Digi RCM4000 - Manual (Page 108)

102 RabbitCore RCM4000
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
THERMISTOR.C sample program, which demon-
strates how to use the analog input to measure temperature, which will be displayed in the
Dynamic C
STDIO window. The sample program is targeted specifically for the thermistor
included with the Development Kit with R
0
@ 25°C = 3 k
Ω and β 25/85 = 3965. Be sure
to use the applicable R
0
and
β values for your thermistor if you use another thermistor.
Figure B-7. Prototyping Board Thermistor Input
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 not yet available to illustrate how to read and calibrate the various
A/D inputs for the three operating modes.
Mode Read Calibrate
Single-Ended, one channel — AD_CAL_CHAN.C
Single-Ended, all channels AD_RDVOLT_ALL.C AD_CAL_ALL.C
Differential, analog ground AD_RDDIFF_CH.C AD_CALDIFF_CH.C
9
1 kW
LN7_IN
BVREF
Thermistor
JP25
J3
2.2 nF
AGND
ADC
(RCM4100)
Inline jumper is
10 kW resistor