There are so many out there now. I thought I would pick the brains of the experimenters familiar with them.
I was going to use an Arduino Nano for my project but it runs on 5V and my solar cell supply is good for about 4V.
In this way it is self-contained and battery free. (Only needs to work during mid-day.)
So here are my desired traits:
-Will run on 3.3 Volts.(power is 4.5V max solar cell charging a 1.5 Farad capacitor)
- Is mounted on a board with required peripheral chips like a Nano
- Can be programmed with Python or microPython (I don't like antiquated C and Python looks learnable).
- Board size about the same as a Nano.
- Can communicate easily with I2C sensors
- Low complexity and low cost

My application reads a humidity/temp sensor board like the SHT31 (link below) and inputs the data into an RF transciever
such as the HC-12 (eBay). Initially I was hopeful that I could find a sensor that would just power-up sending humidity
and temperature data that I could wire directly into the transmitter but I can't so I need a simple micro between them.
Do I need a zener diode to limit the input voltage to 3.3V? or is 4V OK. I have never used a 3.3V device.
Sensor link: https://www.adafruit.com/product/2857 This sensor has a fast 1 second response time which I need.
HC-12 data sheet attached.
Thanks for your assistance!

 

Humm. I think you have made your choice already.

 

Since no one was brave and suggested a processor I took a stab at the market and came up with a candidate.
Adafruit seems to have embraced the Python and microPython language and offers several alternatives.
The one I picked is the Trinket M0 which is only $9, is based on an ARM M0 processor from Microchip (formerly Atmel).
It comes loaded with an easy to interface method that allows one to plug it into your USB port. It shows up as a USB memory
on your PC. If you store a Python code file named CODE.PY to this "memory stick" it immediatly runs it! It is way faster,
than an Arduino but has far fewer available general I/O pins. All comm is by serial, I2C or SPI.
Now I have to plug away at learning Python. Just got a book from the library, Learning Python, and it is 1500 pages!

 

Good luck on your project.