Solarimeter: Sunlight Meter

Summary

My wife wanted to know where best to plant things in the yard, and proposed a device to measure sunlight. I settled on a wifi-based client-server model so I wouldn't have to go out and collect SD cards every day. Each microcontroller has an ID corresponding to its garden bed, and it sends an update to the server every five minutes. The server calculates the hours of shade, sun, and dappled light from the most recent twenty-four hours of data and displays a graph for each bed. You can see the latest data for our garden here.

Hardware

I opted to go for a DIY hardware style this time. Instead of buying the best components made specifically for the job, I'm using cheap parts that I already have on-hand and adjusting for non-linearity in software. Note that the ESP32 ADC is known to be very non-linear.

ESP32 development board with battery. I'm using some prototype boards I made for an electric fence project. A solar cell might be helpful to keep it charged.
Indicator LED to measure brightness. I'm using a red LED with a clear case, but I have a 16oz sour cream container for a diffuser.
Diode and 10k resistor to measure temperature. 1N4148 works fine.
555 timer and a piece of twin-lead to measure soil moisture.
The server is a computer with Docker installed. The operating system shouldn't matter.

Software

ESP-SDK - the base libraries for the ESP32 microcontroller, complete with FreeRTOS
Nginx (in a container
Django (in a Python container)
Postgresql (in a container)
A management container like Portainer is a plus.

Source Code

You can find the esp32 code on GitHub at https://github.com/kamocat/esp32_telemetry

Python/Django code is available upon request.