Testing Board Features
2016 Microchip Technology Inc.
DS50002480A-page 29
3.3.5
Read ADC Tab
The MCP3221 Analog-to-Digital Converter uses both a fixed 2.5V voltage reference
and the power supply from an MCP1525 voltage reference chip, which allows the
conversion to be independent of the demo board’s power line: 3.3V/5V.
Therefore, the analog voltage to be measured must be between 0 and 2.5V. The board
can be used to measure the voltage from:
• Potentiometer R13, from the 2.5V supply that’s also powering the MCP3221 if
jumper J18 is connected (the default setting);
or
• An external source (via J7 and J8) if jumper J18 is disconnected.
In case of continuous monitoring, samples are taken once per 100 milliseconds, so
higher frequency variations may not be noticed by the PC application.
The software provides the option not to display specific variations (such as populating
the ADC graph) to reduce the amount of tasks that the PC must perform. This is
especially useful when the PC is running low on system resources (such as processor
usage or memory filling). Even when switching to a different application tab, if the
monitoring is enabled, then it will not be automatically halted unless the board is
physically disconnected from the PC. Therefore, it is recommended to stop performing
the measurements when they are no longer required. Prior to performing measure-
ments, make sure to select the analog voltage source by connecting or removing
jumper J18. See
Table 2-1
for more information.
3.3.5.1
TAB OPERATION
Select the
Read
ADC
tab to perform ADC measurements.
The “Show in Chart” check box determines whether a chart is generated by the system
to illustrate the measured values.
The functionalities of the “Show numbers” and the “Log into .CSV File...” check boxes
are similar to the ones described in
Section 3.3.2 “Measure USB Power Tab”
.
However, the
.csv
file contains two columns and each set of readings is placed on a
row. The columns are: Data entry index, Voltage (in Volts).
The functionalities of the S
tart Measurement, Stop Measurement
and
Reset
Measurement
buttons are similar to the ones described in
Section 3.3.2 “Measure
USB Power Tab”
.
The
Measure ADC Voltage Once
button is for the application to retrieve, in real time,
just one set of numeric values (for voltage) and to write them inside the text box below
it. This can be used as an alternate solution to
Start Measurement
in order to save
system resources.
Custom LED notifications (for example: voltage readings above 2.31V results in a green
LED blinking on the board) are described in
Section 3.3.8 “RGB LED Notifications Tab”
.
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