Quote:
Originally Posted by Trump
6) Not really about CAN, but does anyone know if the potentiometers must be 10k, as per the jaguar manual, or is it possible to use other values?
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In short, It would be easiest to use a 10K pot.
You can use other values, but let's look at the schematic first (page 24 of the
RDK-BDC24 User's Manual).
Notice there is a 1K resistor in series with the '+' pin on the Potentiometer input header J3. When a 10K pot is wired to this header as per the datasheet, the resistor and pot act as a voltage divider. This puts 3.0V across the pot (3.0V = [10K/(1K + 10K)]*3.3V) making 3V the maximum voltage the wiper can be. This is perfect because the ADC (Analog to Digital Converter) pins on the Jaguar's microcontroller can only read 0 - 3.0V.
The ADC on Jaguar is a 10-bit ADC, so it measures 0 - 3.0V in 1024 discrete steps. So if you were to use a lower resistance pot, let's say 5K, your wiper will swing between 0 and 2.75V (2.75V = [5K/(1K+5K)]*3.3V). This is well within the range of the ADC, but you are only measuring the full range of the pot with approximately 940 steps rather than 1024.
Let's say you go with a higher resistance pot, 20K, your wiper will swing between 0 and 3.14V. The ADC can still only measure up to 3.0V, so the last 0.14V will just cap the measurement at 3.0V. Let's say that you have a 10-turn pot; the last 0.14V can be equal to 160 degrees of undetected motion!
So in conclusion:
Yes, you can use different values of potentiometers, but be aware of how the different values can affect your system.
TI recommends using a 10K pot for simplicity and maximum resolution over the maximum range of the pot.
-David