I have a bank of 5 DPDT momentary push button switches like the kind used
for preset frequencies on a car radio. I need a circuit with 5 outputs to
drive some relays such that when a button is pushed it latches the
corresponding output high and turns the other 4 off. This has got to be
fairly simple but I just can't figure out how to do it. Any suggestions?
yes, with that kind of switch you can do it.
on each switch you need to use the NC (normally close) contact on one side
to maintain a constant voltage to all relays on one of the NO (normally
So each Relay needs to be a DP, one pole for your use and the other
for the Loop lock to keep the relay in.
All the switches will be wired in series using this NC contact so that
when ever you press one, it will open the circuit at the end of the
string which is supplying the lock voltage on the contacts.
So just picture the lock voltage being connected to each (NO) contact
of each relay in parallel.
on the other side of the (NO) of each relay, you will connect one side
of it's own coil. This is where Coil will be getting it's energized
voltage from to hold it on. the other Coil connection will just be tied
to common along with the rest of the relays.
-- Now for the activation of the relay you want --
When you press a button, the (NC) contacts on the switch that is in
series with the rest of the (NC) contacts of the other switches will
open. this will cause loss of voltage in the remaining string of (NC)
contacts and which ever relay that was locked on will now release.
With the (NO) normally open contact of each switch, you will supply
to each coil power on the coil side connection of the relay..
remember i said the coil will be connected to the opposite side of
the locking contacts on each relay? this is where you connect your
momentary source to pull in the relay. when the relay pulls in, the
locking contacts will maintain it and with the mechanical slowness
of the relay returning, you should be able to release the button quick
enough to have it put the locking source back on before the relay pulls
If you find that the relay pulls back to soon? You can then use a
Cap on the output of each switch that energizes the relay coil going
to common to hold a charge. use a diode in series after that to feed
the relay coil.
The diode is to prevent the cap from being charged while the relay
is locked on so that it releases quickly, and only be charged from the
I don't have a ASCII translation program to use here otherwise, i would
have drawn it out for you.
personally, i would use Flip Flops with RESET and SET (RS) type.
The (NC) would force a Reset of all flip-flops with their RESETS tied
together, and the closer and opening of the NO contacts would be tied to
each Flip-flop's SET pin.
The Q outputs would reflect the state.
The RESET and SET pins need to be pull low to high to activate.
you would need small cap on the reset line to prevent debouncing.