Implementation of the optimised gain settings

[JochiSt]

In #18 a optimised gain setting has been found, which needs to be implemented in hardware (exchange of resistors) and software (configuration values).

The results from #18 are: U channel:

• R1 = 330k
• R2 = 56k

I channel:

• R1 = 470k
• R2 = 56k

[JochiSt]

TODOs:

Software / Firmware:

• [x] write configuration into EEPROM
• [x] test variable gain setting

PCB changes: (only population)

• [x] current source 1
  • [x] R1 / R2 U
  • [x] R1 / R2 I
• [x] current source 2
  • [x] R1 / R2 U
  • [x] R1 / R2 I

[JochiSt]

There is a problem with reading back the gain settings see #21.

This problem has been solved.

[JochiSt]

I've implemented sending out the measured and calculated temperatures.

These are the values, the PID is working on. It seems, that this needs a bit of tuning to get the best results. Especially in the region, where two different gain settings are used, the behavior can be better.

A current calibration in order to determine the real gain of the amplifier seems a good next step.

[JochiSt]

The pink curve is the internal used temperature, the wiggles at about 100s might be a problem for the PID controller.

[JochiSt]

The gain setting resistors listed in https://github.com/JochiSt/OpenFlowMeter/issues/20#issue-1516488905 are by a factor of 10 to large.

Those values cause might cause the amplifier to cause strange effects in the unity gain setting. (see https://github.com/JochiSt/OpenFlowMeter/issues/22#issue-1518569229)

This problematic was solved in https://github.com/JochiSt/OpenFlowMeter/issues/22#issuecomment-1371897907.

The correct gain setting resistors are (Ch0):

• R47 = 47k
• R51 = 5k6
• R46 = 33k
• R50 = 5k6

And same for Ch 1.

[JochiSt]

From the HG to the LG of the current section, there is some slight mismatch, which causes the temperature to be negative. (Means, that a too high current is measured)

[JochiSt]

The gain switching is working. Although it needs some improvements. (There is always room to improve things)