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We use the attached circuit for some diagnostic timing prior to doing experiments. Basically when the momentary switch is closed, from a location away from the generator box, the left side of C2 is pulled up to ground from ~-6V and C2 can discharge through the oscilloscope. The goal is to have a battery powered box driven by a switch that can close without bounce.

It seems like a p-channel mosfet could act as the switch if the gate is driven to -9V. That solves the switching, but not the debounce issue. I need the switch to close somewhat quickly, <1us, so an RC debounce doesn't seem to make the most sense. I have used monostable multivibrators before but couldn't find much about getting them to output something like the ~-9 volts I would need to drive the p channel mosfet. Are there any simple solutions that I've overlooked or would a different type of switch make more sense? Pulse Generator

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  • \$\begingroup\$ See related: electronics.stackexchange.com/questions/41674/… \$\endgroup\$ – embedded.kyle Feb 22 '13 at 21:42
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    \$\begingroup\$ A 555 like timer should be able to go up to 9V. I've certainly seen schematics where its used to those ratings. You would have to check if there's a specific variant which supports that voltage. Aerospace applications typically operate at upwards of 12V, so something rated for that would work. That said, I don't see why a PMOS would need debouncing. Your control signal controlling the PMOS, if is a manual switch, would. But depending on your application and budget there are plenty of ways to do that. An MCU, a schottky gate with regular debouncing... \$\endgroup\$ – Chintalagiri Shashank Mar 1 '13 at 2:26
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Not all p-channel MOSFETS need a whopping -9V to turn on! Find one with a lower voltage.

As for negative voltage output from a monostable multivibrator, just take the standard monostable multivibrator circuit built from NPN transistors, invert the voltage supply and switch to PNP transistors.

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I would first use a debounce (maybe a schmitt trigger and a RC filter) to drive the input line of a MOSFET driver circuit. Once the MOSFET driver sees the "on," it can dump amps into the gate for a short while, to get it to turn on (or off.)

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