Relay question

Chris Elmquist chrise at
Fri Nov 28 15:21:15 CST 2014

On Friday (11/28/2014 at 12:23PM -0800), Chuck Guzis wrote:
> On 11/27/2014 11:23 PM, Jim Brain wrote:
> I'm trying to wrap my mind around the problem.  Does this describe it?
> You want a push-on push-off circuit using only mechanical relays.
> Am I reading you correctly?

How 'bout this,

They show a 24V supply and relay coil but I see no reason a 12V supply
and coil couldn't be substituted.

The RC network is there to basically give you "opposite polarity" each
time you press the button.  It's charged to roughly the supply voltage
when the relay is unenergized and when you press the button, dumps that
into the coil to pull in the relay.

Then, while the relay is energized, the RC network decays to close to
0V and so when you press the button again, it pulls the topside of the
relay coil to 0V, dropping out the relay.

The RC network is the memory part of your "D flip-flop" :-)

You will need a DPDT relay though so that the other set of contacts can
control your load.

Chris Elmquist

More information about the cctalk mailing list