Thursday, January 28, 2016

Indoor and outdoor temperature sensors

Similar to my previous build, here are some more temperature sensors using DS18S20 TO-92 case 1-wire temperature sensors.

These are designed to talk to an AVTECH Room Alert system, but would work just as well with any device that can speak 1-wire protocol ( the ends are wired for AVTECH's particular setup. )

I chose the 'S' variant of the 1820 family because evidence suggested that AVTECH used the older devices. Besides, I'm not willing to plug an unknown device into a $1000 monitor without good reason!

Starting the build, I chose some scrap stainless tube, cut down to about 1.5" and cleaned of any flash or other sharp edges that may cut into the cable. A pre-made cap of rubbery plastic serves as the cap to the tube.

The sensors themselves are simply telephone-style cable soldered directly to the devices using "44" core flux, and then cleaned with alcohol. Heat shrink tubing was placed over the individual leads ( be sure to do that BEFORE soldering! ) with larger shrink placed over the whole assembly, leaving the sensor uncovered.

The sensor assembly is inserted into the tube, and the tube is filled with an epoxy. In this case I have access to some industrial materials from 3M, but any good, runny epoxy should do - as long as it's not corrosive to the leads of the sensor. The epoxy is allowed to cure, an RJ-11 is crimped on the other end, and that's it for indoor sensors. They are fairly liquid tight at this stage, but I like to go one more for outdoor use.

For outdoor sensors, I then dip the entire sensor end in tool dip, and allow that to cure. At this point, with the epoxy center and the rubberized overcoat, I'm fairly certain that these will withstand normal outdoor weather. I wouldn't dip it into liquid for extended periods of time, but it would probably work without issues.

Two sensors are now ready to go - one for indoor use and one for outdoor use.

It works! It's actually pretty nice today, for January!

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