120. ESP8266 boards
Many boards are available with ESP8266.
They can be equipped with a usb port or not, support different voltages, etc.
I have successfully tested the Xiot framework on the five boards on this picture.
The tiny one on the right (#5 on the picture) is an ESP-01 board (with an ESP8266 chip) would be best fitted for the master module, "iotinator", since it only exposes 2 gpio, which can be used to drive the Oled screen, and the master module doesn't need other inputs or outputs, at least as long as it does not support a GSM board. Or for a module with no screen.
But its RX/RX pins can also be used as I/O pins. You could leave TX to get the debug messages on serial, and use RX as output, I've tried it to run an iotSwitch agent module successfully.
The ESP-12 (#4 on the picture) is a nice alternative since it comes without a soldered connector and exposes many more IO pins, but pin spacing is 2mm (not 2.54mm) so you'll either need an "adapter" board for breadboard/prototyping PCB or design your own PCB.
The downside of these 2 boards being that they require some wiring to flash them since they only handles 3.3V both for power and RX/TX. Although it's not difficult to do, you can also buy USB adapter boards that will allow you to flash them very easily, and it's even cheaper!
| Breadboard circuitry to flash an ESP01 board | All in one USB adapter (US $2.52 free shipping) |
|---|---|
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Even if you solder the board to some other circuitry, it might still be possible to flash it (depending on the surrounding circuitry)
The price tags range from less than $2 for the ESP01 to around $4 for the D1 mini pro if you buy them from China on ebay.com
Here is the master running on ESP01:
Here are 4 agents connected to one master:
As you can see, the master on the left says 4 modules connected. I flashed one more module, and was able to check that "only" 4 modules can connect to the ESP8266 Wifi Access Point.
Which is why I plan to give agent modules the ability to open their own Access Point and act as master proxys to connect yet again more modules!
An improved version of the ESP8266 is available for a while, it's faster and with more memory, but it also consumes more power.
Xiot is not working on ESP32 boards (yet), because of unavailable libraries at the time I tried, but I didn't investigate much, I plan to do it at some point, but there is so much to do :)
One of the available ESP32 board comes with an already mounted Oled screen:
