MA3 Analog Encoder

[chauser]

Our simplest drivebase, where I want to test the systemcore first, use SDS Mark 2 modules with AndyMark MA3 analog encoders as the steering sensors. This is very unlikely to work as is because the MA3 is a 5V device.

However, using a 5V supply for the encoders and a voltage divider on the encoder output seems like it is plausible. To pull that off, I would need to know the input impedance of the SmartIO ports when used for Analog input. The datasheet is uninformative (or at least, confusing) and so my question is: is the 4.7K pulldown resistor enabled in Analog input mode? If not, what is the input impedance in Analog input mode?

[ThadHouse]

I actually was generally testing analog SmartIO with an MA3, and had no issues at 3.3V. Not to say it will work for everyone, but its possible it'll work, especially for testing.

[chauser]

OK! We'll try it. It still would be good to get an answer to the question about the pull-down, though.

[chauser]

We did some more experimentation and measurement with the MA3 encoders. This is just information that may be useful to others -- not a suggestion that anything needs to change.

The 3.3v pin on the SmartIO ports measures 3.304 volts. The maximum voltage on the various analog input pins is about 3.25 volts which reports an angle of 354.5 degrees. It is still unclear to me whether this measurement is only achieved at full rotation (i.e. a full rotation measures linearly from 0-354.5 or whether it goes to 354.5 and then stays stuck there for 5.5 degrees.

So I think that on some mechanisms the MA3s would be usable directly by staying within the range where it is linear and perhaps correcting with a scaling factor. But I'm leary of using them where a full 360 degree range has to be measured -- such as the swerve steering encoders. My recommendation for swerve would be to use the MA3s to set the steering to a known position and calibrate the on-motor-controller encoder to that point.