IvCurve Improvements

[orgua]

There are some flaws in the current recording of ivcurves:

1. resetting voltage-ramp has side-effects and takes a specific ammount of time, depending on the light-intensity of the solar cell
   • there should be a parameter (blind gap) to avoid recording in this window - the previous value should be hold
   • this can be also done dynamically for when 2 consecutive voltage-readings are 99% equal
2. (see plot below) VOC of BQ is higher than shepherds VOC, mostly because shepherd triggers for when a current is detected, but below a certain threshold. looking at records the voltage can plateau at 2.1 for a while (real VOC), the slowly ramp down to 2.0 V and first current is recorderd at around 1.99 V, so VOC for shepherd is ~ 5 % lower than it should be
   • to solve this shepherd should use the highest recorded voltage OR at least make it configurable
3. while moving down the voltage ramp - the recorder leaves the plateau and the current spikes
   • this is visible in the plot below and could be an effect of the solar cell
   • but is more likely some transient ringing in the gain-circuit
   • it is only visible on higher light-intensities though