Home > Prototyping, Tech geeks, Temperature monitoring > Temperature Monitoring Prototyping is Winding Down

Temperature Monitoring Prototyping is Winding Down

prototype 20140823Today I wrapped up prototyping activities for my bluetooth carboy temperature monitoring system. As a somewhat last minute decision I added a local LCD display that cycles through and shows the last values for each sensor and when the reading was taken. I realized it would be kind of dumb to require sitting at the PC or logging in with a smartphone to see what the current temperature readings are, especially when you are down next to the carboys while they are fermenting. There happened to be a little bit of extra memory and several digital pins left unused on the Arduino, so squeezing in the LiquidCrystal code was not too much of a problem. To see it in action, check out the video below.

The Arduino program code was re-written from almost the ground up to allow the sample frequency and “friendly name” to be configured for each sensor individually and to log the sample data in individual files. The sketch / code is available here on my OneDrive. It currently lacks sufficient comments / documentation, but I’ll get to that soon (provided I don’t need to do additional tweaks).

One of the issues I have been concerned about is creation of the temperature sensors. I have many of the TO92 package DS18B20 temperature sensors laying around, but having to solder them to 3 conductor wire, make them semi-waterproof, and connect them reliably to the main unit had me worried. I found several places online to purchase them in waterproof packages with wire attached, but typically they were >$10/ea, which is pretty steep for just 6 feet of wire. After some digging around online I happened upon these awesome waterproof DS18B20 sensors from YourDuino.com, and their 10m brothers. At $4/ea and $8/ea respectively, they are much more affordable than the state-side alternatives, even after DHL shipping from China. I’ve tested most and every single one has performed as expected.

20140823_175858Next I had to find a thermowell that would fit the sensors with their waterproof stainless probe. These were smaller in diameter than the other waterproof ones I saw online, but they still didn’t fit in the thermowell I purchased several years back from MoreBeer.com. This is frustrating because I paid $25 for a (useless) piece of equipment, and the size probe that would fit would have to be tiny… so back to the internet I went in search of alternatives. I scored big. I stumbled into these from Brewers Hardware, which not only have a larger internal diameter, but are higher quality and less than half the price. I still need to take a trip to the local homebrew store and pick up some undrilled carboy stoppers to use with them, but that will be a very small investment. The picture to the left shows a comparison, with the MoreBeer thermowell on the right and the Brewer’s Hardware ones on the left. I must say this is the first area that MoreBeer has really let me down – most of my equipment has been purchased from them.

 

sensor plugs markupI settled on using 3.5mm audio plugs for the connection between the device and the sensors. They are impossible to connect backwards, and support a 3 conductor wire which is exactly what the DS18B20s need. I purchased some inexpensive 3.5mm plugs from SparkFun.com which seem to work perfectly. The picture to the left shows how I chose to connect things – VCC at the tip, signal on the middle ring, and GND at the back.

I’ve assembled 5 of the cables – basically all the plugs I ordered – and they all seem to work, at lengths of 1m all the way up to 10m. I’ve labeled them with their unique address on pieces of painters tape (for now) so I can easily tell which sensors go into which carboys, once I get everything pulled together.

20140823_180101

Next steps are to work up a printed PCB and get it manufactured by OshPark.com while the programming undergoes some stress testing. Then I assemble everything and fit it into the awesome project box I got for it. I also need to write a PC-side interface to configure the sensors and download the data files. Currently the only means for doing that is through a Bluetooth terminal application or connecting a USB COM bridge directly to the Arduino. The screenshot below shows output after sending a “c” command to get the current configuration settings for all sensors, and the “d2E61” command to download the data file for the “Cherry Lambic” sensor. You will notice that there were several samples taken before the “Cherry Lambic” name shows up – this will allow me to separate data from subsequent batches if I reuse a sensor.

bluetooth terminal

I am very pleased with how this project is shaping up – it may be one of my favorites so far.

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