Capacitor for momentary switch?

Dear all,

I'm a complete novice at electronics and need help selecting a capacitor (I guess this is what I need).

I have a momentary switch that is wired to a controller board. The controller has a resolution of one second, in that it scans it's inputs once a second only. Sometimes when I push the button too fast, the controller misses it and doesn't register the input.

I'm hoping there is a way to connect a capacitor into the switch circuit so that it's held closed for longer than a second no matter how fast I push the button, and therefore registering the input on the controller without fail. I've measure 5VDC across the switching connection, incase that information helps.

Can anyone share a solution for this problem I'm having? ...and perhaps even suggest the right capacitor to use, if in fact a capacitor will solve this?

Many thanks, MrQuan

Reply to
MrQuan
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Capacitor wont do it -- you need a pulse stretcher, which may be more trouble than its worth.. you can make one with a 555 timer easy enough.. look for "one-shot" circuits where, when triggered, the circuit turns on for a specific period of time, then resets and waits for the next trigger.

Reply to
John Barrett

Using a toggle switch might work. Of course this may make operation a little goofy but it is better than it not working at all.

Reply to
EdV

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Since you know the controller\'s limitations, why not just hold the
switch down for longer than one second?
Reply to
John Fields

Well, that's fine for me in the workshop, but this solution was really aimed more at the people whos offices and buildings these are installed in. The controller is used for HVAC and access control. I have seen some of my colleagues label push buttons with "push and hold for one second", I was just hoping for a more elegant approach!

Reply to
MrQuan

I was actually looking at different switch alternatives, but I think for aesthetic reasons a push button style is my only option as it will be mounted to a small panel on a wall.

Reply to
MrQuan

I see how this solution would work, however as you say it looks like more trouble than it's worth... I'll have to look at alternative solutions I guess. I have been mounting neon indicators next to the push buttons, so the user gets feed back whether they have actually switched anything - and this seems to be working. I was just hoping, if it were easy enough, to make it totally robust. Thanks

Reply to
MrQuan

OK -- solution number 2 -- get a dual flip-flop chip (74LS74)... button hooks up to the Set line, which will "remember" the button press until the processor reads the data and deliberatly resets the flip-flop by pulsing the Reset line.. each chip will handle 2 buttons and no messy R/C timing needed.

Reply to
John Barrett

Then that is definitely the way you want to leave it - it protects the system from being turned on/off accidentally when somebody just bumps the button.

Cheers! Rich

Reply to
Rich Grise

Have the pushbutton set a flip flop and the sampler reset it.

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Many thanks,

Don Lancaster                          voice phone: (928)428-4073
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Reply to
Don Lancaster

There are ways to use an SCR to stretch your pulse. Might take 1-cap 2-resistors and an SCR. Off the top of my head. Mike

Reply to
amdx

I posted a schematic on alt.binaries.schematics.electronic of a circuit I used to debounce a switch, but I think you can modify it to stretch your pulse. Mike

Reply to
amdx

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