vcc in and out?

[espruino-discuss3]

Posted at 2014-11-13 by d0773d

I know the espruino can be powered by usb and battery. Is there a vcc in? Also Is vcc out that supports 5v?

[espruino-discuss3]

Posted at 2014-11-13 by DrAzzy

You can power it by supplying power to the VBat pin, though this will bypass the fet and self-resetting fuse, and unless it's being supplied with 5v or more, don't plug USB into it (see http://www.espruino.com/EspruinoBoard power section). It's probably better to pipe in external power through the battery connector for this reason.

You can get power off of the VBat pins (at whatever voltage is supplied, 4.7 if powered at 5v over USB, due to drop across the diode), or the 3.3 pin (at 3.3 volts, ofc).

If you're powering it off of 5v, you can get 5v from the VBat pins (the 4.7 when on USB is enough to run stuff expecting 5, in almost all cases). Otherwise, there's no source of 5v on the board - it's only got the one regulator to provide 3.3v to run the chip.

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Posted at 2014-12-12 by Hellis

Sorry to dig up an old thread.

But what happens if you power the Espruino with, say 4 v and plug in the USB cable?
Will it be a different outcome if you use the batteryconnector or pins on the board?

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Posted at 2014-12-12 by @gfwilliams

Hi Hellis,

When you plug in USB, that'd take over - so the voltage on the pins marked 'Bat' will be 4.7v (5v minus the diode's voltage drop). Then when you unplug it, the battery voltage will take over (with no diode voltage drop) giving you 4v.

The pins marked 'Bat' are different to the JST connector though. Basically the 'Bat' pins are the voltage after it's been through the smart switchover between USB and battery - so only connect a battery via the JST connector. If you connect it to 'Bat' then it'll get charged up to 4.7v (which is almost certainly not what you want :) )

There's more info, including a circuit diagram, under the 'power' heading on this page.

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Posted at 2014-12-12 by Hellis

So just to make sure I got it correct.
Nothing 'bad' will happen with the Espruino, but in case you have something connected that does not like higher voltage that part will/might be affected.

The reason I wonder is because I can't use the batteryconnector because it's blocked by the case.
So either I use the pins or the backside of the batteryconnector. But that looks hard to solder on. Probably nothing I should even attempt :-)

I tested using two CR 2025 (I think it was) to power the board on the pins and it worked fine.
But as they run low the voltage will drop below 5 volts, and that was my concern, that it could dammage the board.

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Posted at 2014-12-12 by @gfwilliams

Yes, that's about it. However if the CR2025s go below 4.7v then when you plug in USB it'll try and charge them, which probably isn't good.

If you added a schottky diode (so you only get a 0.3v voltage drop) between the battery and 'Bat' it'd be totally safe though.

One other thing - if you're doing this for yourself then you might be able to modify a JST battery connector so the wires came out of the top, allowing you to fit it even when the Espruino was in a box. It'd be tight though.

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Posted at 2014-12-13 by Hellis

Charging CR batteries seems like a bad idea.
I'm "new" to electronics, the reason for a schottky diode vs. a normal diode is that it's faster and has a lower voltage drop?
A schottky diode is very cheap to buy, found one type that cost £0.07 but shipping it cost £3.

So until the next time I place a order there, can a normal diode work?
The obvious problem is that voltage will drop below 4.7v quicker with a normal diode than a schottky diode.

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Posted at 2014-12-13 by DrAzzy

Yeah, we just use the schottky diodes because of the lower voltage drop.

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Posted at 2014-12-13 by Hellis

Thanks!