Trigger switch using basic components

Question

I am doing a project at a local fair which is one of those 'steady hands' games. I am adding a twist that if you touch the wire with the loop you are dragging through it once, distractions will start.

Is it possible (using no ICs) to make a sort of trigger where when the loop touches, the trigger is triggered and the trigger output goes forever?

score 1 · Accepted Answer · answered Jun 30 '13 at 14:25

1

Yes. What you are describing sounds like a flip-flop. These are fundamental building blocks of digital circuits, and are available in great quantity at very low cost as ICs. It will be more expensive, and performance will be worse, to build them from discrete components. However, it can be done:

BJT flip-flop schematic

Pulling inputs E1 or E2 low will set or reset the outputs A1 and A2. You can see that if one transistor is on, it will turn the other off, so A1 is always the complement of A2.

answered Jun 30 '13 at 14:25

Phil Frost

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Thanks. Is that the same as bistable? – ultimatetechie Jun 30 '13 at 14:27
@user2442780 there are many things that could be described as "bistable", which just means it has two stable states. This circuit is bistable. – Phil Frost Jun 30 '13 at 14:29
is this circuit when turned on stays on even if the input is turned off? – ultimatetechie Jun 30 '13 at 14:30
@user2442780 that really depends on what you mean by "turned on" and "turned off". This isn't really the place to have a discussion about the circuit. You can always ask a new question. – Phil Frost Jun 30 '13 at 14:31
Shouldn't VEE be VCC :-) http://electronics.stackexchange.com/a/17384/2191 – RedGrittyBrick Jun 30 '13 at 20:20
@RedGrittyBrick yes, it should be. Blame Wikipedia. Or, maybe it was part of a PNP logic circuit that happened to have a section of NPN logic. – Phil Frost Jun 30 '13 at 20:48

Trigger switch using basic components

1 Answers1