Si7021 Sensor to Raspberry Pi to PIC to LED

I started this I²C project by creating a simple I²C-controlled LED display using a PIC micro controller. Then I found an I²C Python Raspberry Pi library to communicate with my PIC. The next addition to the mix should be an I²C device I did not create, to verify my code plays well with others.

While talking about I²C at Tux-Lab, one of the past projects came up: a breakout board for the Si7021 temperature and humidity sensor. A unit was brought out for show during this conversation. This particular unit was built a few years ago and has yet to be incorporated into a project.

A web search confirmed this is quite a popular sensor. Lots of sample code and projects. Both Adafruit and Sparkfun sell breakout boards similar to the one Tux-Lab created. And the sensor is also part of the popular Sense HAT. I looked at the data sheet and thought it looked like a good place to start. Best of all, a search for existing code found one in the “Examples” section of the Pi GPIO library I wanted to learn anyway.

I asked to borrow that unused breakout board and added it to my bread board. (Visible in the lower-left of the attached picture.) The additional wiring was trivial, most of the work was on the software side learning Python basics. It didn’t take terribly long to create a rudimentary thermometer. My Python code running on the Pi uses I²C to query the Si7021 for temperature, converted that data for display, and sent that data out the same I²C bus to the PIC.

With the work and learning I’ve put in, I now have an overly complicated contraption that tells me my work space temperature is 75.18 degrees Fahrenheit.

No decimal point on the LED because I ran out of pins on the 18-pin PIC16F1847 chip.


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