Four-Channel Thermometer on OLED display

This article describes a four-channel thermometer that monitors the temperature at four temperature sensors, and gives a continuous readout on a small 128x32 OLED display:

It could be used in any application where you want to monitor multiple temperatures, such as in controlling a greenhouse, checking the output transistors in a power amplifier, monitoring key points in an overclocked gaming PC, monitoring the chips on a Raspberry Pi, or checking the temperature in different rooms in a home.

Here’s an example of using the Four-Channel Thermometer to monitor the temperature of the power transistors in a Class A power amplifier:

Introduction

The Four-Channel Thermometer uses an ATtiny85 to read the data from four DS18B20 or MAX31820 temperature sensors, using the 1-Wire protocol, and display the temperatures on a small OLED display.

For the display I chose a 128x32 OLED display, a small display about 2.5cm (1”) wide with a very clear, bright monochrome display, and an SPI interface, available from Adafruit [1] or Proto-PIC in the UK [2]. A similar display is also available from Aliexpress [3].

For the sensors I used DS12B20 [4] temperature sensors in a TO-92 transistor package, which have a supply range of 3.0V to 5.5V. The MAX31820 [5] is equivalent and cheaper, but has a maximum supply voltage of 3.7V. Alternatively you can find a pack of 10 DS18B20s on Banggood [6]. The DS18B20 temperature sensors are also available encapsulated into a waterproof cable [7].

You can connect to the temperature sensors using twisted-pair cables of several metres; with long cables a linear topology is recommended rather than a star configuration [8].

The program uses the simple 1-Wire routines from my earlier project, Simple 1-Wire Interface.”

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