Digi BL1800 user manual Void anaOutint channel, int value

Table 5. Typical Analog Output Voltages Corresponding

to Values in anaOut Function

Channel	0	PWM_MIN	PWM_MAX	1024
DA0	0.08 V	0.08 V	2.875 V	3.4 V
DA1	0.004 V	0.63 V	3.6 V	3.6 V

The output value is set using the following function.

void anaOut(int channel, int value);

sets the state of an analog output channel. jrioInit must be called first.

channel is the output channel number (0 or 1 on the Jackrabbit).

value is an integer from 0–1024 that corresponds to an output voltage as shown in Table 5.

NOTE: See the sample program JRIOTEST.C for examples of using the anaOut func- tion.

Effect of Interrupts on Analog I/O

The stability of the voltage output (and hence the voltage input determination as well) depends on the ability of the driver to respond quickly to interrupt requests. Dynamic C debugging, use of the printf function, or any serial communications can disrupt the pulse-width modulation utilized by the driver and cause fluctuations in the voltage out- puts. Avoid using serial communications or printf statements during portions of your program where the voltage must remain steady. Also be aware that debugging and running Dynamic C in polling mode will cause fluctuations. Finally, be certain to disable the PWM drivers by setting the output values to 0 or 1024 when you are done using them to free up the CPU.

Calibration of Values to Voltages

The analog output channels on the Jackrabbit can be more accurately calibrated for each individual Jackrabbit in the following manner (calibration of DA0 is assumed in this example, calibration of DA1 would proceed similarly):

•Set desired channel output to PWM_MIN.

•Measure voltage Vmin on DA0.

•Set desired channel output to PWM_MAX0.

•Measure voltage Vmax on DA0.

A linear relation between input value and voltage can now be calculated:

b = Vmax – m ⋅ PWM_MAX0

User’s Manual 53