Won't save to SD without Serial Connection

The existing topic under this header has not been posted to for 120 days so I'm starting another.

My 6-sensor beehive temperature monitor illustrated at www.dheaf.plus.com/monitor/ will save data to the SD with FTDI (3.3V) USB adapter connection to my PC, but not with the 18650 cell in the monitor. That cell is connected to a 3.3V voltage regulator on the on/off switch board.

All VCC terminals show a fraction over 3.4V with the FTDI, but 3.3V with the battery/regulator. All wires are tested for continuity. Anyway, the fact that the SD records with the FTDI indicates that the circuits are intact.

The above link lists all the boards etc.

Any suggestions welcomed.

A complete circuit diagram (not fritzing) is required otherwise all we can do is guess.

Pete

el_supremo:
A complete circuit diagram (not fritzing) is required otherwise all we can do is guess.

Thanks for reading this. I have added one (of sorts) to 6-sensor temperature monitor in a Warré hive .

I should add that the whole monitor works with just the VCC and GND wires from the FTDI serial adapter connected to the Arduino, i.e. saves a file to the SD.

Another test: without the FTDI connected, I supplied 4.2V from a 18650 cell to RAW on the Arduino, with the negative of the cell to the GND bus/net. The VCC of all boards showed 3.25V (due to the regulator in the Arduino), but no files are saved to the SD card.