My question was asked a over 500 days ago by someone but was not fully answered; the poster may have given up or figured it out without telling us.

http://forum.allaboutcircuits.com/showthread.php?t=34515

I have the same question:
How can I use a 555 timer to create a polarity switching circuit from a 6 - 12v battery supply that switches every few minutes. For research purposes, I would like to be able to adjust the switching time between 5 or 10 seconds and a few minutes. Except for the switching block of the circuit there is only the battery pack and the output leads, which are connected to a couple rods. The rods get dirty (anodized) unless I manually switch the alligator clips every few minutes.

After looking at the great tutorials (the chapter on 555 timers and http://forum.allaboutcircuits.com/showthread.php?t=15342), I can see how an astable mode of the 555 circuit would work if I were switching between 0 and x volts. But with only a single output (pin 3) I am not seeing how to connect the electrodes to the 555 circuit.

My question may be as simple as, "What is the other pin number to connect my electrode to?" or it may be that I need a coordinated dual timer circuit or something...I hope not. I would also like to try this without a relay, if that is possible. I have looked at all I could of Bill Marsden's e-Books and posts regarding this.



Thanks in Advance,

Rob

 

Have your 555 circuit operate a DPST relay. The contacts can be rated for whatever current your probes use and can be criss-cross wired to flip polarity back and forth at the whim of the 555.

 

Rob,

The 556 dual timer can be used as a polarity switcher. I can send you a drawing, if you're interested.

 

Thank you Jaguarjoe for the DPST relay idea. I will try that if the 556 circuit doesn't meet my needs.

Yes, Skirmit, if you can post a 556 circuit that may work I can test it out this weekend.

Thank you both for such quick responses.

 

Rob,

The 556 dual timer can be used as a polarity switcher. I can send you a drawing, if you're interested.

Instead of sending it to him, how about posting it here? That way we all benefit, which is what forums are all about.

 

As you are familar with 555, just connect second 555 as invertor, ie tie pin 2 & 6 to pin 3 of first 555; connect rods to both pins 3.

 

Bernard,

Thank you for those clear and concise instructions. It will be until next week before I can try it, but I hear exactly what to do.

Thanks,

 

A nice post from magnet18, see pg. 9, Inverting Buffer: http://www.kpsec.freeuk.com/555timer.htm