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Originally Posted by Don Rotolo
NEVERTHELESS. If IFI states so clearly "Always use 100k pots", who am I to argue??
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Since there seems to be some confusion on this subject.. the reason IFI requires 100K ohm pots is because of the design of the analog input of the OI. Between the analog input pin on the OI and the actual connection to the microcontroller inside there is a pull-down resistor. This is also why you are not supposed to connect the other side of a potentiometer connected to the OI to ground (see OI reference guide page 5). The pull-down resistor creates a voltage divider with the potentiometer, such that even when the pot is turned all the way down the processor inside will still see some voltage. The effect of this is that the only way the OI will see 0v at the analog input is when nothing is connected to it.
The whole point of this setup is a safety mechanism. With this configuration, the OI knows if there is nothing connected to an analog input (because it will read 0v). Using the software inside the OI, they can remap a 0v input to send the value 127 to the robot. Bottom line: if you have a joystick plugged in to your OI and you're using it to control your robot, and someone accidentally yanks out the joystick cord, do you want your robot to see 0 or 127? If your robot saw 0, it would suddenly go full reverse if the joystick was unplugged!
Now, the reason it has to be 100K ohm is because of the value of the pull-down resistor. If you use something less than 100K, you will be changing the minimum voltage that you can send into the OI which will limit the range of values that your robot will see in response to moving the pot.