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Celsius converter to digital code from remote sensor

2014-11-14 07:12  
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This circuit is originally published by Elana Lian and Chan Tran (Analog Devices). This simple single supply system which enables to measure remote temperature with less than 1?°C error in a range of 0 to 100?°C:

celcius converter

Circuit consists of following parts: T1 a€“ low cost AD590 temperature sensor; AD8541 a€“ rail to rail amplifier; four resistors; potentiometer; and ADC AD7416. Use precision resistor RFfor 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 low-power operational amplifier. It has convenient voltage range of 0 to 5V and low bias current. The output swing of the amplifier is 25 mV to 4.965V with a single 5V power supply, limiting the output by about 0.5?°C on both end.

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

In order to achieve accuracy of 1?°C a€“ circuit needs to be calibrated by adjusting trimming potentiometer. Just adjust 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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