After changing the platform for this project to ATMegaxx8 and used an Arduino board to finally debug my code I have started to assemble the prototype version in perfboard. I have decided to go with prudence and wired only the power and crystal lanes so I could check that such "infrastructure" of my board was ok.

Looking at the datasheet the maximum operatinf frequency should be around 15.6MHz for a supply votage of down to 3,0Volts which is close enough to the frequency that the microprocessor should operate.

The first tests running with the CR2025 battery showed that despite there the clock is being generated on the crystal leads, the completely dead.

Tested again with 5.0Volts and the circuit was OK.. This was a bad signal! What have I missed?

After struggling some time with the idea of changing to a larger Tic Tac box or either using a lower frequency crystal I have remembered to check if the Brown Out Detection was active, and which would be its treshold.

The reading of the fuse bits showed that the brown out was set to 2.7Volts, which should not pose a problem as the battery voltage was about 3.0Volts when tested. Nevertheless I have reprogrammed the fuses to disable the brown out detection and this time the circuit started to generate the signals just as expected.