Celsius converter to digital code from remote sensor

This circuit is originally published by Elana Lian and Chan Tran (Analog Devices). This simple single supply system enables to measure remote temperature with less than 1°C error in a range of 0 to 100°C:

The circuit consists of the following parts: T1- low-cost AD590 temperature sensor; AD8541 – rail to rail amplifier; four resistors; potentiometer; and ADC AD7416. Use precision resistor RF for amplifier feedback to minimize scale factor.

AD590 sensor provides output current proportional to absolute temperature(1uA/K). So with rail to rail of 0 to 5V scale factor is 50mV/°C. AD8541 is low cost and a low-power operational amplifier. It has a convenient voltage range of 0 to 5V and a low bias current. The amplifier’s output swing is 25 mV to 4.965V with a single 5V power supply, limiting the output by about 0.5°C on both ends.

The output AD590 varies from 273.15 to 373.15uA for a temperature range of 0 to 100°C.

To achieve an accuracy of 1°C – the circuit needs to be calibrated by adjusting the trimming potentiometer. Just adjust the trimming potentiometer so that at 25°C, the amplifier output would be 1.250V or desired code at ADC. Because the sensor has a current output, it is immune to voltage-noise pickup and voltage drops in the signal leads; you can thus use it at a remote location. Use a twisted-pair or shielded cable to minimize noise. Celsius converter to digital with remote sensing can be successfully used in home automation projects, car, weather monitoring.

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