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