RoboteQ AX2550/2850 Selecting the Potentiometer Value, = U/R = 5V / 1000 Ohms = 0.005A = 5mA

Analog Control and Operation

+5V	14
		AX2500 Internal Resistors
Analog	10	and Converter
		47kOhm
Input 1 or 2
	11		A/D
10kOhm		10kOhm
		47kOhm
	13
Ground

FIGURE 64. Potentiometer connection wiring diagram

The controller includes two 47K ohm resistors pulling the input to a mid-voltage point of 2.5V. When configured in the Analog Input mode, this will cause the motors to be at the Off state if the controller is powered with nothing connected to its analog inputs.

Important Notice

The controller will not activate and will display the “no ctrl” message after power up or reset until the analog inputs are at 2.5V

FIGURE 65. “no control” message indicates that joystick is not centered at power up

Selecting the Potentiometer Value

The potentiometer can be of almost any value; however, undesirable effects occur if the value is too low or too high.

If the value is low, an unnecessarily high and potentially damaging current will flow through the potentiometer. The amount of current is computed as the voltage divided by the poten- tiometer’s resistance at its two extremes. For a 1K potentiometer, the current is:

I = U/R = 5V / 1000 Ohms = 0.005A = 5mA

For all practical purposes, a 1K potentiometer is a good minimal value.

If the value of the potentiometer is high, then the two 47K resistors built into the controller will distort the reading. The effect is minimal on a 10K potentiometer but is significant on a

110 AX2500/2850 Motor Controller User’s Manual Version 1.7. February 1, 2005