Add operator to convert raw adc units to volt #24
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Interface/Harp.Behavior/AdcToVolt.cs
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| // ADC input = 2.0 V means 5.0 V on boards input | ||
| // 4096 -> 3.3/1.6 = 2.0625 V | ||
| // ~3972 -> 2.0 V @ ADC -> 5.0 V @ Analog input | ||
| return (float)(5.0 / 3972.0) * adcValue; |
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1 - To be more precise, the 2.0625V is the configured maximum range of the Atxmega ADC, however the maximum value that the ADC receives when the input is at 5V is dependent on input resistive divider, i.e. 15/39 * 5V for hw >=v2.0. Therefore Vmax input ADC = 1.92307V ~ 3918.2 => return (float)(5.0 / 3918.2) * adcValue;
2 - For hw <= v2.0 the value is 16/40*5V = 2V ~ 3970.9;
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ok this is not good... @glopesdev I can only think of having an extra property that sets this value and it is by default for hw>=2.0. From the point of view of the interface, there is no way to distinguish a message coming from different hw versions, unfortunately.
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Ok after thinking about this. I think we have 2 options
- Have two options in the operator that can be toggled for the two converters
- Change the firmware in <hw 2.0 boards to correct the raw adc unit scale to the same scale as hw2.0. From the point of view of the interface they would be fully compatible.
I am leaning towards the second solution has it would make the system a bit more robust from the point of view of the user. So I think for now we just implement this operator for hw 2.0 and release a new firmware version with the full scale patched.
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@bruno-f-cruz @artursilva0 @filcarv there is a 3rd option to consider: generate two different packages, one for Behavior v1 and one for Behavior v2.
It might make sense because there are other differences than just the scaling factor, for example the v1 only has one ADC, so the packages could be structurally different.
We could either keep them in the same repo and have two branches with different YML files, or two different repos.
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This PR adds an operator that can be used to convert a raw adc payload to a struct wit converted SI volt units. The current implementation allows bare payloads or Timestamped.
It should be noted that if in the future we add converters support to the device.yml, one can make this operator backward compatible by simply making it a passthrough on top of the converted values.