The WeMos D1 mini and its sensor and actuator shields

Introduction

We have seen that the ESP01 can be programmed with micro Python and that there are add-on sensor boards available. However, when we connect the sensor board we loose the serial connection to the PC. This can be corrected by soldering extra connectors to the top of the ESP01 board but this is fiddly and needs good soldering equipment and good soldering skills. The other option is to get access to the ESP01 through WiFi using WebRepl

A better and only slightly more expensive solution (we are talking about ~ 3.5 US$ instead of 2.5 US$) is the Wemos D1 mini board. This boards gives up more I/O connections and many more sensor and actuator shields are readily available on the market.

The processor board

The processor board uses an Espressif ESP8266 processor chip and 4 MBytes of flash are installed on the board.

You will find a description of the pinout at https://www.likecircuit.com/wemos-d1-mini-pinout

For convenience I copied the basic information here.

In contrast to a PC the WeMos D1 mini has only very limited memory resources. While 4 MBytes of flash memory is rather comfortable, the amount of RAM (80 K) is a very limiting factor. When running micro Python a mere 30 kBytes is left for your Python programs. There are essentially 2 ways to make most out of the small amount of RAM:

• You can pre-compile your programs to byte code, which takes less space in RAM
• You can code freeze driver libraries, which means you integrate their byte code into The micro Python image. This however means that you must compile your own version of micro Python and flash it into the WeMos D1 CPU.

A big number of sensor and actuator boards are available. You will find a complete list with their description at https://wiki.wemos.cc/products:d1_mini_shields

Here are the sensor shields and their test programs for the workshop:

• The triple base and prototype boards
• A simple Pushbutton Switch
• The WS2812B rgb LED
• The DS1307 real time clock and data logger
• The buzzer shield
• The bmp180 shield featuring an atmospheric pressure and a temperature sensor
• The Oled shield
• The DS18B20 shield with a Dallas DS18B20 1-wire digital temperature sensor
• The LED matrix shield
• The SHT-30 shield with a SHT-30 I2C digital temperature and humidity sensor
• The DHT11 shield with a DHT11 digital temperature and humidity sensor. This device uses its own private serial communication protocol

Here is an overview table showing the devices and the

Module	Connections	Functionality
1 button shield	D3: GPIO 0	on / off push button
WS2812B RGB shield	D2: GPIO 4	addressable rgb LED
DS1307 RTC and data logger	D1: GPIO 5 I2C SCL D2: GPIO 4 I2C SDA D5: GPIO 14 SPI Clock D6: GPIO 12 SPI MOSI D7: GPIO 13 SPI MISO D8: GPIO 15 SPI CS	Real Time Clock SD card interface
Buzzer shield	D5 (default GPIO 14 D6 GPIO 12 D7 GPIO 13 D8 GPIO 15	passive buzzer
BMP180 shield	D1 GPIO 5 I2C SCL D2 GPIO 4 I2C SDA	I2C barometric pressure sensor and temperature sensor
DHT11 shield	D4 GPIO 2	temperature and humidity sensor
OLED shield	D1 GPIO 5 I2C SLC D2 GPIO 4 I2C SDA	64x48 pixel display with SSD1036 I2C controller
DD18B20 shield	D2 GPIO 4	1-wire digital temperature sensor
SHT30 shield	D1 GPIO 5 I2C SCL D2 GPIO 4 I2C SDA	I2C temperature and humidity sensor
LED Matrix shield	D5 GPIO 14 CLK D7 GPIO 13 Din	8x8 LED Matrix

ir connections:

For each of the devices I create 2 directories:

• a driver directory containing programs testing the module without Cayenne communication
• a cayenne directory for the final program

You can find the code written for the workshop on github: https://github.com/uraich/MicroPython_IoTDemos.

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