Passive circuit for high side momentary switch with internal micro-controller pulldowns enabled

Good afternoon....Looking for a good simple de-bounce circuit using passive components.  I have multiple momentary high side switches connected to various micro-controller inputs that has pull-downs enabled.  There is some firmware de-bounce going on but I want to shore up the design with a simple analog circuit......All designs I've used and seen are for pulling pins low.  Does anyone have a good design for pulling pins high?Thanks

Hi Steve,I think a possible and quite easy solution would be to add an electrolitic capacitor across the momentary switch. When the momentary switch is not pressed, the capacitor charges. When the momentary switch is pressed, the capacitor discharges keeping high the microcontroller I/O. You should check the value of your pull-down resistor, considering that with a 10 kOhm pull-down resistor, a 10 uF capacitor can provide a debounce delay of 69 ms.
Best regards,Paul

Hi Paul....I  think that sounds like a good idea....I will most likely add a small resistor (1k) on the switch side that touches both the pull-down and the cap...That way when switch closes cap is directly shorted....The pull-down is anywhere from 20k  - 50k (MSP430FR series)....I think a ceramic 1uF should doThanks for the reply!Steve

I assume that you have the switch connected to the power supply so why can't you just invert the power supply and ground connections on the circuits you've found?As Paul points out, a capacitor across the switch might work although I'd rather use a ceramic than an electrolytic unless you need really long delays. A design that I'm working on uses an RC circuit followed by a schmitt-trigger buffer for this application.

There is an interesting document  here, and EE ran a series on the topic, part one of 8 starts here.The switch can be high or low side, you just have to be aware of polarised components, like diodes, if used.Cheers,Richard

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