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Digital Thermometer

Arduino code for a digital thermometer (temperature, humidity and heat index) with auto-OFF functionality.

 

This project use the following electronic components:

  • 1 x Arduino UNO / Nano v3
  • 1 x DHT11 temperature/humidity sensor
  • 1 x 3461BS-1 display (4 digit, 7 segment multiplexed display)
  • 8 x 1k ohm resistors
  • 1 x 10k ohm resistor
  • 1 x Transistor BC547 NPN
  • 1 x Electrolitic capacitor 470uF 10v
  • 1 x Push-button
  • 1 x Batery 9v

The circuit:

  • Pressing the push-button charges the capacitor and puts the transistor in conducting state.
  • After the button is released, the capacitor continues to power the base of the transistor for around 20 seconds.
  • The current through the transistor powers the Arduino (and rest of the thermometer).
  • Arduino constrols the temperature+humidity measurement and the multiplexing process for the 4 digit display.

Notes:

  • This thermometer automatically turns off approximately 20 seconds after activation.
  • To increase this time, change the capacitor to one of higher capacitance.

 

Screenshots

Diagram - Schematics 01 Diagram - Schematics 02
Diagram - Physical Layout Prototype
Building 01 Building 02
Building 03 Box Shaping
Project Final Project Final (YouTube video)

See 'Rescources' sub-folder for more pictures & videos of the project.

 

Version History

v1.0 (2022.12.08) - Initial release.
v1.1 (2022.12.10) - Re-arrange LEDs pin-out to simplefy PCB.
v1.2 (2022.12.11) - Using masked bits to improve character display.
v1.3 (2023.03.28) - Use of headers for better readability.
v1.4 (2023.04.08) - Hardware re-desing.

 

This source code is licensed under GPL v3.0
Please send me your feedback about this project: andres.garcia.alves@gmail.com