I'm a software engineer who just bought a Johnson A419. I have a Nest thermostat.

Naturally, if I can control and monitor my house temps with my iDevices, why not my fermentation?

I'd like to hack together an Arduino (BLE, Wi-Fi, or otherwise) to allow me to monitor/record my fermentation temps remotely, via some manner of connection to the A419. I think I need more hardware info on the unit than just this PDF to do it, though.

Has anyone attempted this, or a similar modification to another controller? Any more in-depth info on the A419 out there?

Or is there a product that already does this? (short of starting from a Nest and working from there, of course)

1 Answer 1


If you're going to go to the effort of including an arduino in the system, then it would be a good idea to also use that for temp control with a more sophisticated algorithm.

The Johnson controllers use simple thermostat algorithm which overshoots on heating or undershoots on cooling, simply because they switch on or off when the setpoint is reached, but already the cool/hot air in the fridge will continue cooling/heating the beer.

The BrewPi project has implemented a predictive algorithm which eliminates over/undershoot. It also has monitoring via a LCD/web UI with temperature graphs. It also supports temperature profiles.

  • 1
    The more I thought about it after posting, the more I figured there wasn't much reason to have the Johnson in the loop at all... an Arduino ought to be just as good at closing relay contacts.
    – Ben Mosher
    Commented Jul 2, 2013 at 17:12
  • If you really want to use the A419, you could use it to control a fridge, which you then simply monitor with brewpi. If you later get a second fridge, brewpi can also control+monitor that.
    – mdma
    Commented Jul 2, 2013 at 20:03

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