWM = Pulse Width Modulation

PWM is a digital technique used to control how much power is sent to a device.  It, in essence, is a duty cycle controller (duty cycle = on / off ratio). 

Say, for instance, you wanted to dim an LED.  You could do it with analog current through a potentiometer or you could do it digitally with PWM by creating a period (say 1khz - 0.0010 seconds) and then controlling how long power is on inside the period.  If you want the LED to be at ~50% brightness you would supply power for the first 0.0005 seconds and then turn the output off for the remaining 0.0005 seconds.  At the end of the period you start over.  For 100%, the on time would be .001 seconds and the off time would be 0.000 seconds, 75% would be .00075s on and 0.00025s off and so on and so on.

PWM can be achieved using a small 8 pin microcontroller and a few lines of code.

Interestingly enough, you can NOT PWM LEDs on a rotational blade.  I found this out the hard way after building a dimmable night blade controller for a remote control hellicopter.  The constant high speed rotating basically turns the pulse width modulated LEDs in to a pie chart that somewhat illustrates the duty cycle.

A 555?  What's that?   :)

Years back I got in to Atmel controllers and I've never used anything else.  You can build a parallel port programmer for $3.  You can download the AVR studio program free and you can download PonyProg to flash the chips for free.  You'll spend $2 on a controller.  So, in all, you'll have $5 in "start up" costs.  I doubt you'll find anything cheaper then that.