I have a product, and I would like to have a way for the user to do a hard reset as a last resort.
The device is permanently powered, and spends most of its life in power down sleep mode, but the user can't disconnect the battery without a screwdriver and a soldering iron.
There are four push button switches, which are connected as shown, all four being read by a single ADC input. This works fine.
I was considering the attached circuit for an emergency reset, whereby the right hand switch is held depressed for some lengthy period, discharges the cap through R7 and D2 and forces a reset. When the switch is open, the cap can recharge fairly quickly via R1, R2, R6 and D1.
Values of R6, R7 and C1 are guesswork at this stage.
This may, or may not have worked. I never got as far as testing it because I noticed a big diptera in the viscous topical medication, namely the internal resistor in the ATTiny44A reset circuit, that has a minimum equivalent value of 30K.
So, unless anyone has a bright idea as to how to circumvent this(bearing in mind that I have virtually no PCB real estate left and a tiny[sub microamp] power budget), I will have to re-think.
A while ago I received an email flyer from somewhere containing details of special chips that do this sort of thing for the Kindle, for example. Dedicated circuits that will respond to a very lengthy button press by issuing a reset.
Typically, I deleted it, and now I have searched in vain for any reference to such a device.
Anyone seen these?