[Guide] Graceful shutdown switch without Pololu [RETIRED]

[Camble]

@RxBrad Sounds like you have a similar issue to @Popcorn. He is using a Motorola brand 2N5460 JFET and it just doesn't seem to like him.

Going back through the thread, it appears that @Popcorn eventually got it working... I wonder how he managed that?

So far, my Fairchild-branded JFET (purchased from Jameco) appears to be a no-go.

Popcorn knows my feelings on the circuit he finally used. By all accounts, it shouldn't work the way he has it set up.

[fdeluxe]

Stupid question: What are the downsides of not using a graceful shutdown switch? I'll have to shutdown the manually to prevent filesystem corruption?

[Ganreizu]

Stupid question: What are the downsides of not using a graceful shutdown switch? I'll have to shutdown the manually to prevent filesystem corruption?

Yes. If you don't know when the battery will die it won't shut down safely.

[RxBrad]

So, do we know which brands of JFETs work for this switch?

It sounds like Fairchild and Motorola do NOT.

I've found a National brand one here, but not sure if it'll work... EDIT: Warning.. I ordered this and received yet another batch of Fairchild-branded JFETS that don't work. Don't waste your time on them.

[HoolyHoo]

I think the problem with the JFET's is that there is variance with the tolerance on the pinch off voltage even among same brands. So some might work while others do not.

[RxBrad]

Hey, @Camble.. I was going to try building the non-DMG version of the switch, and noticed that you have the schematic for it labeled Obsolete on the first post. Do you have the current schematic for this switch anywhere by chance? I only see a revised version for the DMG. Thanks!

[Camble]

@RxBrad The second schematic will work for both switches so I recommend ignoring the first schematic.

That brand JFET should work. I'm using the surface mount version for my boards.

[fdeluxe]

Stupid question: What are the downsides of not using a graceful shutdown switch? I'll have to shutdown the manually to prevent filesystem corruption?

Yes. If you don't know when the battery will die it won't shut down safely.

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

[Camble]

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 LOW when the battery voltage falls below 3.2v.

My circuit has a protective diode and resistor to ensure the voltage is below the safe level for the GPIO pins, but this is superfluous as the LBO pin is only ever at battery voltage.

Doesn't hurt to have it though.

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

[HoolyHoo]

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.