Using the ESP8285 M3

Chinese webshops sell the ESP-M3. This is a tiny module containing an ESP8285. In short, an ESP8285 is like an ESP8266 but with 1Mb memory on chip. It is for instance the chip that has been used in the SonOff basic till now. The M3 is not a new module,it surfaced in 2016 and was primarily meant for wearables I think.

Sadly it is not really breadboard friendly. 6 pins have a 0.1″ pitch with throughholes, but 6 other pins have a 0.1″ pitch with edge-pads. The alignment between the three rows of  pins is a stretch to fit a standard 0.1″ pitch grid.
The module has the following pins.

ESP-M3	Compares with Wemos/NodeMCU
GPIO0	D3
GPIO1	Tx
GPIO2 (Tx1)(apparently connects to an onboard blue LED	D4
GPIO3	Rx
GPIO4 (VSDA)	D2
GPIO13 (Mosi)	D7
GPIO14 (SCK)	D5
GPIO16	D0
EN	CH_PD
RST	RST
Vcc	Vcc
Gnd	Gnd

The function of the pins is equal to that of the ESP8266. In comparison with the Wemos D1/ESP8266 (11 I/O pins, one ADC pin) the ESP-M3 has only 7 I/O pins, and no ADC. The ESP8285 HAS more pins than that, but these are not all broken out on the ESP-M3 module. All in all that is still 3 pins more than the ESP8266-01.

As the GPIO16 pin is broken out, the M3 board is more flexible in DeepSleep applications.

The use of the ESP-M3 is similar to that of the ESP8266. In order to go into Flash mode, the GPIO0 pin has to be made LOW. For ‘normal use’ the GPIO0 has to be pulled HIGH. The EN pin has to be pulled high. Choose 8285 board for upload. An ESP8266-01 programmer can quickly be repurposed to program the M3.

void setup() {
pinMode(2, OUTPUT);
}

void loop() {
digitalWrite(2, HIGH); // turn LED on 
delay(500);
digitalWrite(2, LOW);
// turn LED off
delay(500);
}

There is a Wiki with user manual.

A minimal system is built like this:

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