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The Pi is plugged into a wall wart and the gert board is connected. I'm having trouble getting the ATMega chip to configure so I can use it and so I started checking some voltages on the board. That's when I found that J7 jumper which is supposed to be 3 volts is more like 3.96 volts? Is this OK?

That's the same voltage I'm finding on the ATMega chip too, so it seems to be under voltage.

The 5V hole on J24 has 4.65 volts on it. Seems like something is not quite right, but the PI is delivering 3.3 volts on Pin 1 and 4.65 volts on Pin 2

Is this normal?


Gertboard manual: http://www.mainelectronics.com/pdf/GERTBOARD_USER_MANUAL.pdf

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  • The 3v3 5v0 should not be more than spec because they are regulated. Possibly the Pi can handle this extra voltage but it might cause issues somewhere else. Check the voltages with nothing plugged into the Pi. My input power is 5.5Volts but after it is regulated it is 5V0, 3V3 as expected.
    – Piotr Kula
    Jul 2 '13 at 12:38
  • Is there a schematic of the gert you can link to? Sep 30 '13 at 7:00
  • @gnibbler, See above, post updated.
    – boatcoder
    Sep 30 '13 at 16:25
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The pi is based on a 3.3v standard most add on kits are 5v you need to add a few bits and bops to help A)boost the power from the pi to the add on or B) power the add on and regulate it to the pi.

Either way I think the issue is the pi power standard is different. The add-on is 5v out right but the 5v pin on the pi may not be able to push that mod and run the pi both at required power.

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  • So, the PI might not be able to push 5 volts, but should the 3.3v part of the gertboard be 4 volts? I would think I'd see a lower voltage on the 3.3v pin, instead of 3.96 volts.
    – boatcoder
    Mar 6 '13 at 20:25
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3.96V is definitely way out of spec for a 3.3V regulator.

I can't see the part number of the (U1) regulator on the schematic. It just calls it REG3v3 and says not to use an LDxxx there.

There are numerous LDO regulator families it could be a member of. Are you able to read the part number off your board? It's possible they somehow managed to put a 4V part instead of a 3v3.

4.65V is very low to be the 5V supply for the pi. You probably need a better power supply. This won't be the cause of the 3.96V on J7 though.

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