Difference: WeMosD1Mini (6 vs. 7)

Revision 72019-05-07 - UliRaich

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The WeMos D1 mini and its sensor and actuator shields

Introduction

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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

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ESP8266

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

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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.

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ESP32

As an alternative you have a CPU board based on the more powerful ESP32:

As for the ESP8266 there is a Micropython port for the ESP32. The drivers are essentially the same, the pinout of the board however (GPIO numbers for the pins) is different. This means that for every driver we must only change the GPIO number. Since it is possible to find out from Micropython on which platform we run (sys.platform tells you if your CPU is a "esp8266" or a "esp32") we can check for the CPU type and adapt the pin numbering as a consequence.

Here is a comparison of the pin assignments for the 2 CPUs:

ESP8266

	RESET	RST	Tx	GPIO 1
	ADC0	A0	Rx	GPIO 3
SCK	GPIO 16	D0	D1	GPIO 5	SCL
MISO	GPIO 14	D5	D2	GPIO 4	SDA
MOSI	GPIO 12	D6	D3	GPIO 0
SS	GPIO 13	D7	D4	GPIO 2
	GPIO 15	D8	GND	GND
	3.3V	3V3	5V	5V

ESP32

	RESET	RST	Tx
ADC1 channel 0	GPIO 36	SVP	Rx
	GPIO 26	IO26	IO22	GPIO 22	SCL
SCK	GPIO 18	IO18	IO21	GPIO 21	SDA
MISO	GPIO 19	IO19	IO17	GPIO 17
MOSI	GPIO 23	IO23	IO16	GPIO 16
SS	GPIO 5	IO5	GND	GND
	3.3V	3V3	5V	5V

Sensor Shields

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:

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