Boost voltage

[Claudio L.]

(06-04-2015 03:46 PM)Tugdual Wrote:  Remaining question is what is the actual minimum voltage @ which the 50g can safely operate.

I tested this last year. I don't remember exact values, but roughly these were the ballpark numbers:
The calculator idles in a "slow" clock, and jumps to a faster clock on demand.
I think for aklalines (nominal 6V) it was around 4.4V was still "safe", because when the turbo mode kicked in, the voltage dropped to about 3.8V and was still OK.
For rechargeables (nominal 4.8V), 4.0V was "safe", with voltage dropping to 3.5V or so on demand.
When voltage was around 3.3V the CPU would reset randomly.
But this is for bare minimum hardware. I didn't test if for example writing to flash could be achieved with only 4.0V, as it may drain more current. Also I didn't test if an SD card could function properly (voltage wise probably OK since they switch to their own voltages anyway, but current wise... may read OK but not write for example).

That the CPU can function doesn't mean is 100% safe, as I didn't test a worst-case scenario by any means.

I measured this using newRPL firmware, which has "slow" mode at 6 MHz and with the CPU in IDLE mode (Wait for interrupt), so it's supposed to drain less current than the stock firmware (12MHz with the CPU fully awake). On the other hand, the "fast" mode is 192 MHz (vs. 75 MHz stock), that's why the voltage drops are so steep.