using 2 555 timers

Thread Starter


Joined Jan 4, 2011

I'm an artist working on adding some motion and lighting to a found object sculpture I'm building.

I want to switch 2 sets of LED's on and off in a manner that appears random. By modifying some plans I had found, I took 2 555 timers and had one flashing ~32 seconds and the other at ~43 seconds. When I put it all together with the relay it always flashed at the 32 second rate. Both timers were in sockets so if I pull one out I could get it to flash at 43 seconds, and of course if I pulled the other out it would clash at 32 seconds. But with both chips in the circuit it always flashed at 32 seconds.

The circuit below is what I am going to try to do next. The difference is that I added the 100uf cap at the beginning of the circuit, the .01uf caps between pins 1 and 8 of the timers, and the 10ohm resisters on pin 8 of the timers (as was suggested in a previous thread).

Before I unsolder everything and start over -- do you all think that this will work? Any comments or suggestions would be greatly appreciated!

Also, on my first try, the timers were right next to each other on the circuit board. I have a bigger project board, and am going to put them on each end with the relay in the middle. Thanks, again


Joined Nov 30, 2010
Reset is supposed to be "tied high". Connect the reset pins to the Vcc pins. Add .1uf capacitors from the CV pins to ground. These are stability devices because I can't see anything wrong with your theory.


Joined Feb 19, 2009
Using the negative going pulse on the "Out" may work better to engage the relay, though I'd suggest a MOSFET for the switch to control the LEDs, eliminates audible noise and reliability improves since you are removing a mechanical device.

I'm curious as to the delay times, 30 seconds is a long time to be looking at a piece of art, especially if the viewer is unaware anything will change. Maybe I need to sit in my art appreciation chair for a bit and think about it more.

Explaining the purpose of the lighting and random delays may help us create a better/more artsy/realistic random effect as well.


Joined Jul 1, 2008
If you don't put limiting resistors in series with the LEDs they're going to have an early demise. :eek: