Wireless Charger

September 6, 2020

One of the things that I have regretted as I've gotten older is not taking more time to learn from my dad by working through projects. He is a man of many talents and much knowledge and I would be lucky to learn even a little from him. Knowing I had a few days to off from work to use and a long weekend coming up, I planned this small project for us to work on together. 

With everything going on I am spending more time working remotely I have been considering upgrading my desk. My current desk is great and has been with me for something like 15 years, but it just doesn't have enough width for my monitors. This means that I've been watching many videos on desk builds and dream setups. One thing I found interesting was this video by Snazzy Labs. He mentions some drawbacks of just putting a premade Qi charger under the desk, mainly adding additional distance between the coils and the device being charged. Using his eBay link, I decided to pick up a few bare coils and see if I could make something out of it.

Wireless power transmission is not new a new idea. The theory has been around since the 1800s. It just took until recently for it to be small enough and efficient enough for it to be used in portable electronics. First, let's look at how induction stoves work. Alternating current electricity (the type found in your wall outlets) is passed into a power coil, which looks like a flattened spiral of copper wire, and the electrons begin to move. As the current passes through the coil a magnetic field is generated. When a second coil is placed over this power coil, usually in the form of a pot or pan made specifically for induction stoves, the coil in the bottom reacts to the magnetic field and the electrons start to move in the new coil. When the currents movement meets resistance, heat is formed. Obviously this is ideal if you are trying to cook, but we don't wouldn't want our phones to get that hot! Instead, the current from the phone's coil is passed into a power rectifier. This takes the alternating current (AC) and converts it into direct current (DC) which your phone can then use to charge. This may sound complicated, but that's okay, you can buy transmission coils already made, and some newer devices come with receiver coils already installed.

I know a lot of my projects start with Fusion360, but that's because it's such a great piece of software once you've had some practice. I was able to make my drawing with rough measurements, and then by editing the parameters once I had my digital calipers handy I could dial in the design without redrawing everything. This took some work because the panel-mount micro USB extension I have from Adafruit needed to plug into the controller board and then be mounted to the outside of the case. To keep things as simple as possible, we decided to go with a three-piece assembly, consisting of a plain top and bottom and then a middle layer which would have a large portion in the center removed to contain the charger. A lot of people will route out the bottom of their desks to create a space. This approach is effective, but rarely very appealing.

Having my plan finalized, I exported the base sketch from Fusion360 as a DXF file and imported that into Adobe Illustrator. Once I had the import scale set I was able to print two patterns. Looking through my dad's stock of wood we settled on a piece of curly maple flooring. After cutting off the tongue and groove on the table saw and removing the textured bottom and thinning the piece down to the desired size on the planer we had a good blank to work with. Using the ever-useful glue stick, I applied my patterns to the blank for cutting with the drill press and bandsaw. 

Using a Forstner bit on the drill press I was able to remove a majority of the interior material and also get some pretty sweet rounded corners. Having that done, the bandsaw helped remove the rest of the interior waste and cut the parts where the panel-mount extension would attach. Back on the drill press, we drilled some holes for the USB mount. With the bottom glued it was a good time to test the fit of all of the components. Fortunately, our measurements were correct and everything was ready for final assembly. After lots of time sanding and a few coats of paste wax the units were finished and looking pretty nice if I do say so myself. 

To wrap this project up there are naturally a few things that could have gone smoother. The paper template worked so well, I wish I had used it when locating the holes for the USB plug. The holes ended up being a bit too wide which pulled the pieces in, throwing the whole thing out of square. The hole for the USB plug could have been smaller but would have required more drilling. The coils come with an indicator LED, but this design seals it away. Not everything is negative. It had been a while since I used a drill press and bandsaw. I also got a chance to work with a belt sander. They are not difficult to use, but it never hurts to have a little practice!