sudomod

awesome I cannot wait! I've been neglecting my retro gaming because I haven't been home enough to play. This is the best on the go solution yet!

@Camble
@Helder
I've been working on an emergency shutdown button for the banggood power supply on/off circuit. At first, I was thinking about just using a second button, but I have a different option. This turns the dual mosfet circuit into a triple mosfet circuit. It's a latching on/off, with a long press turning the system off. Also, the system will shut off if the Pi is not powered on within a couple seconds and it will also shut off a few seconds after the Pi powers down. So, the same button turns the system on, issues the shutdown command to the OS, and provides the emergency shutdown. Any thoughts?

Circuit is emulated here:
http://everycircuit.com/circuit/5301562995376128

The switch on the 3.3v supply represents the GPIO being pulled high or low with a 50kohm resistor, which I believe mimics the Pi.
Adjusting the capacitor nearest the output changes the time until power-off for emergency shutdown.

@othermod This circuit might interest you. A lot of the latching switch circuits I've seen have a long-press to shut the system off. I'd been looking at adding a reset button to my BangGood shutdown board, which uses a DPDT switch. There doesn't seem to be an easy way to do it without a normally closed tactile button, so I'd considered adding an RC delay to cover the possibility that the Pi hasn't shut down or has hung. I was hoping to get away with two MOSFETs though.

This video was very useful to me and I'm sure he mentions a long-press power off. He uses BJTs, but it's the same basic idea.

I've just started working on a psp as well and for the power button I was thinking about using the hold switch instead of the power switch for the power button since it's the latching kind. I figured it might be a bit more simple to setup that way.

Modesto Hagney wrote:I've just started working on a psp as well and for the power button I was thinking about using the hold switch instead of the power switch for the power button since it's the latching kind. I figured it might be a bit more simple to setup that way.

That's what I did initially, and it's definitely the easiest method. I changed it because the button is a little easy to bump and because it has to be switched off manually after the shutdown completes.

@Camble

Camble wrote: This circuit might interest you.

That's exactly the circuit I based the EveryCircuit design on. So the reason it has 3 FETs is because I am unsure whether the GPIO pin switches to GND when the shutdown completes, or if it is just pulled to GND with the internal 40kohm resistor. If it's switched, then the 3rd FET isn't needed and a diode will do the job of isolating the 3.3v from the 5v. If it's just pulled down with the internal resistor, then the circuit isn't pulled down far enough to switch the N-FET off. Any idea which way it functions?

Updated circuit:
http://everycircuit.com/circuit/5301562995376128

@othermod I'm not sure to be honest. The trouble I'm having is how to add an RC delay to my circuit with the DPDT switch. It should signal a shutdown, but also cut the power after 45 seconds for example. I'm not too great with capacitors, but I understand the general idea behind RC timers.

Camble wrote:@othermod I'm not sure to be honest. The trouble I'm having is how to add an RC delay to my circuit with the DPDT switch. It should signal a shutdown, but also cut the power after 45 seconds for example. I'm not too great with capacitors, but I understand the general idea behind RC timers.

@Camble
I'll do some tinkering to figure it out. Do you have a link to the DPDT circuit? I see this http://sudomod.com/forum/viewtopic.php?f=22&t=1059. Just making sure it's the one.

@othermod I don't have it on my just now, but it's not that circuit. It's effectively the same as yours for the PSP. I have an IRF7319 dual MOSFET in the same configuration. The only difference is that because it's a DPDT switch, it's like holding the power-button down forever. with the switch in the off state, it's as if you had a second push button to switch everything off.

Are you on Discord?

@Camble
Okay I understand now. You want some way to make sure it's going to power off regardless of the GPIO state when there is a problem with the OS. I am setting up a Discord account now.