Toggle state between two circuits with two momentary switches

Question

I have two circuits each with their own 1.5v power supply. I would like to toggle state between the two circuits with a switch, so that hitting a momentary switch turns the light off on one and turns the light on on the other. I've been able to wire in the momentary switch on each circuit but I need them to toggle each other.

I've looked into flip-flops but I'm a bit lost and haven't been able to figure out the best way to connect the two independent circuits. No code, this needs to be done with discrete components.

Sorry if this is a stupid question, I'm still learning the basics. Thanks for any tips/pointers.

Answer 1

What you need to build is called a Bistable Multivibrator. Basically with a pulse as applied, the circuit will toggle from one state to the other.

With multivibrator circuits, you can have two output - one being the inversion of the other. With such an arrangement, you could then use something like an optocoupler to connect each output to one of the "black box" circuits.

Interestingly, this is exactly what a flip-flop is. If you get a D-type flip-flop with Q and !Q outputs, all you need to do is wire the D input to the !Q output, and connect your push button to the clock input. Finally you connect the Q an d !Q outputs to the two optocouplers which are then connected to your boards.

To improve things, you'll also need some debouncing on the push button to avoid multiple clock pulses. This can be done using an R-C circuit and a Schmitt trigger to generate a nice clock pulse from the push button.

I can draw up a circuit if that is easier to follow.

Answer 2

If it works on each circuit independently you could always use a NOT gate to switch the logic for the 2nd circuit. This may not be useful information, maybe I could clarify if you provided a simple schematic?

Answer 3

I am being naive I think. Hope you have heard of DPDT switch. Dual pole dual throw switch. You can use it and close the issue. Terminal A,B,C,D of DPDT can be wired in this way. A goes to Ckt1 Q6, B is open. C is open. D goes to Ckt2 Q6. P and Q terminals are connected to Ckt1 Q7 and Ckt2 Q7. When the DPDT is in one state, circuit one will be closed, and when the DPDT is in another state the circuit 2 will be closed.

A----o

   o---------- P

B----o



C----o

   o---------- Q

D----o

P and Q both operate together.both can move up or down together. When P contacts A, Q contacts C. When P contacts B , Q contacts D. These switches are easily available for purchase.

Answer 4

There seems to be an inherent problem with the circuit in that if both LEDs come up OFF on power up, then subsequent simultaneous toggling will keep them locked in phase unless the symmetry is somehow broken.

On power-up in the schematic below, U1-RST is held momentarily low by the integrator R3C2, which forces U1-OUT low while the power supply output comes up to voltage. Also, U1's TRIG input is held high by the network R1R2C1D1, further insuring that U1-OUT will stay quiescently low.

C5R5 is a differentiator, and is used to drive one of the inputs and the output of U2 high for a short time after power-up, that pulse being used to ensure that the LED associated with ASIC 1 (not shown) will be ON after power-up, while the LED associated with ASIC2 will not.

Thereafter, whenever S1 or S2 is made, a short,low-going edge will be presented to U1-TRIG, which will start the timer and cause its output to send a high-going pulse to K2 and to k1 through U2. that pulse will cause K1 and K2's contacts to close momentarily, which will cause the ASIC LEDs to toggle, with ASIC1's LED turning off and ASIC2's LED turning on.

Later, if either S1 or s2 are made another pulse will be generated which will toggle the LEDs back to their starting state, and the cycle will begin anew.

K1 and K2 are shown as relays, but could just as easily be analog switches if their ON resistances were low enough for the ASICs to accept as valid "contact closures".

In the meantime, if you'd like to play around with the cicuit, here's the .asc file:

Version 4
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