Those of you who are following this Project will know from my last log that I have been plagued by intermittent resets whilst loading firmware and testing the pcb. I have at last managed to trace the cause and capture the offending waveforms on my digital 'scope. The design uses an LDO to provide the 3.3V required by the ESP8266. The particular LDO used TPS77733 monitors the regulated voltage and provides a signal should it drop by 5% . This signal can be used either as a 'power low' or as a Reset'. Unfortunately I chose the latter. Consequently whenever the ESP8266 draws heavily on the regulated supply, for for example during wireless setup or firmware loading, then the PCB resets.

The screen capture above shows the 3.3V (red trace) and the reset line (blue trace). The Input Voltage tothe LDO (Vcc) comes from the GPIO pins of a Raspberry Pi, Nonimally 6V at 600 mA but obviously inadequate. I now await delivery of a stabilised Laboratory PSU to continue testing. Hopefully these problems won't recur when powering from the a solar panel with a fully charged backup battery.