TMP37 pin connections.

Arduino TMP37 Centigrade Temperature Sensor Tutorial

by Lewis Loflin

The LCD display used here is NOT an I2C display. This is a direct connection to Arduino.

To use an I2C LCD display see Arduino TMP37 Temperature Sensor I2C Display

Mfr. Part # TMP37FT9Z
Mouser Part # 584-TMP37FT9Z
Cost June 2022: ~$2 QTY. 1

TMP37 is super simple to use with only three connections. It is also fairly accurate despite the 10-bit limitation of the Arduino ADC pin.

Arduino LCD Schematic Typical 2 line by 16 character LCD connection to a generic Arduino module. R1 is used to adjust LCD contrast, pins 15 and 16 are the back light.

In addition a pre-written programming library is available to operate the display to simplify programming.

Here we will learn how to connect a basic Arduino module to a HD44780 based liquid crystal display and use this to display in Fahrenheit the output of an Analog Devices TMP37 temperature sensor.

For better accuracy consider Arduino ADS1115 with TMP37 to Measure Temperature

The ADS1115 is an I2C device that delivers 12-bit accuracy.

TMP37 Specifications and Pin Connections

The TMP37 is intended for applications over the range of 5 degrees C to 100 degrees C and provides an output scale factor of 20 mV per degrees C. The TMP37 provides a 500 mV output at 25 degrees C. Operation extends to 150 degrees C with reduced accuracy for all devices when operating from a 5 V supply.

The low output impedance of the TMP35/TMP36/TMP37 and its linear output and precise calibration simplify interfacing to temperature control circuitry and ADCs. All three devices are intended for single-supply operation from 2.7 V to 5.5 V maximum.

In my test a stable +5 volt supply must be used!

The supply current runs well below 50 uA, providing very low self-heating-less than 0.1 degrees C in still air. In addition, a shutdown function is provided to cut the supply current to less than 0.5 uA.

In this project pin 1 is connected to +5 volts, pin 2 to the analog 0 input on the Arduino module, and pin 3 to ground.

About the Program

An analog to digital converter (ADC) in the ATMEGA168 or ATMEGA328 are 10-bit (1024 steps) and over a range of 5 volts is 5.0/1024 = 4.882 mV per step. The TMP37 produces an output of 20 mV / degrees C. It's easy to see they don't divide equally. Using the original sample program that came with the part when I ordered worked, but was unstable to the extreme bouncing around as much as ten degrees.

So beside rewriting the code to work with a LCD display instead of a computer serial port, I had to deal with the fact we were using very small real numbers and the fact the hardware didn't exactly match. But accuracy came out within a few degrees with a good 5-volt supply.

This produced both a stable reading within 1.5 degrees of a laboratory analog thermometer. (I don't have digital version.)

Download Arduino code tmp37a.txt. Copy-paste to Arduino compiler.

YouTube video for this project: Arduino TMP37 Centigrade Temperature Sensor Tutorial

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