Build requirements:
- Arduino IDE 1.8.13
- Arduino ESP8266 package 3.0.2
- Arduino library ESPAsyncTCP https://github.com/habazut/ESPAsyncTCP/tree/fix
- AsyncMqttClient library https://github.com/marvinroger/async-mqtt-client.git
Needs a credentials.h with
#define WIFI_SSID "FOO"
#define WIFI_PASSWORD "BAR"
Hardware (schematics etc) found on: https://github.com/psvanstrom/esphome-p1reader