Manual 104-AIO16A and 104-AIO16E
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Many devices using digital potentiometers require the software to load the calibration coefficients from a
file-on-disk, matching the file to the board based on a manually entered serial number, or some similarly
complex method. This board instead contains EEPROM to store the calibration constants. This makes it
very simple: the board remembers its own constants, there’s no need for a file on disk, or serial number
lookup databases, etc.
The details are different between A/D and DAC calibration, and are discussed separately, below.
Breakdown: Calibrating the DACs
DAC calibration is very simple, and provides a clear introduction to several of the concepts used in
calibrating the A/D. The process is designed to evaluate the differences between what you’ve asked the
DAC to output and what it really produces. This difference is the amount the board is out of calibration. By
adjusting digital potentiometers in the DAC circuit, you reduce this calibration error by successive
approximation until it reaches zero. When it is zero, and the board is calibrated, you store the amount of
adjustment for later use.
First, let’s expand Step 1 mentioned above into its component sub-steps for the DAC:
Step 1.
Determine the Calibration Constants for the DAC
1.1
Output a value corresponding to a known voltage
1
on a DAC
1.2
Measure the output value of the DAC with a DVM
1.3
Adjust the value in the digital calibration potentiometer for that DAC until the voltage read
by the DVM matches the known value being output.
1.4
Store the value from the digital calibration potentiometer into a spot
2
in the EEPROM for
use on the next and subsequent board initializations.
1.5
Repeat steps for the other DAC.
Step 2.
Write the Calibration Constants into the Calibration Potentiometers
For details on Step 2, please refer to section “Step 2" near the end of this appendix.
1
: The value corresponding to a known voltage to output depends on the range of the DAC as selected by
jumpers on the board. Software can determine the current jumper configured range using the status
register at Base + 8 (Chapter 6).
2
: The correct spot in EEPROM varies with the DAC number being calibrated, and the currently selected
range (see note 1). Please note, you could use any location in the EEPROM you want, as long as you
always use the same location. We recommend you use the same locations as our provided Calibration
program, drivers, and samples, as shown in
Table B-1
, following.
