Push Button Selector Switch (No ICs)

Thread Starter

iimagine

Joined Dec 20, 2010
388
So I got bored and decided to see if i can come up with a circuit that can have multiple switches and only turn on the one that is selected. Only one switch can be on; push button style.
I came up with a working circuit, it simulates well. I'm posting it to see what everyone think.

DeleteMe.PNG

Description:
Yellow box: One shot circuit
Blue box: Latch on
When a button is press, a quick one shot pulse is fired and resets all switches to off, leaving only the one thats being pressed on. Can have as many buttons as you want :)
 

RPLaJeunesse

Joined Jul 29, 2018
62
When one considers real-world leakage (collector-base, PCB, source-drain, etc.) at higher temperatures you may find your resistor values are excessively high, especially the 10M one. The BJT might need a pullup on the emitter.
 

crutschow

Joined Mar 14, 2008
23,348
It's an interesting design exercise, but generally too complicated and expensive to build versus much simpler circuits using ICs.
 

Alec_t

Joined Sep 17, 2013
10,362
Interesting. Does the circuit have any advantage over the more common simple 2-transistor latch?
 

RPLaJeunesse

Joined Jul 29, 2018
62
Implemented in a way that is extendable to more than 2 selections, it is a 2-transistor latch, albeit per switch. The logic term for such an implementation is "one hot" coding.
 

RPLaJeunesse

Joined Jul 29, 2018
62
Looks like it should work, provided the supply voltage is well above the sum of Vgs(on)(PMOS) + Vgs(on)(NMOS). Otherwisewhile a switch is closed saturated switching might not occur.
 
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