RoboteQ AX2850 user manual Using the Analog Inputs to Monitor External Voltages

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.

To Battery +Terminal

47kOhm

4.7kOhm

+5V 14

Ana 1: 11

Ana 2: 10

Ana 3: 12

Ana 4: 8

Ground 5

Internal Resistors and Converter

47kOhm

A/D 10kOhm

47kOhm

FIGURE 37. Battery voltage monitoring circuit

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.

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