Momentary contact switched to latched state on/off?

SpaceDuck · Post by **SpaceDuck** » Fri Aug 14, 2009 11:41 am

I have some momentary contact pushbutton microswitches that are the perfect size and fit for my needs but my circuits should be using "regular on/off switches" instead. Did a lil searching on the web and it seems a common issue but so far I'm reading of multiple components being needed to accomplish this?

Would someone/anyone/you, care to share how this can be accomplished in the easiest manner?

Thanks in advance!

SpaceDuck · Post by **SpaceDuck** » Sat Aug 15, 2009 5:39 pm

Hmmm, stumped the electronic Gurus out there?

jwrjr · Post by **jwrjr** » Sat Aug 15, 2009 10:27 pm

That depends on whether the switch is directly controlling much power. If not, use a D-type flipflop wired to toggle (a 74hct74 should do well).

SpaceDuck · Post by **SpaceDuck** » Sun Aug 16, 2009 2:02 am

jwrjr wrote:That depends on whether the switch is directly controlling much power. If not, use a D-type flipflop wired to toggle (a 74hct74 should do well).

Under 12V?

jwrjr · Post by **jwrjr** » Sun Aug 16, 2009 12:48 pm

For 12v it would probably have to be a 4000-type D-type flipflop. I don't know what the part number would be. Just connect the /Q output to the D input, and connect the switch to the "clock" input. It will probably be necessary to connect the "clock" input to the power supply using a resistor (10k - 100k, value not critical) and to ground using a small capacitor (0.1uf is good). The reason for this is that mechanical switches' contacts "bounce" when you close the switch. The capacitor acts as a shock absorber. The resistor makes sure that the input is "high" until the switch pulls it down. Without the resistor the input floats, and you get a "maybe" Not good.

SpaceDuck · Post by **SpaceDuck** » Sun Aug 16, 2009 3:47 pm

jwrjr wrote:For 12v it would probably have to be a 4000-type D-type flipflop. I don't know what the part number would be. Just connect the /Q output to the D input, and connect the switch to the "clock" input. It will probably be necessary to connect the "clock" input to the power supply using a resistor (10k - 100k, value not critical) and to ground using a small capacitor (0.1uf is good). The reason for this is that mechanical switches' contacts "bounce" when you close the switch. The capacitor acts as a shock absorber. The resistor makes sure that the input is "high" until the switch pulls it down. Without the resistor the input floats, and you get a "maybe" Not good.

You echoed what I've read elsewhere about the "bounce factor" of a momentary switch trigger. But so far, the "other" schematics which seem similar, use a transistor/s, several caps and more. I'm in absoluetly no position to "judge" their suggestions but like always I am looking for the tidiest/easiest way out of course!

You may recall, you've always stepped up to assist in my quandries though it was quite a while ago so I do once again thank you.

So, how many chocolate chip cookies might it take for you to transfer that into a working schematic and parts list for me?

jwrjr · Post by **jwrjr** » Sun Aug 16, 2009 5:28 pm

I will see what I can do. Stay tuned ...

jwrjr · Post by **jwrjr** » Sun Aug 16, 2009 7:08 pm

Give me an address to send it to. I didn't make up a parts list as A. they are well identified on the schematic, B. with one exception are all non-critical, and C. all are as common as dirt. If you still need a list, tell me where you buy parts from and I will see about getting for you some part numbers.