fakeTec v6 - onboard solar charger

[shimonomihs]

Rev C is currently untested, but should work,

Rev B has a label showing reversed polarity of a capacitor, see comments for more info, other than that, it is reported to be working,

original version is reported to work with hiccups

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After a redesign of the back side of fakeTec v5 I present you fakeTec v6 with added CN3791 MPPT charger for solar panels. This version now features:

• CN3791 MPPT charger
• correct pads for GPS modules
• larger 6x3,6 mm buttons
• solar charger LEDs

I had to also do some compromises:

• only one mosfet for high current switching
• Battery can now be connected only through JST connector
• smaller 0805 components
  There also wasn't space for adding dedicated encoder pads, will make v5 rev B.

Everything else is same as on v5 (if I didn't forget something)

Rev. C changes:

• moved a "+" labes to correct side of a capacitor
  Rev. B changes:
• fixed a via which shorted the XB chip,
• moved components around to accommodate for the JST connector cable.
• changed the 0,5 Ohm resistor package to 2512,
• changed XB label to XB8789D0 and it's resistor to 100 Ohm,
• changed voltage divider resistors to 1 MOhm,
• added pictograms to components to show what they are a part of.

I have not yet tested it, please report any issues.

Parts list:

• 2x 1M 0805 resistors
• 3x 10k 0805 resistors
• 1x 100R 0805 resistor
• 1x 30k 0805 resistor
• 1x 0,5R 2512 resistor
• 1x 120R 0805 resistor
• 5x 0,1uF 0805 capacitor
• 1x 4.7uF 0805 capacitor
• 1x 2,2uF 0805 capacitor
• 1x 47uF 8x10 electrolytic capacitor
• 1x 10uF 106E tantalum capacitor
• 2x 6x3,6 SMD buttons
• 1x SI2312 mosfet
• 2x 1,25 JST connectors
• 1x green 0805 LED
• 1x red 0805 LED
• 2x SS54 schottky diodes
• 1x 100uH SDRH104R inductor
• 1x AO3401A mosfet
• 1x CN3791 MPPT charger
• 1x XB8789D0 BMS
• 1x Nice!Nano V2
• 1x HT-RA62
• 1x 0806 Resistor based on your solar panel voltage:
  6 V - 120k
  9 V - 195k
  12 V - 270k
  18 V - 540k

Design files were made in KiCad 9
licensed under CERN-OHL-P-2.0

(note these images show the rev B version)

fakeTec_V6_revC.zip< View, modify, share

fakeTec_v6_revC_Gerber_files.zip < Send to manufacturer

schematics_V6_revB.pdf < same as rev. B

[Source files](https://github.com/user-attachments/files/21722282/fakeTec_V6_revB.zip) < View, modify, share
[Gerber files](https://github.com/user-attachments/files/21722283/fakeTec_V6_revB_Gerber_files.zip) < Send to manufacturer
[Schematics](https://github.com/user-attachments/files/21722284/schematics_V6_revB.pdf)

Original files:

Design files made in KiCad 9,
licensed under CERN-OHL-P-2.0

fakeTec_V6.zip < view, modify, share

schematics.pdf

[violarulan]

1x 0,5R 4020 resistor

I couldn't find such package on aliexpress. Can you share the link to buy some? ...or is it ok to use 2512 (or some smaller packages) and add some solder on both sides?

[shimonomihs]

I might replace that with something smaller. For the design I referenced the CN3791 board and guesstimated the package size. If you happen to have the board at home, It would be reat to get the package they use.

[valzzu]

I saw this, u should fix this if u wanna use battery 😅
there's no way ur plugging a connector there.

[NomDeTom]

Hey, @ShimonHoranek , this looks like an interesting design. I'm a huge fan of shoehorning stuff into small spaces on circuit boards, and this does a lot in a very small space.

Rather than run your design through a github issue, why not join us on the Meshtastic discord? We can help you out with your design, and you can see the other stuff that people have worked on.

[inakibur]

Hello @ShimonHoranek
I am interested in this PCB to set up nodes with solar panels in my city.
Can gerber be created?
Is the PCB functional?
Greetings and thank you very much.

[valzzu]

@inakibur not sure if anybode has tested this, I have one main concern with this board and its the battery connector.

I saw this, u should fix this if u wanna use battery 😅 there's no way ur plugging a connector there.

[inakibur]

@valzzu For me the battery connector in that position is not a problem, if the connector cannot be connected I put the cable with tin on the plate.

[valzzu]

it does look like it should work without any major issues but there prob is some ripple current and such things cuz there's not that many stitching vias.

[inakibur]

@ShimonHoranek Can't find to buy the XB8089D0, if I change the 1K resistance to a 100OHM resistance, can I use the XB8789D0?
Greetings and thanks!

[lupusworax]

@ShimonHoranek Can't find to buy the XB8089D0, if I change the 1K resistance to a 100OHM resistance, can I use the XB8789D0? Greetings and thanks!

No clue if the listing is available in your country, often having problems sharing links to ali but anyways does this seller shipt to your country?
https://de.aliexpress.com/item/1005005993725347.html

[inakibur]

@ShimonHoranek Can't find to buy the XB8089D0, if I change the 1K resistance to a 100OHM resistance, can I use the XB8789D0? Greetings and thanks!

No clue if the listing is available in your country, often having problems sharing links to ali but anyways does this seller shipt to your country? https://de.aliexpress.com/item/1005005993725347.html

Hello
This seller does send to my country, but I only get the XB8789D0 and in the datasheet he puts that it carries a resistance of 100 ohm in the place of 1k ohm.
Greetings and thanks!

[inakibur]

Good night
Today I mounted the faketec v6. The board lights up well and the battery works.
To test the solar charge I have connected a power supply of 6v 500mha but does not charge the battery, the red LED is turned on but there is no charge in the current measurement in the battery.
I can't find the fault.
Greetings and thanks!

[inakibur]

I have measured the CN3791 test values and they seem correct, tomorrow I will continue to test.
Greetings!

[inakibur]

Good night
Today, by testing, we managed to make it work, the Nicenano and HT RA62 modules work well.
The charge with the solar panel also works, it seems that the CN3791 only works well if you connect a solar panel to it, with tests with the laboratory source not working.
The only problem we have now is that by connecting the lab source to the battery connector, the XB8789D0 chip with 100ohm resistance does not work, I can lower the source to 2 volts and does not turn off.
Greetings and thanks.

[inakibur]

In the two pads marked with an arrow there is continuity with the polymeter and I think there should not be one, am I correct?
Greetings and thanks!

Update:
Following the clues, I managed to correct the failure of the XB8789D0 by piercing the dot marked with a red circle in the photo.

Tomorrow I will upload a video with the faketec v6 working and all the verifications made.
Greetings and thanks.