I recently played around with mqtt again and used one of my #Ignore this ESP8266 board -s to internet-of-thingify this fan construct. Searching for reasons why the uln2004 wouldn't work with 3.3V I tried pnps and npns until I found that I haven't declared the pins I was using as an output. I might have also connected the 12V with the 3.3V line while experimenting :D but in the end it turned out that I had also connected the fans backwards. Muah. But now it runs and I can control it via MQTT.fx - winning.

The ESP arduino soft PWM runs at 1kHz and I can hear it, that is kind of annoying.

Don't forget to set different clientIDs ;)