Dovetailed Arduino Humidity Sensor

We live in Central Texas and throughout most of the year we get massive swings in the humidity in our shop. As woodworkers, this can be tough on certain projects so we built an Arduino-powered 'Shop Sensor' to give us a visually appealing way to see how the humidity is changing! It's made from Walnut and has dovetail joinery and as the humidity changes the color of the lighting shifts across the color spectrum. It also has an LCD screen in one of the eyes that displays the temperature in the room.

One of our favorite things is combining fine woodworking with technology and this was a really fun project where we did just that.

This project has some woodworking, some electronics and some 3D printing.

Why does humidity matter in woodworking?

The simple answer is that wood reacts to changes in the moisture content in the air by expanding and contracting. Even after it's completely dry and even with finish on it, almost all wood continues to "move". This can pull apart joints, cause drawers not to fit, and other nasty things. To learn more about this phenomenon, we recommend a google search!

COMPONENTS USED:

• Arduino Uno
• Adafruit Neopixel Ring
• Adafruit 1.44" LCD Screen
• DHT22 Humidity Sensor
• 4x AA Battery Pack
• Mini-SD Card

TOOLS USED:

• 3D Printer
• Router
• Utility Knife
• File
• Clamps
• Soldering Iron
• Solder
• Hot Glue Gun
• Tape Measure
• Pencil
• Chisel
• Marking Gauge
• Planer (Not Required)
• Jointer (Not Required)
• Bandsaw (Not Required)
• Tablesaw (Not Required)
• Rotary Tool / Dremel (Not Required)
• Drill Press (Not Required)

MATERIALS:

• Walnut (Wooden Case)
• Frostic Acrylic (Light Diffuser)
• PLA (3D Printed Skull Logo)
• Wood Glue
• Super Glue
• Hot Glue
• Blue Painters Tape
• Double-sided Scotch Tape
• Shellac

To build the case we used Walnut which is dark brown/grey hardwood. Why Walnut? It's easy to work with, we had some, and it generally looks awesome...making it a great choice for this! Do you need to use Walnut? No! You can use any species of wood for this.

The milling process for the Walnut was first to flatten and straighten it on the jointer, resaw some smaller 3/8" thick pieces on the bandsaw, and then plane them to final thickness using the thickness planer.

Don't have your own milling tools? No worries! You can purchase lumber that is already at the thickness you want to use and skip this first part!

With the Walnut milled flat, straight, and to our final thickness, we ripped it to the final width on the tablesaw and then cross-cut it to final length.

The result of this process was four pieces that were all perfectly flat, straight, and exactly the size we wanted. Since we're cutting dovetails, having perfectly sized pieces will make it much easier later on. If the pieces aren't the same size or they're not square, the dovetails won't fit together well.

As shown in the pictures and video, a dovetail is a joint where two pieces come together by means of a dovetail-shaped tenon, known as the "tail", that fits into a mortise in between two "pins". It's a challenging and fun joint to create. Also they look AWESOME.

You don't need to use dovetails for this...but...challenge yourself...try it!

We started by measuring out the size and location of our pins and tails on the boards. We then use a jig on the table-saw to make our cuts.

(The jig we're using is from Fine Woodworking magazine and it's really easy to make. There's a fantastic video on YouTube showing you how to make it. You can find it by searching "Table saw dovetails" on YouTube.)

The first jig has the table-saw blade angled to about 10 degrees to cut the tails and then the second jig has the blade back to 90 degrees but angles the workpiece to the same angle as before and clears out the waste. We use a flat top rip blade for this and if we do it right, this should fit right off the table-saw.....

Well... They didn't. :)

We had to make some adjustments using a chisel and some clever use of scrap pieces to hide the problems, but they came out great in the end.

You can see more detail on this part in the video in Step 1.

The case has an open back and the front sits nicely inside a 1/8" deep "stopped" groove. To cut the groove, we used a router.

