slow_rider
New Member
I need to control two latching relays using a single momentary SPST switch. Can anyone recomend a good & cheap way to do this? Maybe a DPST logic IC that can be controlled using the SPST switch?
Thanks!
Thanks!
Well from a concept basis a SPST momentary switch could be used to clock a flip-flop and the Q & Q-bar outputs of the flip-flop could be used to set and reset the single coil latching relay(s). The fact that you want both relays to operate together means electrically you could treat them as one relay. A SPDT momentary switch would be better because a simple pair of cross coupled NAND gates could be used for the logic with no contact bounce problems to deal with. Simplest of all would be a DPDT momentary center off switch would could be wired directly to the latching relay coil that would require no additional intermediate logic.I agree, some details were skipped!
I don't have an exact relay model but we are talking about signal type relays with a 4.5V or maybe 5V coils with a low current draw, 1 coil latching.
Both coils should switch at the same time, and your description is accurate, I want a single push of the SPST tactile to latch them and the second one to unlatch them.
I thought about this a little bit and I remember something called a multiplexer from logic class in university but I admit I forgot almost everything by now but maybe something like that could assist here?
A cross coupled nand gate operates (is the same) as a SR flip-flop. A type D flip flop can also be used as a SR flip-flop by using the direct set and reset inputs.Are you talking about an SR flip-flop?
The relay coil should wire to both the Q and Q-bar outputs, that is the polarity of the voltage applied to the coil must be reversed to switch the coil latch. You have to determine if the current capacity of the FF outputs can drive the coil directly or if you will need driver switching transistors to help supply the coil current requirements.I took a second look on the FF, and if I'm not mistaking a JK-FF could be used for this function.
I can hook J & K HI, when clicking on the tactile, CP will be set HI so Q(t+1) = Q-bar(t=0)
Hooking up Q to the relay will give positive voltage when I click, negative on the next and so on...
Is this correct?
Yes they come in IC packages. Here is a link to show how the various flip flops are designed and operate.Thanks for the help! Only one more question... any usefull links about how to actually build a JK-FF? Do they come in IC packages?
Nice circuit design KWith leftyretro's relay (5V/28mA, DPDT), I think this circuit will work. I've combined circuits that I've seen, but have not bench tested it. The paralleled outputs are to get enough current drive for the relay.
Ken