switchestransistorsvoltage-regulator
I'm looking for a threshold switch which sets the output voltage to Vin, only when Vin > 5V and sets the output to zero otherwise.
I tried the circuit below but it does the opposite of what I want. It sets the Vnode1 = Vin when Vin < 5 and sets Vnode1 to almost zero otherwise.
How can I achieve the desired circuit?
Simplest circuit is by using a SCR (Silicon Controlled Rectifier), these are pretty common components, but not as common as transistors.
simulate this circuit – Schematic created using CircuitLab
To sound the alarm, it is enough to disconnect the gate from ground using the TRIGGER switch. A small current will flow through R1, to the gate and latch the SCR. Once an SCR is latched, it can only be reset by interrupting the current through it (by pressing the RESET switch).
You can replace a SCR with two BJT's:
I agree, a microcontroller would be the easiest, as you will need de-bouncing for your switch, and a state machine of some kind. There are other solutions, but they rapidly get more complicated. If you want to dabble in a tiny amount of programming, that is probably the solution for you. This dev kit is cheap, includes the programmer, and has access to enough pins for what you need. You would need to add a connector, and have an external circuit with a couple mosfets, a couple diodes, and a couple relays. Let us know whether this is a possibility for you, and I could draw it up in further detail.
If you wish to do it completely without SW, this is the process that you would have to go through to design a logic circuit to do it, where the clock would be replaced by a debounced version of your switch.
http://www.allaboutcircuits.com/textbook/digital/chpt-11/finite-state-machines/
Best Answer
something likethis perhaps.
simulate this circuit – Schematic created using CircuitLab