mlepage
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Re-routing PWR IN on Zero W

Mon Feb 12, 2018 1:07 am

I have a Zero W and an Adafruit PowerBoost 1000C. I want to use the PowerBoost with a battery to power the Pi (and charge it) but I want to use the original PWR IN microusb on the Pi, instead of the microusb power in on the PowerBoost.

That is, I want power to go from the power supply to the Pi power jack to the PowerBoost power jack, then split to the battery and back to the Pi (via PP1 and PP6). The only thing out of the ordinary in this scenario is using the Pi's microusb as part of the route to get to the PowerBoost.

Is there anywhere on the Zero W I could cut a trace or remove a resistor or something to interrupt the flow of power from the microusb PWR IN to the rest of the Pi (and instead re-route to the PowerBoost)? Otherwise, I'd have to lift the +5V pin on that microusb, and that looks tricky (probably have to desolder the entire jack).

[The reason I want to reuse the Pi's jack, is I want access to all three jacks (power, USB OTG, and mini HDMI) and I don't really have room to put the PowerBoost there as well, so I'd like to locate it elsewhere in my limited space.]

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OutoftheBOTS
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Re: Re-routing PWR IN on Zero W

Mon Feb 12, 2018 9:40 pm

You can power the RPi from any of the 5v pins on the GPIO header they r just a common rail with the power usb connector on the RPi zero.

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Imperf3kt
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Re: Re-routing PWR IN on Zero W

Mon Feb 12, 2018 11:39 pm

OutoftheBOTS wrote:
Mon Feb 12, 2018 9:40 pm
You can power the RPi from any of the 5v pins on the GPIO header they r just a common rail with the power usb connector on the RPi zero.

Not what the user wants.
They want to use the USB connection as the power in but route that to an Adafruit 1000c first, then back to the zero.

You could probably cut thr trace and solder it like you expect, but beware soldering traces is extremely hard (at least for me)
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Re: Re-routing PWR IN on Zero W

Tue Feb 13, 2018 11:42 am

I would say this is not realistically possible, as any points were you could possibly disconnect the incoming 5v would be to small to work on using hobbyist soldering kit.
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mlepage
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Re: Re-routing PWR IN on Zero W

Wed Feb 14, 2018 12:04 am

I have soldered tiny stuff at work. We have a USB microscope, fine tip soldering iron, etc.

What I'm most concerned with, is where is the best place to do it? Is there a specific resistor/capacitor I could disconnect? (I can't find a specific schematic for the Zero W.) I don't really see the trace coming from USB PWR IN 5V, so I assume it rabbits into the board right away. And looking at the abridged schematic on this site, it seems like it might split off into multiple paths before it hits any component that I could remove.

mlepage
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Re: Re-routing PWR IN on Zero W

Wed Feb 14, 2018 1:49 am

I looked at the Zero W power components with a strong magnifying glass, and compared to the schematic, and a few measurements with multimeter.

If the USB PWR IN jack is down, the 2306KE chip is above it, that's the power chip. It has four capacitors in a line, left to right, which seem to be C8 (1.8V), C4 (5.2V), C3 (5.2V), and C7 (3.3V). Above C3/C7 is giant L1 inductor. Below C8/C4 is smaller L2 inductor. (Why is L1 different on Zero W compared to Zero non-W? Does wireless need more inductance there?) Above C4 is C2, then R1.

That makes sense to me, correct me if I am wrong. (I wish we could host pictures here, I'd post my diagram.)

I'm thinking now, this will be easier than I thought. I was thinking I'd have to desolder the +5V pin on the USB PWR IN jack, because I assumed it would rabbit right into the board. I now see it has a fine trace from the SMD pin to a power plane (basically where the label is PWR IN on the top of the board). So assuming there are indeed no rabbits, I can cut the trace right there!

I'll try this (probably tomorrow) and post my results. But assuming it's just that one trace, this is entirely possible and not too tricky at all. EDIT: Tried it on a spare Zero W. I believe I cut the trace from the PWR IN microusb +5V pin on the top of the board, and also the PP1 on the bottom (three tiny traces). I'm still getting power. Maybe I didn't get it cut enough, or maybe it does route elsewhere in the middle of the wafer. I may have to physically lift the pin.

mlepage
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Re: Re-routing PWR IN on Zero W

Wed Feb 14, 2018 4:13 am

Discovered this similar forum post. Slightly different goal, same idea. No resolution though.

viewtopic.php?t=196599

mlepage
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Re: Re-routing PWR IN on Zero W

Fri Feb 16, 2018 2:25 am

Today I tried ripping off the +5V trace under the pin (on the PWR IN microUSB), and it still has continuity. So I'm pretty sure there's a rabbit right under where the pin is, going into the board. I tried to lift the pin, but the soldering iron doesn't quite get it hot enough. Also it's hard to get in there.

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