Quote:
Originally Posted by Cal578
The analog module is a single-side measuring circuit, reference to ground. You would need a translation circuit in between to make the measurement work safely.
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This is not entirely true, while the analog module range is limited to 10V, it is limited to 10V in both positive and negative directions. That is to say they're good for +/- 10V. Now, you'd still need to divide the voltage down (this is how the system measures the battery voltage) to make it compatible. For a good example of how to do this, reference the analog breakout schematic here:
http://www.usfirst.org/uploadedFiles...matic%20v3.pdf
Page 2 of that PDF, upper right corner shows the voltage divider used to measure the battery voltage, which is a 680 ohm and 1k ohm resistor. These values allow about a +/- 16.8V maximum input. This is more than sufficient for your purposes.
As far as the PWM problem goes, the simplest solution is a low pass filter with a tight corner frequency, that is sufficiently above the bandwidth you'll need for your control application, while being as far under the PWM frequency of the Jaguar as possible. This will result in an average voltage at your input proportional to the duty cycle of the PWM output by the Jaguar. Supposedly, the Analog Breakout has a 1600Hz single pole filter on each input, which should be quite sufficient (if memory serves, the Jags switch in several 100s of kHz region) but I can't confirm that.
Page 3 of this document:
http://www.usfirst.org/sites/default...20Breakout.pdf references a 1600Hz per channel filter, but I do not see it on the above linked schematic, so I am a bit confused on that.
Either way, adding your own 1600Hz or so filter to the signal is easy with a few basic components and some perfboard, and will only assist any existing internal filter, giving you the information you are seeking.
That said, I couldn't tell you a thing about it's legality, and I wonder about its effectiveness compared to more traditional tachometry approaches. It is a fun and interesting design challenge though!
Matt