# Persistent Bistate Toggle Switch

I'm a noob if it comes to electronic components but I'm trying to achieve the following and I would really appreciate some suggestions:

I have the following requirement:

1. When a circuit is closed the first time (via some sort of pulse switch), an LED will receive power.
2. After the circuit is closed the first time, it will be open again for a long duration of time.
3. When a circuit is closed the second time, LED should not receive any power.
4. Loop continues 1-3

Basically I want a pulse of electricity to toggle circuit on every other time. Note that during the off state, the circuit will have no power at all. So any solutions involving 555 timers etc won't work.

I have bee reading about Dual Coil Bistable relays and I was thinking to use it in conjunction with some logic gates to make this happen, but I feel like I'm going a little bit too far with this and maybe this is simpler than I make it.

Thank you!

• What is the voltage of the power source? Is using a coin cell battery an option to place the control circuitry in standby, Jul 3, 2019 at 10:33
• Use a D flip-flop set up as a Toggle feeding a 555 timer set up as a one shot. Jul 3, 2019 at 16:46
• The name of the circuit you're looking for is 'T flip-flop'
– SF.
Jul 28, 2020 at 5:18

Good news, this is much simpler than you're making it out to be.

You simply want an On-Off-On-Off alternating Toggle Switch, like this one: https://www.adafruit.com/product/1684

Connect your LED to only one of the outputs, and away you go.

EDIT: I just spotted that you want to trigger this with a pulse of electricity, not a button push (I misread 'pulse switch' as 'push switch').

Given that you want this to be reliable when there is no power at all in the system, I'd still use a mechanical toggle system like this - simply set up a small solenoid actuator to push the switch when you send the appropriate pulse of electricity.

If you are using a power-down of the whole system as the 'off' state, you may be able to go with a simple On-On Alternating toggle, or SPDT switch, although this will flash the LED for a short time at the start of point 3. while the solenoid switches the LED off.

• Your solution would definitely work. I think it's a bit too mechanical for me though since my application is very small ( a wall clock and I need to hide the circuit behind it). A T-Flip Flop is what I'm after but if I'm not mistaking, most ICs like MC74HC73 need constant power to it to maintain those states after power off? Jul 5, 2019 at 14:32
• Add a battery! Make it a rechargeable if you need to top it up, too. Jul 6, 2019 at 9:10
• (But you can definitely find tiny solenoid actuators and switches - my original idea might not as large as you think, and would certainly fit behind every wall clock I’ve ever owned) Jul 6, 2019 at 9:12

H would have to be your switch. You may have to use switch debounce.

Use $$Q$$ or $$\bar Q$$ as required to get triggering as required.

Adjust 1kΩ and 10μF to get LED to function as you want. Little unclear how it works between your 1. & 2.

out goes to LED

Falsted simulation T flip-flop triggering 555 one-shot

• This looks great! More elegant, but perhaps less satisfying than a solenoid punching a big clunky button ;) How does this circuit react when completely powered down? The LED seems to only pulse on for a short time, it's unclear if this is OP's design intent? Jul 4, 2019 at 7:50
• OP 1 & 2 are unclear. Not a true solution, but it does give OP options. Jul 4, 2019 at 12:43
• Thank you for your answer; however, I don't think this will function in complete no-power situation? Meaning 555 timer power is cutoff and brought back up? I think I need exactly this: falstad.com/circuit/… but not sure how to make it happen. Jul 5, 2019 at 14:29