RoboteQ AX2850 - Manual (Page 67)

AX2550 Motor Controller User’s Manual 67
Using the Analog Inputs to Monitor External Voltages
To read the temperature, use the ?p command to have the controller return the A/D con-
verter’s value. The value is a signed 8-bit hexadecimal value. Use the chart data to convert
the raw reading into a temperature value.
Using the Analog Inputs to Monitor External Voltages
The analog inputs may also be used to monitor the battery level or any other DC voltage. In
this mode, the controller does not use the voltage information but merely makes it avail-
able to the host microcomputer via the RS232 port. The recommended schematic is
shown in Figure 37.
Using these resistor values, it is possible to measure a voltage ranging from -5V to +60V
with a 0.25V resolution. The formula for converting the A/D reading into a voltage value is
as follows.
Measured volts = ((controller reading + 128) * 0.255) -5
Note: The A/D converter’s reading is returned by the ?p command and is a signed 8-bit
hexadecimal value. You must add 128 to bring its range from -127/+127 to 0/255.
Connecting User Devices to Analog Inputs
The two analog inputs can be used for any other purpose. The equivalent circuit for each
input is shown in Figure 38. The converter operates with an 8-bit resolution, reporting a
value of 0 at 0V and 255 at +5V. Care should be taken that the input voltage is always posi-
tive and does not exceed 5V. The converter’s intrinsic diodes will clip any negative voltage
or voltage above 5V, thus providing limited protection. The value of the analog inputs can
be read through the controller’s RS232 port.
47kOhm
10kOhm
47kOhm
47kOhm
4.7kOhm
Internal Resistors
and Converter
To Battery
+ Terminal
+5V 14
Ground 5
A/D
Ana 1: 11
Ana 2: 10
Ana 3: 12
Ana 4: 8
FIGURE 37. Battery voltage monitoring circuit