Build with Ardunio IDE and Board Extension ESP8266WiFi
https://github.com/esp8266/Arduino // http://arduino.esp8266.com/stable/package_esp8266com_index.json
Using the following pins:
| Function | Pin | Description |
| Force WLAN Config | D4/GPIO2 | Causes acess point to open for WLAN config during normal operation |
| Transmitter | D6/GPIO12 | |
| USB/Flashing | D9/GPIO3 | fixed pin |
| D10/GPIO1 | fixed pin | |
| Required for reset | D8/GPIO15 | must be low for reset (bad with I2C pullups) |
| D4/GPIO2 | sometimes used for buildin LED (must be high for reset) |
|
| D3/GPIO0 | must be low for reset |
Libraries required:
| WiFiManager.h | https://github.com/tzapu/WiFiManager |
| ArduinoJson.h | https://github.com/bblanchon/ArduinoJson |
| Adafruit_MQTT.h | Required Adafruit MQTT Lib Version >=0.16.1 |
| RCSwitch.h | https://github.com/sui77/rc-switch |
Sorcecode is available at https://github.com/FoxRomeo/ESP-MQTT-433MHz
For the hardware use any ESP8266.
For beginners use a module with "buildin" USB (Like NodeMCU or WEMOS D1 mini or D1 minipro).
The transmitter MUST be operated with 3.3V (therefor the most "Arduino transmitters" don't work) and you MUST attach an antenna (at least a cable with exactly 17,3cm).
If you coil up the antena you reduce range (or use one of the listed below).
For Gemany:
ACHTUNG! Stellen Sie vor Inbetriebnahme sicher, diese nur mit der zulässigen Sendeleistung zu betreiben. Die aktuellen Bestimmungen können unter www.bundesnetzagentur.de überprüft werden.
https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Allgemeinzuteilungen/2003_76_ISM_pdf.pdf;jsessionid=26A12072F86B6B3DECFD82321C669DA9?__blob=publicationFile&v=5
For other countries:
Check your allowed frequency (mostly 433MHz or 315MHz), max transmitting power (for example in Germany 10 mW) and what other laws you have to follow.
Easiest way: Use only official and licensed modules for your country , no self build stuff.
Hardware examples (only examples, I used other parts, but don't have the links anymore):
ESP8266
https://www.amazon.de/WeMos-mini-8266-NodeMCU-Arduino/dp/B01I1CIHDA
https://www.amazon.de/ELEGIANT-NodeMcu-ESP8266-ESP-12E-Development/dp/B018E741G4
433MHz transmitter
https://www.amazon.de/gp/product/B00V4ISS38
https://www.conrad.de/de/sendemodul-aurel-tx-saw-mid3-v-15-vdc-35-vdc-191511.html
antena
https://www.amazon.de/gp/product/B00SO651VU
Update:
If your skills with hardware and/or soldering iron are limited, but you know how (or want to learn (are not afraid)) how to flash a firmware try the SOnOff RF Bridge 433.
I can only ensure you to flash it with a new firmware from Tasmota.
I will soon write how to use this Bridge with MQTT and 433MHz devices like Pollin Funksteckdose (550666). (It's a bit tricky to calculate the first values, but after that... easy going.)