notice: this is still a work in prorgess. I try to keep the main branch in a stable state and will try to fix issues if any come up / are reported but I do this in my spare time so...

• abstract
• project setup
  • configuration
• features
  • telemetry topics
  • config topics
  • log topics
  • special topics
• notes
• learnings

This was adpated to work on an ESP 8266 (I used the Huzzah feather) and to add some connectivity. I added:

• MQTT to
  • post the sensor data and ventilation status
  • be able to change settings remotely
• config values are persisted across reboots

sources:

• original project + code from Taupunktlüfter bei heise make
• article in heise make

I used Visual Studio Code with the PlatformIO IDE extension.

Arduino IDE should also work - hasn't been tested (and the folder structure would have to be adapted). The required libraries can be found in the platformio.ini file.

configuration is mainly done in separate header files:

• see src/secrets.h for configuring your WiFi and MQTT server.
• see src/settings.h for configuring the service (offsets, pins etc.)

• MQTT (BASETOPIC can be set in settings.h - if not set it will be omitted.)
  • sensor data
  • config status
  • change configuration
  • heartbeat
  • ventilation status
  • basic logs
• periodic ventilation even when ventilation should not occur according to dewpoints

• BASETOPIC/ventilation/sensor-outside/temperature: Outside sensor - current temperature
• BASETOPIC/ventilation/sensor-outside/humidity: Outside sensor - current humidity
• BASETOPIC/ventilation/sensor-outside/dewpoint: Outside sensor - current dewpoint temperature
• BASETOPIC/ventilation/sensor-outside/heater: Outside sensor - integrated heater status (1 = ON, 0 = OFF)
• BASETOPIC/ventilation/sensor-inside/temperature: Inside sensor - current temperature
• BASETOPIC/ventilation/sensor-inside/humidity: Inside sensor - current humidity
• BASETOPIC/ventilation/sensor-inside/dewpoint: Inside sensor - current dewpoint temperature
• BASETOPIC/ventilation/state: State of the ventilator. Can be ON, OFF.
• BASETOPIC/ventilation/stateNum: State of the ventilator. Can be 1, 0 (with 1=ON and 0=OFF).

All config values can be changed by appending set to the topic.

• BASETOPIC/config/mode: Mode of the dewpoint ventilator. Can be ON, OFF, AUTO.
• BASETOPIC/config/deltaDPmin: minimum difference between dewpoints before ventilator is turned on
• BASETOPIC/config/hysteresis: distance between switch-on and switch-off point
• BASETOPIC/config/tempInside_min: minimum inside temperature at which ventilation is activated
• BASETOPIC/config/tempOutside_min: minimum outdoor temperature at which ventilation is activated
• BASETOPIC/config/tempOutside_max: maximum outdoor temperature at which ventilation is activated
• BASETOPIC/config/correction_temp_inside: offset for inside temperature
• BASETOPIC/config/correction_temp_outside: offset for outside humidity
• BASETOPIC/config/correction_humidity_inside: offset for inside humidity
• BASETOPIC/config/correction_humidity_outside: offset for outside humidity
• BASETOPIC/config/overrideMinHumidity: if the humidity inside is above this value, the ventilator will be turned on periodically to prevent mold
• BASETOPIC/config/overrideMaxHoursWithoutVentilation: after this time, the ventilator will be turned on for at least overrideVentilationMinutes minutes
• BASETOPIC/config/overrideVentilationMinutes: amount of minutes to override the ventilation status

• BASETOPIC/log/startup: startup time in UTC (requires internet to get current time from ntp server)
• BASETOPIC/log/heartbeat: heartbeat timestamp in UTC - sent every 10 seconds
• BASETOPIC/log/ventilatorStatusReason: Reason as string for the current state of the ventilator.

• BASETOPIC/config/reset: set this to 1 or true to reset the config values to the default config (aka what was in settings.h)

• bad WiFi can cause strange things... some values were sent as NaN even though WiFi was connected (lots of packet drops though) and QoS was set to 1.

• don't put the outside sensor close to where the ventilator is. In my case I had it about 50cm from the ventilator and as soon as the ventilator ran, the outside temperature was strongly affected by the air coming from the ventilator.
• think about how to easily update your software during testing (I ran into the basement with my laptop from the 2nd floor about 100 times) -> will look at OTA in the future
• ESP8266 seems to be pretty resistant to interferences. It worked without the preventing measures mentioned in the original article (I only put the 1000 µF capacitor between + and - and left out all other capacitors & resistors that were meant to help with interferences)
• It's really hard to debug issues that come up after longer operation (for some reason I see restarts every few > 5 days and have no idea what it is. My solution for now: design everything in a way that restarts are not a problem)
• the longer I look at code the more ideas I get :-)
• DHT21 sensors are not suite for outside use - humidity clogs up at some point during colder season