EmonTH - no power

My EmonTH (v1.4) was working for a few months after I got it last year and eventually it stopped and I forgot about it. However, looking at it again it seems like it's not the batteries but rather something else that's the problem. With a fresh set of alkaline batteries I can read 3.3V across the battery terminal but only 2.5V between the 3.3V and GND rails at the 6-pin header.

The unit works as normal when I plug in the UART USB programmer, but obviously that's not ideal for a remote sensor.

Any ideas what to check?

pb66's picture

Re: EmonTH - no power

You must be reading a voltage through the reset pullup or the voltage reg as there isn't a 3.3v at the 6pin header.

What voltages to you see at the unpopulated 2x3pin ICSP header (pins 2 & 6)  ?


Robert Wall's picture

Re: EmonTH - no power

Or you should see 3.3 V between 2 & 3 of the 6-pin terminal block (if fitted, otherwise its pads on the edge of the board).

seannation's picture

Re: EmonTH - no power

@pb66, sorry, I meant the 6-pin terminal block as Robert mentioned, not the UART header. I read ~2.5 V across pins 2 and 3 of the terminal block. I also read ~2.5 V between pins 1 and 3, where pin 1 is "5V/BATT", so I assume the problem is in the circuitry between pin 1 and the battery +V rail?

Thanks for your comments so far.

Robert Wall's picture

Re: EmonTH - no power

Pin 1 is indeed the 5 V incoming supply, but it isn't the battery terminal. What you appear to be seeing there is a reverse feed through the XC6206 3.3 V regulator.

The 3.3 V rail comes from the battery via a LTC3525 step-up converter, so it looks as if that or its supporting components are the prime suspects.

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