[Pre-Order] Safe Shutdown Switch (PowerBoost Version) - Closed

[jsawhite]

@johweb You can try using another GPIO pin, or remove the dtoverlay line altogether and use UART BCM14 (Physical pin 8)

So is there any drawback to using pin 8 instead of a standard GPIO pin (with dtoverlay)? I like to keep my retropie setups simple (when I decide to rebuild) and one less step is one less step... But if it causes some other issue or problem, I can understand using the GPIO pin...

[Camble]

So is there any drawback to using pin 8 instead of a standard GPIO pin (with dtoverlay)? I like to keep my retropie setups simple (when I decide to rebuild) and one less step is one less step... But if it causes some other issue or problem, I can understand using the GPIO pin...

It takes a few seconds more to stabilise so you may not want to switch off during bootup.

[jsawhite]

ok, so I'm actually beginning to think my fet is bad... If I understand the circuit correctly, fet de-energized essentially closes en<->gnd. Switch on breaks the en<->gnd connection to power it on. Then the 3.3v from the pi (to keep-alive pin) energizes the fet essentially keeping the en<->gnd always open regardless of switch position. After the pi powers off, fet turns back off and closes en<->gnd shutting off power. Correct? So, in theory, if I tied keep-alive pin to 3.3v, once I turn the thing on, it should never turn back off until I disconnect power, right? That's what I did last night and as soon as I move switch to off, it drops power... It worked a few times when I first hooked it up, but then working became more and more sporadic. Now I can't seem to get it to work at all... Seems that the gate is blown? *shrug*

As the jfet should only be a couple of bucks from Mouser (and you're across the pond), can you let me which one you used? is it just a surface mount version of the 5460? Just want to make sure before I order...

[Camble]

@jsawhite Please disconnect from the PowerBoost and test the resistance between the EN and GND pins of the PCB with the switch in the OFF position.

Before you go buying replacement JFETs, I must warn you that I've had a huge problem getting ones which work, due to differences across brands (and I've even been sent counterfeits). I've looked at them on Mouser and you should be OK, as you'll get a genuine one.

[jsawhite]

@jsawhite Please disconnect from the PowerBoost and test the resistance between the EN and GND pins of the PCB with the switch in the OFF position.

Before you go buying replacement JFETs, I must warn you that I've had a huge problem getting ones which work, due to differences across brands (and I've even been sent counterfeits). I've looked at them on Mouser and you should be OK, as you'll get a genuine one.

I get about 400 ohms source to drain when I measured it... So that part is working. When I get home this evening (something about needing money and having to work... blah) I'll disconnect the en lead, and see what I get when it's energized... I'll update after that.

Thanks for the warning on the counterfeits... that sucks you had to deal with that...

Joe

[Camble]

@jsawhite Sounds like the JFET is fine

[jsawhite]

Just for testing purposes, I disconnected all the GPIO connections. Connected keep-alive directly to the 3.3V output on the pi, and pulled the SD card (so it never boots). In theory, once I turn it on, it should never turn off... I've taken some more measurements... Measured vs ground, I get 3.3V at the gate (expected). 0V at the drain (expected). 1.5V at the source (hmmm). Almost like it's not reaching full pinch voltage of the FET maybe? Or maybe the gate is blown? Maybe I'm not analyzing the circuit correctly (been a while since I'd taken my EET classes), but I wouldn't think it would drop half the voltage across it....

As it worked a couple of times at first, I'm assuming it was something I did. I won't ask you to do anything on this. I'll see if I can source another FET. I'll update more when I get one and replace it.

Thanks for the input.

[Pumpytums]

Hi,
does anyone know where to buy the switch that's on the safe shutdown please?

Ignore me found it

http://www.ebay.co.uk/itm/10pcs-On-On-2 ... SwKY9XiOcB

many thanks

[Camble]

Hi,
does anyone know where to buy the switch that's on the safe shutdown please?

Ignore me found it

http://www.ebay.co.uk/itm/10pcs-On-On-2 ... SwKY9XiOcB

many thanks

Just some additional information. That listing cites the model number as SK22H03. Most eBay listings do, but if you buy SK22H03 switches directly from a Chinese supplier, you will get switches with very large handles and supporting legs on all four corners. The correct model number is SK-22H07 (the hyphen is required to get any decent amount of results on aliexpress/alibaba)

[Pumpytums]

Thanks