GPIO Extension using MCP23017 (CJMCU-2317) on ESP8266

When the ESP8266/ESP32/Arduino lacks GPIO you can use the MCP23017 chip to increase the number of ports by 16. Chip Control is performed on two wires I2C, communication is convenient. The Price for the chip is about $0.8. On Aliexpress is quite a large selection of options chip and two main options boards.

Wemos D1 Mini (ESP8266) is widely represented on Aliexpress at a price of less than 3 USD.

Since the board supports I2C addressing allowing to connect 8 boards, total to the microcontroller it is possible to add 128 GPIO.

Connection Scheme

The MCP23017 Pinup is as follows:

Addressing The I2C board is determined by the closure of the legs A0-2 to + 3.3 V or GND. The Addressing Table is:

Wemos D1 connection Diagram with MCP23017:

Wemos D1 Pin Name	MCP23017 Physical Pin	MCP23017 Pin Name	Description
D1 (SCL)	12	Scl	I/O Serial Clock input
D2 (SDA)	13	Sda	I/O Serial Data
3V3	18	Reset
3V3	9	Vdd	Power
Gnd	10	Vss	Ground
Gnd	15	A0	Hardware Address Pin
Gnd	16	A1	Hardware Address Pin
Gnd	17	A2	Hardware Address Pin

As a sensor, I used a line crossing sensor. The diagram is used as an example of a rain sensor board. The sensor Circuitry is the same, and for fritzing I could not find the libraries for the line crossing sensor.

When the sensor is triggered, the signal arrives at the input GPA0 and ESP8266 lights the LED switched to the output GPB0.

Program

If MCP23017 is connected to ESP8266 correctly, the device will be found when the https://playground.arduino.cc/Main/I2cScanner sketch is run.

11:04:46.058-> Scanning...
11:04:46.058-> I2C device found at address 0x20!
11:04:46.140-> done

When working with MCP23017 through the Adafruit MCP23017 library. will need a table of translation of Adafruit inputs into the names of inputs and the number of legs on the chip.

Adafruit PIN	Pin Name	Physical Pin
0	GPA0	21
1	GPA1	22
2	GPA2	23
3	GPA3	24
4	GPA4	25
5	GPA5	26
6	GPA6	27
7	GPA7	28
8	GPB0	1
9	GPB1	2
10	GPB2	3
11	GPB3	4
12	GPB4	5
13	GPB5	6
14	GPB6	7
15	GPB7	8

The program will also need to address Adafruit, it is different from addressing I2C.

Address I2C	Adafruit Address	A0/P IN 15	A1/P IN 16	A2/P IN 17
0x20	0	Low	Low	Low
0x21	1	HIGH	Low	Low
0x22	2	Low	HIGH	Low
0x23	3	HIGH	HIGH	Low
0x24	4	Low	Low	HIGH
0x25	5	HIGH	Low	HIGH
0x26	6	Low	HIGH	HIGH
0x27	7	HIGH	HIGH	HIGH

The Program accepts the signal from the input GPA0 and lights the LED on the output GPB0 MCP23017 and on the board Wemos D1.

#include &lt; Wire. h.
#include "Adafruit_MCP23017. H"

#define MCP23017_GPA0 0//Digital input on MCP23017 correspond to A0 
#define MCP23017_ADDR 0x20
#define LedPin 2//A0
#define MCP23017_LED 8//GPB0

Adafruit_MCP23017 MCP;

void Setup () 
{
  Serial. Begin (9600);
  MCP. Begin ();      Use default address 0x20

  MCP. pinMode (MCP23017_GPA0, INPUT); Define GPA0 as input pin
  MCP. pinMode (MCP23017_LED, OUTPUT); Define GPB0 as output pin
  MCP. pullUp (MCP23017_GPA0, HIGH);  Turn on a 100K pullup internally
 
  pinMode (LedPin, OUTPUT);  Use the LedPin LED as debugging
 }

void Loop () 
{
  int value_A0 = analogRead (A0); Reads the analog input from the IR distance sensor
  BOOL value_D0 = MCP. digitalRead (MCP23017_GPA0);//reads the digital input from the IR distance sensor
  MCP. digitalWrite (MCP23017_LED,! value_D0);
  digitalWrite (LedPin, value_D0);
  Serial. println (value_D0 + "Value:" + String (value_A0));
  Delay (1000);
}

Connecting the relay to the MCP23017

Illuminated LED-Thing informative, but in life when the sensor is triggered to perform some actions, often physical: something to open and close, move, etc. So connect the relay to the LED.

As for relays and selection for microcontrollers-this is a topic for a separate article, the options are many and there are nuances. For a long time not to be wise, connected to the MCP23017 “native” relay sharpened under the Wemos D1 Mini. Such relays are inexpensive, widely presented by sellers on Aliexpress, supports TTL level 3V, i.e. Do not need to put a converter levels 3V <->5V.</->

Actually, it is easy to connect it. The Control goes on high level, i.e. On the 1-St at the control inlet D1. If It was a low level trigger, in the software it was necessary to put inversion on logic that inclusion was on 0-th, and disconnection on 1-th on input of control. And, not for all relays the program inversion works.

In general, in order not to have problems when connecting the relay to the microcontroller, working on the voltage 3.3 V, with the appropriate level of TTL logic, you need to: