Wednesday, August 23, 2017

Room Temperature Sensor; got to use the 3D printer for real

I used my 3D printer on a real project, the room temperature sensor. I spent a ton of time messing around with various drawing tools and learning a little about slicing software, but didn't actually do anything that could be considered useful. Unless you count a stand for my Star Trek Enterprise that I have on the kitchen window sill:

I got the files for the stand off Thingiverse <link> and just printed it. Thingiverse is wonderful for getting things that other people have worked on, but it isn't the same as coming up with your own idea and stepping through the entire process.

I decided on the basics of an enclosure for the sensor weeks ago, but it took a while to decide on a tool to use to design it, then the actual design process. I tested a couple of enclosure ideas for a few weeks and finally, a couple of days ago, put four more of the sensor electronics together and printed enclosures for all of them. I have five areas of the house being monitored and recorded in my home database that I can chart and examine.

Yes, they follow each other really well over the period charted, but remember, a temperature change of a small amount will make a room feel hot. It's interesting to watch this phenomenon. One room is 75F and the next is 78F, not enough to matter, but it feels really hot in the warmer room. It doesn't help much to put a thermometer in the warmer room so you can see the actual temperature; you just think the thermometer is wrong. Strange.

Here's what the entire assembly looks like on the wall:

It consists of a base plate that you mount to the wall and a cover that slides over the base to protect the wiring. Here's the two pieces before mounting:

Most of the engineers out there could have drawn this up in about 10 minutes, but frankly, this process was tough. Every little item had to be measured and thought out carefully. I had many, many test prints of sections to see if various things actually fit together. I kept running into little unexpected problems. The plastic would be a little too rough in some spots and pieces wouldn't fit together. The model would glue itself to the base of the printer and it flatly refused to come off. I didn't put holes in the sensor PC board and had to come up with a mounting solution for it. How tall EXACTLY should a stand off be for the various pieces?

Most of this stuff was trial and error. Lots of errors. Just look at the pile of various attempts that will go in the trash after I post this:

One thing I discovered towards the end of the project was that I could cut the model and only print part of it. That was a real time saver. I could print the section I was trying to settle on and test it without waiting hours for the printer to finish the entire thing. I didn't read about using this capability anywhere on the web. Lots of folk talked about cutting the model, but didn't mention how it could be used to test a section of it. I guess most folk use 3D printers to make single piece items.

It's surprising how many little things creep up and have to be solved. The battery holder:

was initially a bit of a problem. I didn't want to mount it flat to the base plate because the mounting screws would go through the plastic, so I put in a couple of standoffs for the two screws that go through the holes in the middle of the assembly. Of course, that made it rock on the screws when I messed with the batteries. I solved that by putting in four more standoffs that kept it from moving.

Th circuit board with the electronics on it didn't have holes for mounting screws (oops).

So I had to work out special standoffs that could hold the board in place. Of course I didn't have washers that would fit the standoffs, so I just printed them as part of the base. Here's what the base wound up looking like after I solved these problems:

The battery holder has six standoffs two of them for actual mounting and the others to keep it steady. The standoffs for the PC board have a cutout for the board and I use little washers to hold it down securely:

The little dark spot in the center-left is a moth that was attracted to the heat and became part of one of the sensors. Note to self: close the printer door stupid.

I slid the lid up on one of the sensors so I could show off the construction of the assemblies:

If you zoom in on the picture you'll be able to see the mounting arrangement more closely. They were simple to install since they only take two #6 drywall screws and the entire device doesn't weigh much.

This project has been a lot of fun over the last couple of years. Yes, YEARS. And it isn't finished yet. I still want to use the sensors to replace the two house thermostats by taking the readings of each room and turning on heat, cool, or just fans to control the internal environment. I want to chart the outside temperature along with the rooms to see how it affects things as the day passes from season to season (notice, I only have two seasons here: nice and too-darn-hot). I may even create outdoor sensors to measure the wall temperature on some of the outside walls. That will prove the insulation effectiveness.

Who knows what I'll do with this in the future.


  1. Dave:
    I like the enclosure you have designed. Clean, simple and effective. Well done. Now you have a new hobby. 3D printing....I'm getting the urge to order a 3D printer.....
    Check out Duwayne's site He has been playing with project boxes that come in parts. You may find his adventures interesting....

  2. Hi Dave.
    i want build a wireless sensor network using raspberry pi and xbee for irrigation system.I want to have 5 xbee nodes. Each node consist of standalone xbee module with soil moisture sensor and a relay connected to it.At the coordinator side there is Raspberry with an xbee connected to it.

    My question is that is it possible that I can configure my xbees such that they all reads the moisture sensor every 1 second and sends reading to the coordinator.At the coordinator I want it to compared with the threshold values.If the value compared of a particular xbee is great than threshold then th xbee should send a command to that particular xbee ONLY to turn high on relay.I also want to save data in database in the raspberry pi.

    If this is is possible .Can you give me guideline of how to do it.

  3. Dave, Since I Followed you in your projects i have had some serious doubts.
    How have you done with the use of Arduino Hardware in your projects? Still work? Have not the noise, the climate, the work in them interfered and not been damaged?

    I have somre projects in process but i dont know if it is reliable to work with them in some enviroments and work 24hours / 7 days per year. I will apreciate your feedback

    1. The 'real' arduinos have never given me any problems with the heat or the cold. It doesn't get very cold here, but it does get really hot. I've had three of the clone boards fail from the heat and two fail only when it got down below 30F.

      Many of the projects were used for a year or two then recycled into some other project.

      Don't get them wet, they die and you have to be really careful drying them out. Insects can move in and make a mess, and their waste can eat the etching off the board. Lost one board to that problem.

      I've shown the enclosures I use outdoors and they seem to work fine if I check them from time to time and clean out the dust. Indoors I have a bunch of them in various enclosures and they work very reliably.

      Keep them away from caustic fumes. The fumes will eat the etchings off the boards. I haven't tried potting them yet; that should work fine if you need to.

      But, when you get the software right, these little things work for a very long time. You'll lose more power supplies than arduino boards.

  4. I have read your blog related to Room Temperature Sensor, but in these days, many people are using Smart Wireless Sensor WS1 to track an environment conditions, many people doing off road journey, doing gymnastic according to weather, many people always look or monitor the the data of outside from their homes, cause they are very conscious for their health.

    1. This is an obvious troll for the product you mention, but it does bring out a point. I don't want my data being held by a cloud service.

      There's way too many ways to misuse the data and then the company fails and the data disappears. I keep my own data.