Home > Prototyping, Tech geeks, Temperature monitoring > Wireless Fermenter Temperature Monitoring (Part 1)

Wireless Fermenter Temperature Monitoring (Part 1)

Several months back a friend who knows I tinker in this nerdy electronics stuff asked me if I could develop something to help him monitor and log fermenter temperatures. My off-the-cuff answer was “of course, lemme think on it and I’ll get back to you”. At the time I was pulling BrewzNET 2.0 together and devoted most of my energy to getting that project completed… so the fermenter temperature thing was put on the back burner. Every once in a while I’d put enough thought into it to ask him some additional meaningful questions, or add my own wants/wishes to the list, and ended up with a rough requirements list:

  • Better than 10 bit temperature resolution
  • A new reading every 5 minutes or so
  • Ability to either store data until a PC is connected, or store data on removable media, or send the data to the PC wirelessly
  • Expandable to more than one fermenter
  • Must fit in the thermowell with another sensor

Unfortunately that last one nearly killed the project (at least for my friend), because I have very limited options when it comes to temperature sensors. I decided this was something I wanted for my own homebrewing setup, so I’ve continued on hoping that once I’ve got a design put together he may still be interested in it.

My tentative plan is as follows:

Why these particular components?

  • The 3.3V Arduino Pro Mini is the obvious choice as all of the other components require 3.3V power, and using a 5V microcontroller would mean oodles of level-switching as well as a second power regulator to step the 5V down to 3.3V – It makes more sense to run everything on 3.3V.
  • The DS18B20 sensor makes the most sense in this application. It’s digital which allows longer wire runs than an analog sensor and I do not have to worry about significant signal degradation / resistance losses. It works just fine at 3.3V. It also has a better resolution than the typical 10-bit analog devices. You can also put multiple devices on the same one wire bus, which means it is expandable.
  • Bluetooth seemed to make more sense than other wireless technologies, like an Xbee, because it is really just a 2-device connection – the PC and the temperature logger. My understanding is that Bluetooth is also a relatively robust protocol for sending data – it must be considering all the devices out there that use it.
  • The MicroSD card seems like “extra”, but after thinking about my own experience with PCs and trying to log data to them, I realized redundancy is always a good thing. Our PC seems to lock up / crash with a greater frequency than I would like, and depending on the power settings it could be in “sleep” mode and miss data. Very few people have their PCs running 24/7, so while a Windows service could capture the communications and data “behind the scenes”, that strategy only works if the PC is running (and running reliably).

I am still trying to figure out if I need a RTC (real-time clock) like a DS1307 to pair date & time with the temperature readings. Setting the clock becomes the issue, if so… Maybe it sets the clock when the Bluetooth pairing with the PC occurs? I just don’t know yet.

 
wpid-20140705_070936.jpgTemp Proto Output
 

This morning I was successful in putting together a basic circuit with four DS18B20s and read their data. The Arduino program was pretty easy since I just tweaked the example sketch that comes with the OneWire library, so someone else had already done the heavy lifting. The example program was comprehensive enough to support multiple sensors, so all I changed was some of the serial output and the 1-wire bus pin. The screenshot shows the four different devices (and their hexadecimal addresses), the raw data for each, and the data converted into Celsius and Fahrenheit readings.

The sensors are all configured to run off “parasite power” which means the data line charges them up when readings are not being taken, and only two wires will be required for each sensor – a ground (going to the two outer sensor pins) and a data line (the middle pin). I am going to experiment with different gauges of wire and try to get it as thin as possible in the hope that my friend will be able to use this sensor, even with his big Ranco temp controller sensor shoved in there.

The next stage will probably take the most time – getting the Bluetooth communications set up and the MicroSD card interface working. Both of these areas are brand new to me so I’ll have a learning curve to slog my way up. Fortunately the MicroSD card breakout has an excellent tutorial associated with it, and the Bluetooth COM stuff seems pretty straight-forward. I wanted to play with the Bluetooth stuff prior to posting but unfortunately the Bluetooth adapter that serves as the PC interface side has gone missing. Hopefully it will turn up soon.

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