Making a momentary switch into a latching switch

[2camjohn]

Hey all...

I wanted to swap a latching switch i am using in one of my circuits, for a nicer, cheaper momentary one.
Im having some problems figuring out what IC to use for the latching function.

There are no current requirements, it just has to output a signal. But it has to work off 12V.

There are alot of bi stable ICs out there at good prices, but they all seem to have a separate input for set and reset.

What I want is to use the one momentary input (from the switch) to toggle the output between high and low.

Would I be correct in assuming you cant just connect the set and reset inputs together, to get a single input bistable operation out of something like a d type flip flop?

Can anyone suggest an IC that I should look at for doing this?
Or should i be looking at more generic logic for acheiving this.


I dont really want to use a micro, just because of the lower supply voltage and complexity of programming it before soldering.
But if it gets to the point where the IC and associated debounce circuitry becomes as complex as programming an micro (which at least can perform simple dedicated timing operations like debounce) then I will do it that way.

 

[Leftyretro]

"Would I be correct in assuming you cant just connect the set and reset inputs together, to get a single input bistable operation out of something like a d type flip flop?"

There are several methods to use either simple gates, cross wired, to convert a momentary switch to a latched state. Also a D type FF would work fine. Issues to be considered are what contacts do you have available on the new switch? SPDT would be the best choice and require fewer passive components. Also you need to determine how to deal with the power up state of the latch circuit as you most likely don't wish for a random on or off state on initial powering of the circuit. An R/C connected to the direct reset pin on a FF can force a initial reset state.

Today a more elegant solution is an inexpensive 8 pin PIC. With proper programming it can deal with switch contact bounce, initial output state and other tasks that would take more components to duplicate. Say you wished to have the momentary switch create pulse outputs if held down for longer then say 3 seconds as well as simply toggling otherwise, again simple with a 8
pin PIC.

Lefty

 

[Boncuk]

Today a more elegant solution is an inexpensive 8 pin PIC. With proper programming it can deal with switch contact bounce, initial output state and other tasks that would take more components to duplicate. Say you wished to have the momentary switch create pulse outputs if held down for longer then say 3 seconds as well as simply toggling otherwise, again simple with a 8 pin PIC.

Lefty

E.g. MAX16054 (SOT23-6 package) It toggles on - off - on. Two outputs Q and /Q. With an RC-circuit connected to the clear input it generates pulses. Power on-reset always low output.

Hans