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Topic: Using a Normally-Closed Switch to Reset Arduino (Read 998 times) previous topic - next topic


Hi, I have an arduino Uno that I would like to reset using a normally closed switch, rather than the normal normally-open one. The reason is that I want to reset the arduino when a cable is pulled (the same cable sends power and data to an external chip which must be syncronized)

The arduino has a 10k pullup resistor on the reset pin, and I believe the atmega328 also has an internal pull-up. So, I was thinking that I would have to put a stronger pull-down resistor, say, 1k, to gnd and then have a connection to Vcc going through the cable. Would this work? Are there any other possibilities?

Thank you!


a 1K 'pull down' should work just fine. As 1 K and 10K in a potential divider would leave the reset pin at around half a volt, well below the 2.5 volt threshold.

It would however mean that you were burning 5mA through the resistor all the time.

A 4k7 resistor should work fine too, and that way you'd only be burning an extra 1 mA.
I write books about Arduino and Electronics: http://simonmonk.org


How would a 1uF capacitor with one end on the reset line and the other getting pulled to ground when the switch is closed work? That's how the DTR auto-reset works.

Slightly unrelated, does it matter if it's .1uF or 1uF on the auto-reset for uploading code? Or does the speed of resetting matter?

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