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

 

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.

 

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.

 

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!

 

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.

 

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

 

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.

 

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

 

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


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email:

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

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

 

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