Prevent reset switch/button to be pushed again when device is running - Page 1
Forum section: electronics / beginners

author: samatthias
author_rank: Newbie
timestamp: January 29, 2020, 07:57:14 pm
content: Dear AllI have a very common - at least I thing it's very common problem. But I can't find any direct solution without a little bit of help from the great omniscient community.I would like to prevent the (hard) reset button/switch (mechanical) from being pushed again from a raspberry pi (the reset button has two separate pins on the rpi) when it's up and running (operating system is fully booted and properly running).Preferably I'm looking for a very simple circuit (no spi, i2c or any other fancy bus system involved) only a few components. My idea is a kind of "relay" - a normal relay is too large for this purpose - which is on in 0V state and off when I pull the GPIO high with 3.3 V on the RPI. The problem is, that I'm not a circuit designer myself so I have to look a around a nearly finished solution.Could anyone help me a little bit in which direction I should expand my research?I would appreciate you help very much!Best regards from SwitzerlandMatt

author: ebastler
author_rank: Super Contributor
timestamp: January 29, 2020, 08:32:11 pm
content: If you have a GPIO pin which defaults to 0V, and which you can set to 3.3V once the Raspberry is up and running -- can't you just use a pushbutton which connects this GPIO pin to the Reset input when pushed? Then it would pull the Reset input to 0V when the Pi is not ready yet, and will do nothing (by pulling Reset high) when the Pi has booted up.The part I don't get here is how you want to control power. If you have a separate power switch, the Pi will boot as soon as you power it up. In that case, why do you need the reset switch at all? Or do you plan to leave the Pi permanently powered, shut it down via software, then wake it up again via the reset button?

author: samatthias
author_rank: Newbie
timestamp: January 29, 2020, 08:41:20 pm
content: Hi ebastlerThanks for your answer. The "hard" reset pins are not on the normal GPIO header block - they are separate pins with 0V and 3.3V.And yes the system is totally haltet so either push the reset switch or disconnect the USB cable will reboot the rpi.I don't like the idea to pull and push the usb cable each time - because my application will automatically shutdown the rpi each time after a 15 min. inactivity (this is mainly because it's also powered by a usb power bank).Best regardsMatt

author: ebastler
author_rank: Super Contributor
timestamp: January 30, 2020, 06:22:27 am
content: Assuming that the Reset connector is still wired similar to the older Pi, it has one pin connected to GND, and the other connected to the Broadcom chip's reset input. (Plus some passive components, to pull the pin up to 3.3V under steady-state conditions and generate a power-on reset pulse.)See the "Dev Reset" connector shown on page 1 of the schematics, lower right:https://www.raspberrypi.org/app/uploads/2012/10/Raspberry-Pi-R2.0-Schematics-Issue2.2_027.pdfMy suggestion was to ignore the GND pin, and have a pushbutton connecting the other pin (Reset/Run input) with a GPIO pin of your choice. That should work, I think,ifthe GPIO pin really gets reset to be a 0V output when the system shuts down. And that's a big "if", I don't know how the GPIOs behave upon shutdown. If they become high-impedance inputs, for example, this simple reset idea would not work.Edit: Come to think of it, I am not sure what problem you are trying to solve here. The only function your reset button would have would be as a "power-on" switch, right? So why not simply mount it in an unobtrusive place, where it is not likely to be operated by accident once the Pi is running, and be done with it? After all, the mains switch in the back of any desktop computer isn't secured against switching it off while the computer is running either.