Thermistor Input; A/D Converter Calibration - Rabbit RabbitCore RCM4200 User Manual

B.4.3.2 Thermistor Input
Analog input LN7_IN on the Prototyping Board was designed specifically for use with a
thermistor at JP25 in conjunction with the
strates how to use the analog input to measure temperature, which will be displayed in the
Dynamic C window. The sample program is targeted specifically for the thermistor
STDIO
included with the Development Kit with R
to use the applicable R
J3
B.4.3.3 A/D Converter Calibration
To get the best results form the A/D converter, it is necessary to calibrate each mode (single-
ended or differential) for each of its gains. It is imperative that you calibrate each of the
A/D converter inputs in the same manner as they are to be used in the application. For
example, if you will be performing floating differential measurements or differential mea-
surements using a common analog ground, then calibrate the A/D converter in the corre-
sponding manner. The calibration must be done with the JP23/JP24 selection jumpers in
the desired position (see Figure B-6). If a calibration is performed and a jumper is subse-
quently moved, the corresponding input(s) must be recalibrated. The calibration table in
software only holds calibration constants based on mode, channel, and gain. Other factors
affecting the calibration must be taken into account by calibrating using the same mode
and gain setup as in the intended use.
Sample programs are available to illustrate how to read and calibrate the various A/D
inputs for the single-ended operating mode.
Mode
Single-Ended, one channel
Single-Ended, all channels
112
THERMISTOR.C
and β values for your thermistor if you use another thermistor.
0
BVREF
LN7_IN
2.2 nF
AGND
JP25
9
Thermistor
Figure B-7. Prototyping Board Thermistor Input
AD_RDVOLT_ALL.C
sample program, which demon-
@ 25°C = 3 kΩ and β 25/85 = 3965. Be sure
0
Inline jumper is
470 W resistor
1 kW
ADC
(RCM4200)
Read
— AD_CAL_CHAN.C
AD_CAL_ALL.C
Calibrate
RabbitCore RCM4200