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complete electronics novice here unfortunately. Please bear with me.

I'm after some kind of switch (latch/flip-flop?) that will interrupt a momentary switch held in its 'on' position when another momentary 'reset' switch is pressed but also requires the 'on' switch to be released and then pressed again before triggering. This is to control a motor that is currently driven by a mosfet circuit so I'm just after a logic level signal to feed into it.

e.g 'on' switch held -> motor starts -> 'reset' button pressed whilst 'on' switch still held -> motor stops -> 'on' switch still held -> motor still stopped -> 'on' switch released and then held again -> motor starts

I apologise in advance for the total lack of terminology. If I can just get pointed in the general direction of something it would be greatly appreciated.

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  • \$\begingroup\$ Just a precisation: a JK latch doesn't exist, they only are flipflops, i.e. synchronout to the clock. Maybe you mean an SR latch, which is almost the same but has an anomalous reaction on both the inputs driven. Neither will do what you want, people already answered on that. \$\endgroup\$ – Lorenzo Marcantonio Mar 30 at 6:21
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If you want to use relays, this should work: -

schematic

simulate this circuit – Schematic created using CircuitLab

So when you press start and hold it, the supply is routed to the motor via the relay NC contact and the motor spins. If whilst holding the start button the reset button gets pressed momentarily, the relay latches the "reset event" because the relay contact then shorts out the reset button. And, at that very instant, the motor is disconnected from the supply.

Not until the start button is released can the relay/latch be unlatched and then, the whole cycle is back to the beginning.

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  • \$\begingroup\$ I can't seem to identify the latching (in a flip-flop sense) behaviour in this circuit. Although the OP does not really specify where and what to latch, mentions only momentary switches and that it is controlled via a mosfet perhaps there is not supposed to be any latching behaviour. Maybe I'm just confused with the the use of the word latching when actually no real latching behaviour is desired. \$\endgroup\$ – Pau Coma Ramirez Mar 30 at 7:23
  • \$\begingroup\$ I mean yes, as long as the start button is maintained pressed, toggling the reset button does latch the circuit.. but only as long as as the "start" button is maintained pressed, guess I am just confused by calling the button start. I would call it run. \$\endgroup\$ – Pau Coma Ramirez Mar 30 at 7:31
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This will do what you have asked for, assuming it is OK to use logic ICs. This can alternately be implemented using relays. Let me know if you need that instead.

schematic

simulate this circuit – Schematic created using CircuitLab

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