Hello,
I have a board that has onboard LiPo charging, I would like to implement a way to switch the board on and off, with the press of a button.
I'm designing a wearable, so I need the implementation to be as small as possible.
I've tried deep sleep, but it's not good enough, I need to be able to cut of power to the board entirely.
I can't use a button that has a physical latching circuit, because then I lose charging capabilities when the board is off.
Does anyone have any recommendations?
Thanks a lot for your time
Luke Belda de Vial
More soft latching circuit can be found with a search with Google or similar. Some variants that also lets your MCU switch off.
Just install a SPST switch in line with the board's positive wire.
If you put the switch after the battery - between the battery and the rest of the circuit - then it could still be charged when the switch is turned off.
Input power => charger => battery => switch => circuit load
But the board may not give you convenient access to that place to make a change. Do you have a link to the board you're using?
Hi ShermanP,
So this is the solution I'll try to implement.
Interestingly no board with onboard charging has these capabilities. At least not extremely small boards like the Seedstudio boards (all the Arduino boards are too big, even the nano's, for my application).
So I'm at a bit of a loss, the implementation you suggest is perfect, let the charging circuit have access to the power, and then have a switch between that and the rest of the components.
I've also looked into deep sleep, but I've found that when I go into deep sleep, the components attached to the board (mpu650) still draws power, it even has an led on, so I feel this option is not good enough.
Any suggestions are much appreciated!
Thanks to everyone who answered!
Yes, even if the main processor can be put to sleep, other parts of the circuit may not have that option.
In your first post, you said you have a board. Can you tell us which one that is?
You can actually have the MCU turn off other units, either power them direct from an IO pin, or with a FET in between.
I'm lookint at transitioning to the seedstudio esp32C3 board. For i't's size.
Right now i'm using the esp32c3 pico from Weemos.
The fact is i'll use any board that is really small, supports ble, lipo charging and is cheap.
Hi ledsyn,
I did not know this, i'll look into it.
Thanks!
I don't think any board is going to provide a way to add a switch, unless the designers specifically wanted to have that facility. But below are the relevant sections of the schematics for those two boards. In both cases the Vin pin points to where the switch would be. But you would have to be cutting traces and installing an external switch across the cut. I suspect everything is way too small to allow that.
But notice that both of the LDO regulators have a CE pin which is tied high. If the regulator is large enough you could lift that pin, and you could switch it between power and ground. The disabled regulator will still consume a little current, but the effect would be very close to a switch.
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