13 Jun
2009
13 Jun
'09
4:18 a.m.
On Fri, 2009-06-12 at 21:31 -0400, Bill Sudbrink wrote:
Eric Smith wrote:
Close enough, for this. It's just a potential divider. Have you tried
it?
Wired like that, the exact value of the
potentiometers doesn't matter.
If it's easier to find joysticks with 10K potentiometers, they should
work. Too low a resistance will draw too much current (possibly
exceeding current or power ratings of the potentiometer), and too high a
resistance (relative to input impedance of the ADC) things won't work
properly, though no damage will result.
Well, PC and Apple joysticks (easy to find) are between 100k
and 150k Ohms... 20 to 30 times the desired values. Some RC transmitters may have 10k pots. My only knowledge of
RC
transmitter pot values is a couple of web pages about retro-
fitting a board with a PIC on it into old analog transmitters
to get digital control of the model. The pages say things
like "If you have 5k pots, install this resistor and cap.
If you have 10k pots, install this other resistor and cap."
etc..
That's because it uses the RC time constant to measure the value of the
pot. It doesn't care about the voltage. You set the pin to output low
so you discharge the cap and then set it to be an input and time how
long it takes to go high again. The higher the pot value, the longer
the time.
Gordon