straggler1
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5V pin on the pi zero and voltage monitor

Tue Jun 19, 2018 11:09 pm

I am wondering if the 5V pins on the Pi zero are directly connected to the micro usb power port. More specifically, if I was to connect a lipo battery to the micro USB port on the pi zero, does the 5V pin directly reflect the voltage coming directly from the battery? I have a ADS1115 I would like to use to measure the voltage on the battery so I can safely shut down the pi before it dies but I am not sure if I should monitor the voltage directly from the powerbank battery or is it ok to rely on the 5V pin for that use? If not, is there anywhere on the board I can solder on to as an alternative?

Thank you!

klricks
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Re: 5V pin on the pi zero and voltage monitor

Wed Jun 20, 2018 12:06 am

On RPi zero models, the micro USB power input and USB ports, and GPIO pins 2 & 4 are all connected directly together.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Stretch w/ Desktop OS.

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Imperf3kt
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Re: 5V pin on the pi zero and voltage monitor

Wed Jun 20, 2018 12:08 am

On all Pi models, the 5v GPIO pin is connected to the microUSB power input. pi zero models lack the polyfuse found in other models.

I doubt though, that what you want to do will work - a powerbank contains a boost converter. As the battery drains, the output voltage will remain ~5v until either the battery completely empties or some circuitry in the powerbank detects the battery is below ~2.9v and shuts off the 5v booster.
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straggler1
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Re: 5V pin on the pi zero and voltage monitor

Wed Jun 20, 2018 12:33 am

Thank you for your input. I didn't know about the zero not having the polyfuse. I attributed the lower voltage reading of 4.8-4.9 from the 5V pin to the fuse resistance. I also completely didn't even think that the powerboost in the powerbank would render the voltage regulation impossible. I might just use the 3.7 lipo with a boost and connect the ADC to the battery terminals prior to it getting through the powerboost and hopefully get the proper voltage that way.

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Imperf3kt
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Re: 5V pin on the pi zero and voltage monitor

Wed Jun 20, 2018 12:58 am

You could modify the powerbank in the same way, though I'm unsure about what happens when you recharge the battery.

There exist modules designed for the task though, such as the Adafruit 1000c or the DF Robot MP2636 (though this one requires some modification to access the pin on the MP2636 microchip which monitors the battery level)
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