Magnetic Encoder Wiring and Programming

[Gabriel Mendes]

Hi Everyone, does someone knows how to wire the Magnetic encoder in the Sidecar or in the roboRIO and does someone knows how to program a magnetic encoder in labview?
The Magnetic Encoder number is AS5145B, Eval Kit.
Thanks, Go #1382

[TFleig78]

Last year, we used this sensor and it worked reliably. To wire it, we used a low pass filter to average the PWM signal. There are instructions to build the filter on page 18 of the datasheet here:

http://ams.com/eng/Products/Position...ensors/AS5145B

Do note that when used in this way, the sensor outputs a value proportional to it's absolute position, so it can be used like a potentiometer. For us this was perfect as we were not counting number of rotations, but rather what angle the shaft was within a rotation.

The pinouts are on page 4. +5v is pin 16, and Gnd is pin 7. We wired these to the digital sidecar last year, but I think you can wire them right to the DIO on the RoboRio.

[Ether]

Originally Posted by TFleig78

we used a low pass filter to average the PWM signal

Or you can use the FPGA to measure the pulse width? WPILib counter object semi-period mode.

http://www.chiefdelphi.com/forums/sh...32&postcount=5

[TFleig78]

You can also use it like a normal ecoder with A and B channels.
This article is very helpful:

http://wpilib.screenstepslive.com/s/...control-system

[Joe Ross]

Originally Posted by Ether

Or you can use the FPGA to measure the pulse width? WPILib counter object semi-period mode.

http://www.chiefdelphi.com/forums/sh...32&postcount=5

Semi-period mode is not ideal for this sensor, because the data sheet recommends using the duty cycle. When there is motion, you could get out of sync values if you're trying to measure the duty cycle in semi-period mode. You could measure just the high or low pulse and use other methods to calibrate out the 5% frequency tolerance.

[Ether]

Originally Posted by Joe Ross

Semi-period mode is not ideal for this sensor, because the data sheet recommends using the duty cycle.

Good catch (paragraph 8.2 of the AS5145B datasheet).


The same holds true for the US Digital MA3:

Originally Posted by Ether

Decoding PWM duty cycle (which is the datasheet-recommended way to decode the PWM signal for the MA3) would require measuring both the pulse width and the period (or the associated non-pulse width) for the same cycle. I don't think the 2014 FPGA is programmed to do that.

Originally Posted by Ether

I've heard the FPGA sampling frequency will be bumped up from ~153KHz (in 2014) to ~1MHz (in 2015). Maybe the FPGA will be programmed in 2015 to read duty cycle (detect and report consecutive rising-to-falling and falling-to-rising edge pairs). If so, you could decode the PWM quite accurately using that.

Do you know if there are any plans to add duty cycle decoding to FPGA?