It's called a "stopped" groove because it doesn't go all the way from one end to the other. It starts part way in and ends right before you get to the edge. (See pictures.)

In this case, if the groove had gone all the way to the end it would have poked through the dovetails and you'd see it clearly. Since we didn't want that, we used a stopped groove.

The top was made from some 1/4 thick walnut and ripped and cross cut to size. From there we did our first dry fit and everything was looking good!

The idea for the front of the case was to have a cut out in the shape of our logo and have the light shine through it from behind. At first we tried to rout the skull logo from a piece of wood but...it was a disaster. So, we decided to 3D print the skull and paint it white which turned out great!

We also 3D printed an outline that is slightly bigger than the skull, used double sided tape to secure it to the front, and then used a sharp knife to trace the outline into the wood. With the sharp and defined "knife line", we then used the router to clear out the waste in the middle. We used a 1/16" straight router bit and went incredibly slow to rout out up to the line.

For final detail, we used a small hand file and clean away any tool marks or missed spots.

From there, we glued up the wood case and once the glue was dry we chamfered the dovetails and edges of the case with a chisel and a handplane.

Behind the skull was going to be a piece of frosted white plastic. This was here to "diffuse" the light behind it to help it spread out more and look better. We found a small sheet of the plastic at the big box store and cut out a piece to fit in our case.

We first did a test to ensure it was going to look good and everything was awesome! We weren't 100% sure this plastic would diffuse the light properly but happily it did.

Next we used some double-sided tape to temporarily hold the 3D print of the skull in place so we could get the positioning of the left eye. This was going to be replaced with an LCD screen so we needed to remove the plastic. We used a marker to mark out the area to be removed and then cleared away the waste by drilling out most of it on the drill press and then cleaning up the line with a sanding drum and rotary tool.

Before gluing in the frosted plastic, we finished the case with Shellac. We used 3 coats and then polished it with steel wool and paste wax.

With the case finished inside and out, we could use super glue to attach the plastic from inside.

The components we needed to install were the battery pack (4x AA), the humidity and temp sensor, the LCD screen, the light ring and of course the Arduino Uno. We spent a lot of time "prototyping" to see how this would all work and once we things working we had to figure out how to fit it all in the wooden case. We had done some of this in parallel so that when we built the case we knew how big to make it.

We used blue tape to rough in the position of the components and ensure they'd fit and then used hot glue to hold in the LCD screen and the Arduino's plastic case on the side. The plastic case/holder is helpful because we can pull the Arduino in and out if necessary.

The Neopixel LED ring was hot glued to the battery pack, the humidity sensor was hot glued on the top left of the wooden case, and then a small breadboard was hot glued to the bottom of the wooden case that would serve as a power junction.

The only soldering we had to do was for the power, data input, and ground wires on the Neopixel ring. We also used a heat gun and some heat shrink tubing to help manage the wires and hold them in place. With the soldering done we hot glued the battery pack onto the wooden case which resulted in the light ring being exactly centered and right where it needed to be to diffuse the light properly. (If it's too close to the plastic it doesn't spread out as much as you lose some of the effect.)

The battery pack has a small on/off switch which is how we toggle the power for the project, so we made sure it was accessible. The pack also opens towards the back so we could replace the batteries when necessary.

From there all of the components were ready for final wiring.

The programming of the Arduino was relatively easy. It checks the temperature and displays it on the screen. It also checks the humidity and adjusts the color of the LEDs based on how humid it is. The most humid is when it's purple, which means 95%+ humidity. It's purple way too often...but that's central Texas for you!

As Jaimie mentions in the video, this project took WAY LONGER than we thought when we started it. But, it really did come out great. It now lives in our shop and lets us know at a glance how humid it is in the shop.

For some reason we LOVE mixing fine woodworking and technology. It's just so much fun.

Our favorite thing about this cross-discipline project is that it reminds us that when you mix creativity and a passion for making awesome stuff, there really is no limit to what you can invent and make.

Now...go make something!

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