Book Analog Interfacing to Embedded Microprocessors
65v. We can make a chart showing the actual
ADC result for each temperature in the range:
Temp °C Rth Opamp ADC result
Output (Decimal)
10 18.2K 4.44v 227
25 10K 2.18v 111
30 8.276K 1.44v 74
40 6.406K .467v 23
You need the chart because the thermistor isn’t linear, so the software
needs to know what ADC value to expect for a given temperature. If this were
a real application, we would probably calculate the chart in 1-degree incre-
ments. For this specific example, the opamp has to swing almost all the way
between 5v and ground, so it either needs to operate from positive and neg-
ative voltages, or else a single-supply, 5v-only opamp with rail-to-rail output
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