13.8 * 10100 / (10100 + 32670)
= 13.8 * 10100 / 42770
= 3.25883V
The tolerance of the voltage regulator’s output is ±0.25V, and thus the lowest count from the
A-D convertor will occur for the lowest input voltage and the highest reference voltage, and
would be a count of: 2465. The highest count would be for the highest input voltage and the
lowest reference voltage, and this would be: 2810.
From this the calibration factor limits can be calculated. The nominal count would of course
still be 2629.
The calibration factor required therefore is:
13,800,000 / 2629
= 5249
and thus the calculation would be:
display
V
= (ADC * 5249) / 10,000,000
Inserting typical values:
Raw O/P = 2629 * 5249
= 13,799,621
Now, however, if the calibration factor is changed by 1 increment, the display would be:
Raw O/P = 2629 * 5250
= 13,802,250
This gives an increment of 2.6mV/ step, and thus allows the voltage to be more accurately
approximated, as it is using the optimum step size of ±1/2LSB.
Whilst in practice temperature variations are likely to cause errors which exceed this,
nevertheless a worthwhile improvement in accuracy has been achieved at no extra cost other
than an alternative algorithm.
Current Measurement
The ammeter in the TRX2 only measures the drain current of the output amplifier, not the
total current consumed by the transceiver. Nevertheless, in order to accurately set the bias
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