I'm trying to modify this circuit to take a 3.6v-4.5v source (3 AAA), while powering 4 LED's in the same fade pattern. From what I've read, the only thing I need to change is the resistor before the LED's, the rest of the components effect timing. I will be using a variable resistor for manual timing. What I want to do is make the LED's throb, but never completely go off. I'm hoping the variable resistor will do something to this effect, but i have a feeling it will only control the speed between fades. Will a cap located infront of the power limiting resistor for the LED's achieve this (bottom right on diagram)? And of so, any idea what rating I need? I'm also going to try to bypass this circuit with a switch, which will power the LED's directly from the source .. but with a flashing LED leading. That way the the normal LED's will also strobe. I may need help with this part later. Sound feasible in theory? Original: Website: http://www.metku.net/index.html?sect=view&n=1&path=mods/colorfade/index_eng Which was taken from "Fading red eyes" here: http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm
The easy way to stop the leds from going completely off is to raise the trough of the triangle-wave, replacing the two 47k resistors with a pot, a bit like this. However, trying to run the circuit from below 5V is dodgy. The LM324 loses at least 1.5V and the transistor another 0.7V, so on 5V you've only a possible 2.8V peak for the maximum led supply, so it's almost certain to dim right off as the triangle-wave dips down below 2V. A 9V battery will give better control.
Thanks for the reply. I think I may look into PIC programming. WIll I have the same problem using a pic setup with only using 3x AAA batteries as the source? I looked into the 2016 3v cells as well as various 9v batteries. None of which have enough mah to run 4 superbright LED"s for very long.
It's not hard to use an LM324 to make a PWM led throbber. The IC is 3V minimum supply, so it should run OK on 3xAA cells. This worked for 12V but will maybe need some redesign for lower voltages.
