2 thermometers based on PIC12F629 . Included C code and circuit diagram. Displays -55 to 125 °C.
The temperature is read every 2 seconds. Sensors are DS18B20. 4 digits are used for each thermometer.
LED brightness can be set in the code, value can be 0-15.
It can be used for temperature inside and outside the house.
The 7 segment LED is a module of 8 digits driven by MAX7219, I got it from eBay.
When programming the PIC disconnect the sensors from pins 6 and 7.

You are free to use the circuit diagram and the software with no limitations.

The temperature is read every second. Sensors DHT11. 3 left digits are used for temperature 2 digits on the right are humidity.
LED brightness can be set in the code, value can be 0-15. MAX7219 is driven by software SPI. DHT11 reply with 5 bytes of data 3 are used to display temperature and humidity.
The sketch and circuit can be used without any changes for ATtiny13/25/45/85
ATtiny13 can be programmed using Arduino IDE and Arduino as ISP. Use these instructions https://www.electronics-lab.com/project/how-to-program-attiny13attiny13a-using-arduino-ide/ with the setting : 9.6MHz, no millis no tone, LTO enabled.
ATtiny can be programmed using Arduino IDE and Arduino as ISP, see Technical Tips Burning bootloader with setting "Clock Source 8MHz internal", "LTO enabled".

Nano ATtiny88 board and thermocouple module with MAX6675. Displays 0 to 1023 °C . 10K potentiometer set the temperature, when SET pushbutton pressed the set temperature is displayed. The relay output can drive a relay or a Solid State relay. Hysteresis is +/- 5 degrees.
The project can be used as a thermometer by removing the bushbutton and the pot.
The temperature is read every 1 second, can be changed in the code.
The 7 segment LED is common cathode, 4 separate digits can be used with segments a to g linked. The seven segments, a to g, of one digit are linked to the corresponding seven segments in the other digits. The LEDs I used are 5621AS. cc1 is the common cathode of the digit on the left.
Total 5V supply current is 30mA.
MAX6675 can be bought from eBay: https://www.ebay.co.uk/

Thermometer based on PIC16F628A and thermocouple module. Included C code and circuit diagram. Displays 0 to 1023 °C .
The temperature is read every 10 seconds, can be changed in the code.
The 7 segment LED is common cathode, 4 separate digits can be used with segments a to g linked. The seven segments, a to g, of one digit are linked to the corresponding seven segments in the other digits. The LEDs I used are 5621AS. cc1 is the common cathode of the digit on the left.
Total 5V supply current is 30mA.
MAX6675 can be bought from eBay: https://www.ebay.co.uk/

Updated on 21/08/24 , old version included in the download.
Thermometer based on PIC16F628A . Included C code and circuit diagram. Displays -55 to 125 °C .
The temperature is read every 10 seconds, can be changed in the code.
The math is using integers to calculate the degrees and the tenths of degrees are calculated separately.
The 7 segment LED is common cathode, 4 separate digits can be used with segments a to g linked.
Total 5V supply current is 30mA.
The 4 digits display is common cathode. The LEDs I used are 5621AS.
cc1 is the common cathode of the digit on the left.
The seven segments, a to g, of one digit are linked to the corresponding seven segments in the other digits.
DP is the decimal point of third digit from the left.
DS18B20 can be any type.