[Guide] Graceful shutdown switch without Pololu [RETIRED]

[SidSilver]

Okay. Ill be using the Powerboost 1000c. Is there any way to get the battery status without aditional hardware?

The PowerBoost has an LBO pin which you can wire directly to a GPIO pin. The pin will go from 0v to battery voltage when the battery drops below 3.2v.

My circuit has a protective diode and resistor to ensure the voltage is below the safe 4.2v level for the GPIO pins, but this is superfluous as the LBO pin is only ever at battery voltage. Even if it was 5v (which it's not) it would only ever be for a short period of time.

Doesn't hurt to have it though.

https://learn.adafruit.com/adafruit-pow ... st/pinouts

@camble I thought the LBO pin went from battery voltage to low when the battery dropped below 3.2v. Also does the red LED on the Powerboost go on when you clamp the voltage of the LBO pin with the diode on your PCB? In my test it does.

I have not tested with diode but with 2 resistors as voltage divider, as soon as LBO is connected to GND the red led illuminates

[Camble]

@camble I thought the LBO pin went from battery voltage to low when the battery dropped below 3.2v. Also does the red LED on the Powerboost go on when you clamp the voltage of the LBO pin with the diode on your PCB? In my test it does.

Actually, yes. I made this mistake once. Popcorn corrected me. Then I made the same mistake

Anyway, the battery should never be above 4.2v and this is the agreed safe maximum for a GPIO pin (for short periods of time anyway)

@SidSilver That is because you are effectively pulling the pin to ground through the bottom resistor. Using a diode, you exploit the ~0.7v voltage drop to make the voltage safe.

[SidSilver]

@camble I thought the LBO pin went from battery voltage to low when the battery dropped below 3.2v. Also does the red LED on the Powerboost go on when you clamp the voltage of the LBO pin with the diode on your PCB? In my test it does.

Actually, yes. I made this mistake once. Popcorn corrected me. Then I made the same mistake

so your PCB will illuminate my powerboost red led ?

[Camble]

@SidSilver Shouldn't do, it doesn't pull the pin low.

[RxBrad]

So, I'm still trying to find a working JFET here in the US. The National-branded 2N5461 Jameco had listed ended up actually being another non-working Fairchild.

Hey, @Camble ... Is the Siliconix-branded FET you have pictured in the OP yours, and did it work? Thanks!

EDIT: Reread the post. Sounds like the pictured JFET works. Ordered this... Finger crossed...

[KrxXxiT]

Sorry to be a bother, but I'm not so good at reading electrical schematics and in your pic you're not using an original DMG switch.
From what I gathered, I made this simple diagram of how I interpreted the wiring to go. Does this look correct? And also, does 3.3v connect to the pi zero's gpio?

diagram.jpg (70.19 KiB) Viewed 7270 times

[hueblo]

Sorry to be a bother, but I'm not so good at reading electrical schematics and in your pic you're not using an original DMG switch.
From what I gathered, I made this simple diagram of how I interpreted the wiring to go. Does this look correct? And also, does 3.3v connect to the pi zero's gpio?
diagram.jpg

I posted one earlier in the thread the camble verified is correct. Hope it helps out.

[KrxXxiT]

@hueblo so you mean this one?
Does it work as it's supposed to with your schematic?

[Camble]

@KrxXxiT, that looks very close.

Make the following changes:

[RxBrad]

Psst @Camble.. I think you mean GPIO 27 in orange above. Not 17.