Link Communications RLC-CLUB, User Manual

Page: 174 / 329

12-10
Version 1.73 Copyright © 1997 Link Communications Inc. 1/18/97
If we want to read the battery voltage to the nearest 1/10 volt, we need to detect 10 times as
many levels, 250 and use one decimal place:
102 4 0 0000 0 0250 ; read input 4 on 0.0 to 25.0 volt scale
101 4 1 ; read input 4 with 1 decimal place
Since the divider increases the voltage range that can be read on input 4 by 5 times, it also
reduces the precision to 1/5 of what it is without the divider (from 5mV to 25mV). You can
therefore read your battery voltage with one digit after the decimal point (100mV resolution)
and waste a little resolution, or use two digits after the decimal point (10mV) and exceed the
resolution of the converter. You can put an external voltage divider on input 5 to read external
voltages in a similar way. To use inputs 1..3 with a voltage divider, you would need to
disconnect the built-in pullup resistor.
Let us suppose that we using analog input #5 to to read the voltage supplied by a 3 volt battery
pack with 3 digits after the decimal point (1mV resolution). Remember that the converter has
only 5mV resolution (let us suppose it is exactly 5mV for this example). If the battery voltage
is 3.002 volts, the converter will round it to 3.000. If the voltage is 3.003 volts, the converter
will round it to 3.005. No matter what you do, the last digit read will always be 0 or 5. The
number read back by the controller will sound like it has 1mV resolution, but the reading will
only have 5mV resolution.
If all of this has confused you, ignore it and select 0 digits after the decimal point (or leave it
alone if you haven't changed it - 0 digits is the default).