Measuring temperatures with TMP03/04 (Part 1)

Part 12345, 6, 7, 8

TMP03/04 is a temperature sensor from Analog Device. Amongst all types of temperature sensors, this one has some very interesting properties: the temperature reading is not based on voltage ouput or impedance changes.

The IC produces a digital signal wich cyclic ratio depends on temperature changes. The on time (T1) is almost stable and nominally 10 ms, while the off time (T2) varies according to the temperature from 15 to 40 ms. The temperature is calculated from the following equation: t = (235 -((T1*400)/T2)), with t in °C et T1 and T2 in ms. I can see multiple advanges from this sensor: no need for analog line and high precision DAC, no need for (very) clean reference power supply. The attenuation in signal which is usually caused by the length of wires between the sensor and the MCU has (almost) no importance. The only thing to care about is the cleaness of the raising and falling edges of the signal. The TMP04 is CMOS/TTL compatible, while the TMP03 has an open collector design which allows sinking higher currents.

For the purpose of testing the sensor on a breadboard, I wired it in this way:

 

Special thanks to Analog for sending free samples.

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