In this project, I'm designing a WiFi-connected PCB that adds remote control capabilities to an old-school Venta LW 45 air humidifier.

The control panel - connected to the main PCB via a 10-pin ribbon cable - of the humidifier provides five LEDs indicating power status, level and error and two buttons to turn the device on/off and to change levels. I insert my own custom PCB where the ribbon cable is plugged in, thus allowing me to read out the HIGH/LOW status of each cable pin as well as pulling down each cable pin emulating a button press.

As the Venta LW45 is powered through an external 24V power supply, I tap into that power source, but need to convert to 3.3V for the ESP8266 that is used to provide the WiFi control. To read out the status of the LEDs, I use LM339 / LM393 dual / quad differential comparators and to emulate button presses, I'm using three 2N7000 FET transistors.

Although I initially intended to use an ATmega328P with a nrf24l01+ SMD 2.4GHz module to connect the Venta humidifier to MySensors, I finally decided to go with a ESP8266-12 WiFi module instead. The schematics, a prototype on breadboard and the source code for the MySensors version all exist and can be downloaded (For the link see my blog post about this whole project: http://wiki.kainhofer.com/hardware/venta_connected). Only the PCB design is NOT finished / optimized in that version.

The version presented here uses the ESP8266-12e/f, is fully designed, PCB is finished (I didn't yet receive the PCBs for the latest version that includes pull-downs with the FET gates, but I'm using the previous version without problems) and the firmware for the ESP is also finished (custom Venta plugin for ESPEasy is available in the ESPEasy playground).