Powering PYBv1.0 externally

The official pyboard running MicroPython.
This is the reference design and main target board for MicroPython.
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swp
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Powering PYBv1.0 externally

Post by swp » Thu May 01, 2014 4:16 pm

Hi,

Got my PYBv1.0 yesterday, very nice.

I'd like to know how to safely power the board from an external supply. I've seen Damien do this in his videos and it looks like the connectors next to the USB connector are the ones but I can't quite tell which.

They are labelled VIN, 3V3 and GND. My current guess is that I can put power between VIN and GND to power the board and 3V3 is an output rather than input.

Also what voltage range is safe to put in? Presumably 5V is ok as I can power it from USB.

Steve

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dhylands
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Re: Powering PYBv1.0 externally

Post by dhylands » Thu May 01, 2014 8:04 pm

Hi Steve,

The schematics for the board can be found here: https://github.com/micropython/pyboard/ ... YBv10b.pdf

When you plug in the USB cable, VBUS powers VIN (through D1 - a 1n5819 diode near the center right of the schematic), so you should definitely be able to provide 5V on VIN.
When the board is powered by VBUS, then VIN should be a diode drop lower that VBUS (looking at the datasheet for the 1N5819, the forward voltage is about 0.450V)
3.3v looks to be an output from U2 (bottom left corner of the schematic) which is an MCP1802 (aka a 3.3v regulator).

So I think you could also power the pyboard by providing a regulated 3.3v on the 3V3 pad, but then VIN would be unpowered for shields/add-on cards.
It also looks like the 3.3v regulator will work with any voltage larger than 3.5V (3.3V plus the 200mV dropout) all the way upto 10V.
So in theory, I think you could use a 9V battery, but I wouldn't recommend it (since its a linear regulator, anything above 3.3v is converted into heat, so you'd be wasting 2/3 of your battery on heat, and only 1/3 would be powering the board). It would be better to use an external switching regulator to get your battery down to 5V or even better 3.5v (depends on shield requirements).

Also be wary of cheap 5v wall warts. Many of these claim to provide 5v, but are often quite a bit higher.

VBAT is intended for a coin cell (typically 3v) to provide backup power for the onboard RTC.

Finally, if you didn't understand anything I just said, feel free to ask again, and I'll simplify.

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lurch
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Re: Powering PYBv1.0 externally

Post by lurch » Fri May 02, 2014 12:07 am

If you're not sure what you're doing, you can simply use one of those "emergency mobile phone powerpack" type things, e.g. http://www.amazon.co.uk/Ultra-Compact-L ... 005QI1A8C/ or http://raspi.tv/2013/pi-duration-tests- ... tery-packs

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andrew
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Re: Powering PYBv1.0 externally

Post by andrew » Sun Aug 10, 2014 6:49 pm

Or as I was hoping it looks like you can use a 3.7v LiPo rechargeable battery (http://www.adafruit.com/products/1317) on the vin + gnd pin:

https://www.youtube.com/watch?v=9joljCd-_8o

Andrew

varfare
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Re: Powering PYBv1.0 externally

Post by varfare » Thu Jun 04, 2015 6:43 pm

Sorry for digging an old thread but I have questions regarding this subject. Do I understand correctly posts above? If I'll connect 7.2V battery into VIN (pin to the right of microUSB port), pyboard will dump down the voltage to 3.3V internally but it will still output 7.2V on external peripherals' pins (such as VIN X1, X2, X3)?

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dhylands
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Re: Powering PYBv1.0 externally

Post by dhylands » Thu Jun 04, 2015 8:09 pm

varfare wrote:Sorry for digging an old thread but I have questions regarding this subject. Do I understand correctly posts above? If I'll connect 7.2V battery into VIN (pin to the right of microUSB port), pyboard will dump down the voltage to 3.3V internally but it will still output 7.2V on external peripherals' pins (such as VIN X1, X2, X3)?
Half right.

All of the signals like X1, X2, Y1, Y2., etc are always at 3.3v
The STM32F4 is 5v tolerant (can accept 5v in) if the pin is being used for digital purposes (GPIO, SPI, UART, I2C, CAN, etc) but is NOT 5v tolerant when used for analog purposes (ADC).

VIN is the only pin which will have more than 3.3v on it as an output.

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