Looking for a cheap way to sawtooth LED's

[rackoon]

Is there a cheap way to sawtooth LED's? 

I know I could get a controller board from suppliers for 29 to 44 bucks.

Heck, I bought some rope light for my son's room a few years back for $20, and it had a  dial for blinking, sawtooth, and constant.

I just want a simple manual way for my cab special effect lights to do somthning but stay on. 

[MonMotha]

If you're feeling all DIY, this is a great starter application for a microcontroller.  Something like an Arduino would make this pretty easy.  You may need some biggish transistors depending on how many LEDs you want to drive, but those would be the only external parts to most uC dev boards (other than a power supply, of course) needed.

There are also products like the LED-Wiz if you want a more "already built" type thing.

[Beretta]

well, cheapest way to interface to some leds would be using the printer port..

each data pin could handle about 20ma.. roughly 1 led.. otherwise you'd need to use a transistor.

im not sure how to go about it but you could get the saw effect using PWM (pulse width modulation).

[MonMotha]

Cycling the parallel port fast enough to introduce PWM effects without flicker is doable, but kinda CPU consuming.  The PWM will also have some variability that may be visible due to OS scheduling issues.

The programming in basically identical to what you'd be doing on a microcontroller, but you're using your PC's CPU and the parallel port for I/O.  Many microcontrollers actually have dedicated hardware for this (often referred to as an "output compare" unit or "PWM" support on their timers), so the program might actually consist of "set everything up then go to sleep".

Current ratings on PC parallel ports vary.  Most are good to 10-25mA sink, but may only be able to source 5-10mA.  You can use some transistors to increase this dramatically with very little complexity.  Of course, many PCs these days lack parallel ports entirely.

If you just wanted to turn them on and off, parallel port is nice and easy, but for PWM effects, it can get a little rough.  Certainly doable, but I'm guessing you've got better uses for those CPU cycles.