I received the Johnson A419 Digital Temperature Controller and will be getting a Fermwrap today in the mail (and I will be brewing tonight hopefully).

I noticed that the Johnson model comes with a probe. Do I sanitize this probe and place it through the airlock into my wort?

I currently use a Raspberry Pi with DS18B20 temperature probes to monitor the temperature of my wort, which I store in a database. I sanitize these probes and place it through the airlocks into my wort.

I would not be able to fit both the DS18B20 and the Johnson probe through the airlock as the diameter isn't big enough.

Must I sacrifice my statistical experiment to accomodate the Johnson probe?

On the other hand, is there a way for me to put the Johnson probe through the airlock and then read send the temperatures from the Johnson Control to my Raspberry Pi (Or first to my Arduino and then to my RPi)?

Any ideas?

1 Answer 1


AFAIK, the Johnson probes are not waterproof, so you should not place them into the wort/beer. Either get a thermowell so you can read the temp of the beer itself (ideal), or tape the probe to the outside of the carboy. If you do that latter, you can continue to use your RPi recording approach on this brew.

Going forward, you have a number of options…

1/ Extend the RPi to drive a relay to drive the fermwrap, and use that to obsolete the Johnson A419.

2/ Drop two thermowells into the carboy so you can both control (via A419) and record (via DS18B20+RPi).

3/ As you say, try to read the temps off the A419's probe.

  • Good point about it not being water proof. Jan 11, 2014 at 23:35
  • Would you mind expanding upon option number 1 so I know what to Google? That would be very exciting to use the RPi INSTEAD of the Johnson A419 Jan 12, 2014 at 0:01
  • 1
    Another option is to use brewpi - raspberry pi fermentation controller. brewpi.com
    – mdma
    Jan 12, 2014 at 3:59
  • If you tape the probe to the outside of the carboy, most people will recommend taping some sort of insulation to the outside of the temperature sensor so it is picking up wort temperature instead of ambient temperature. Jan 12, 2014 at 21:31
  • As an update, I bought multiple "PowerSwitch Tail II"'s and now control the temperature with my RPIs alone. I'll keep the johnson for when I buy a refrigerator to brew in. Mar 25, 2014 at 4:14

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