This article describes a four-channel thermometer that monitors the temperature at four temperature sensors, and gives a continuous readout on a small 128×32 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:
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 128×32 OLED display, a small display about 2.5cm (1″) wide with a very clear, bright monochrome display, and an SPI interface, available from Adafruit  or Proto-PIC in the UK . A similar display is also available from Aliexpress .
For the sensors I used DS12B20  temperature sensors in a TO-92 transistor package, which have a supply range of 3.0V to 5.5V. The MAX31820  is equivalent and cheaper, but has a maximum supply voltage of 3.7V. Alternatively you can find a pack of 10 DS18B20s on Banggood . The DS18B20 temperature sensors are also available encapsulated into a waterproof cable .
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 .
For more detail: Tiny LED Time Watch