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I have built the following circuit to reset an AtTiny1614 (the mega tiny 1 series). They don't have a reset switch and I thought with this circuit I could (hard-)reset the chip by doing a power cycle.

Schematic

I've built the circuit (with the help of cheap Chinese pcb manufacture) and I measure around 1.7-3.6v between VDD and GND while pressing the button.

My questions:

  • Is the ATtiny receiving some kind of "parasitic" ground (sorry, I don't know the correct expression) from other pins that are pulled to ground?
  • Would the schematic work, if I would switch the misfet to a p-channel and use it on VDD? Or would there be some kind of "parasitic" 5V?
  • Any other suggestion on how I can power cycle the chip?
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  • \$\begingroup\$ Sorry, never heard of the AtTiny1516 (your schematic says 1614, haven't heard of it, either). A Datasheet link will be necessary. \$\endgroup\$ – Marcus Müller Nov 3 '19 at 12:55
  • \$\begingroup\$ Typo, it's 1614. Datasheet Link, for reference: ww1.microchip.com/downloads/en/DeviceDoc/… . They are "new". \$\endgroup\$ – Augunrik Nov 3 '19 at 13:46
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Disconnecting ground is, in most cases, not a good idea. To begin with why:

  • Instead of a "perfect" ground connection, your Attiny ground now runs through Q4. That's a recipe for noise and irregular behaviour. You seem to be using the ADC - not a good idea
  • The devices on the I²C bus will still define a potential for your I²C lines – disconnecting ground here is an especially bad idea

So, you'd really want to switch VDD in this situation. Of course, the decoupling capacitor will allow your attiny to run quite an undefined while after deconnecting.

So, really, reset your device usnig your device's reset. If your device doesn't have a reset pin, get a different one. Or one with a watchdog that you can reliably trigger.

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You can't reliably reset such a tiny microcontroller by just disconnecting power to the IC. It just needs a very small amount of current to keep its current state and restart from this position. Somewhere there was a report that even the photo-induced current by an LED connected to one of the pins is sufficient to keep the SRAM from losing its data.

Options you have:

  • use the dedicated reset on Pin 10
  • use the internal watchdog to reset the chip
  • do a reset by having your code write to the reset register
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  • \$\begingroup\$ Thanks for the list! \$\endgroup\$ – Augunrik Nov 3 '19 at 13:49

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