Last Updated or created 2023-03-07

Warning, read the notes!

There are several caveats.

• I was needing ALL GPIO pins, even RX/TX ( see trick below)
  When doing so, you can’t use serialprint.
  Do NOT enable, your sketch won’t work!
• Don’t use pullup on D8, you can’t upload to the wemos if you do that
• Due to library conflicts in keypad.h, DON’T change the order in the source. You will end up with compile errors!
• The keypad has a weird pinout, but there are similar keypads with alternative layouts. Measure this using a multimeter.
• The pull-up resistors will help fighting ghost key presses!
• I2C needs D1/D2

To use RX/TX as GPIO pins you need to do the following:

//Define pins
  int led = 1; //tx
  int col = 3; //rx

// Change to function mode 3
// see https://www.esp8266.com/wiki/doku.php?id=esp8266_gpio_pin_allocations
  pinMode(1, FUNCTION_3);
  pinMode(3, FUNCTION_3);
 
// Revert to normal mode
// pinMode(1, FUNCTION0);

// Define mode input/output
// i'm using led to control the led so thats an output
// I'm using col for the keypad column scanner, that's an input
  pinMode(led, OUTPUT);
  pinMode(col, INPUT);

Complete code

The (*) clears input
The (#) sends the pin code using MQTT

Sending a 0 or 1 to escape/keypadin topic will toggle the led

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <WiFiClient.h>
// Do not change order!
#include "Keypad.h"
#include <TM1637Display.h>
#include <Ethernet.h>

#define wifi_ssid "SSID"
#define wifi_password "SSIDPASS"
#define mqtt_server "MQTTSERVER"
#define mqtt_port 1883

#define MSG_BUFFER_SIZE  (50)
char msg[MSG_BUFFER_SIZE];
int value = 0;

const byte ROWS = 4; //four rows
const byte COLS = 3; //four columns

int led = 1; //tx
int col = 3; //rx

#define CLK D1
#define DIO D2
#define TEST_DELAY   2000
TM1637Display display(CLK, DIO);

char keys[ROWS][COLS] = {
  {'1', '2', '3'},
  {'4', '5', '6'},
  {'7', '8', '9'},
  {'*', '0', '#'}
};
byte rowPins[ROWS] = {D3, D5 , D6 , D7 };
byte colPins[COLS] = {D4 , col, D8 };

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
int keyNum = 0;
WiFiClient espClient;
EthernetClient ethClient;

PubSubClient mqtt(espClient);

void setup_wifi() {
  delay(10);
  WiFi.mode(WIFI_STA);
  WiFi.begin(wifi_ssid, wifi_password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }
}


void setup() {
  setup_wifi();
  mqtt.setServer(mqtt_server, mqtt_port);
  mqtt.setCallback(callback);
  
  pinMode(1, FUNCTION_3);
  pinMode(3, FUNCTION_3);
  pinMode(led, OUTPUT);
  pinMode(col, INPUT);
  // using above? .. then disable serial!
  // Serial.begin(9600);
display.showNumberDec(0, true);
delay(TEST_DELAY);
WiFiClient espClient;
PubSubClient mqtt(espClient);

 mqtt.setClient(espClient);
 mqtt.setServer(mqtt_server, 1883);
    
mqtt.setCallback(callback);
mqtt.subscribe("escape/keypadin");

}

void callback(char* topic, byte* payload, unsigned int length) {
    //  digitalWrite(led, HIGH);

    String topicStr = topic;
      byte value = atoi((char*)payload);
       if (value == 1){
    digitalWrite(led, HIGH);

 }else if (value == 0){
    digitalWrite(led, LOW);
 }
    

}

void reconnect() {
  while (!mqtt.connected()) {
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    if (mqtt.connect(clientId.c_str())) {
      mqtt.publish("outTopic", "hello world");
      mqtt.subscribe("escape/keypadin");
    } else {
      delay(5000);
    }
  }
}



void loop() {

  if (!mqtt.connected()) {
    reconnect();
  }
    mqtt.loop();

  // put your main code here, to run repeatedly:
  char key = keypad.getKey();

  if (key) {

    if(key=='*'){
      keyNum = 0;
    } else if (key=='#'){
         ++value;
  snprintf (msg, MSG_BUFFER_SIZE, "#%1d", keyNum);
        mqtt.publish("escape/keypad", msg);
    }
    
       else{
      if(keyNum<=999){
        keyNum = (keyNum*10) + (int(key)-48);
      }
    }
    
    //  Serial.println(key);
    display.setBrightness(0x0f);

    uint8_t data[] = { 0x0, 0x0, 0x0, 0x0 };
    display.setSegments(data);

    display.setSegments(data);
    display.showNumberDec(keyNum);

  }

}