This project is an example of how to use a board with many I/O-pins, a temperature sensor and a digit display to build a thermometer. My version updates every 10 seconds.
The digit display does not have an anode for each segment it has. Instead, just 8 of its pins are anodes, connected to the same segment of the 4 different digit-parts.
The other 4 pins are the cathodes. One for each digit-part.
But now it is only possible to display the same digit on 4 digit-parts (e.g. "2222", "7777"). That sucks, right? There is a special method to address this problem.
The solution is to iterate over the digits of the number to display, show only one digit at a time and ground the correct pin by applying voltage to the base of the desired transistor. This process will repeat so often and so fast that the human eye is unable to see the flickering. If desired, it is possible to make the flickering visible by adding a little delay (e.g. 10ms).
The temperature is read via the I²C interface. If the initial connect fails, the display will show "FAIL".
My code is available in the TempDisplay.ino file.
The required components are:
- Board with many I/O-pins: LOLIN D32 Pro V2.0.0
- Temperature sensor: GY-BMP 280
- Digit display: 7+1 segment SH5461AS
and
- Resistors
- 8x 75Ω (for the digit display)
- 4x 10kΩ (for the transistors)
- Transistors
- 4x BC547
The components can be substituted, these are just my recommendations. The 3V or 3V3 pin of your board should be used. The temperature sensor will run on 3.3V, but the display can only handle 1.8V.
Here is a schematic I created in KiCad:
Note that I didn't use 8x 75Ω resistors, because I didn't have them handy. Instead I just used one 220Ω resistor, which is bad, but it works.
