Question

Design a signal conditioning circuit (SCC) to be interfaced between a MCP9700/9700A and the A/D of a microcontroller. The temperature sensor range to be measured is -5◦ to +30◦C, and the range of the A/D converter is from 0 to 5V.

Answer 1

Answer:

MCP9700 temperature sensor's output follows the equation

Vout = 0.01*Temperature + 0.5 (temperature is in degree centigrade)

(0.01 is the temperature co-efficient of this device)

So at -5 degree, Vout = -0.01*5 + 0.5 =0.45 volt, and

at +30 degree, we have Vout = 0.01*30 + 0.5 = 0.8V

In order to use the full ADC range of 0 to 5V, we need a signal conditioning circuit which can map 0.45V to 0V and 0.8V to 5V. So we do the following:

1. First subtract 0.45 from the sensor output . This gives us a range of 0V to 0.35V

2. Then we amplify the output of subtractor by factor of 5/0.35 = 14.286

This design is shown below.

Hope this helps