The basic idea for this ring was to take a piece of a aluminum to make the ring out of, design it to fit the PCB and peltier, and create a heatsink that mounts on the other side of the peltier unit. Originally I had planed to make this a single finger ring but somewhere along the way my brain had fallen for a 2 finger design; It was much more practical, and surprisingly the PCB I made was the perfect size to fit across two fingers, leaving the heat sink on the side. Oddly enough I have a few ring sizing tools hanging around (thanks to my Grandpa having lots of random tools) so I measured the two fingers it would go on and away I went with a design.
Here is the design I came up with. Overly fancy for the sake of not actually machining yet.
I managed to find some time at my school to use the CNC Mill. I fired up EdgeCam and created a G-code file. I started with a block of aluminum and milled away the ring from the top, ending up with this.
One thing you don’t realize with double finger rings is how much harder it is to remove from your hand when it doesn’t fit! I ended up somehow making the ring finger hole(the bigger one) too small for my finger and I had already removed it from the machine. I decided to just work the metal by hand to up-size the hole until it fit. It wasn’t fun testing it out, each time thinking it would be stuck, as I don’t like the feeling. Finally it got to the point where it fit perfectly to my hand and I was happy.
I decided to not mill away the two contours that make it skinnier on the bottom. My think was: 1) it didn’t feel uncomfortable(actually looked better too) and 2) It would retain more heat from my body having more surface area.
After Several weeks of waiting for my PCB(which cost me $4 for 3 of them shipped by the way), they finally came in the mail. This meant I could finish the ring machining. I was holding off so I could use the actual dimensions of the PCB for when I machined the metal. The original slot idea was off the table as my school’s Mill doesn’t have the proper slotting tool so I decided to just do a step. I first populated one of the boards with the components so I would know if there were any issues.
Here is a comparison to the old testing board and the new board for mounting on the ring.
I just used the CNC by hand jogging to do the cutting. It was faster than putting in some G-code and its fun to do some hand machining every so often.
You can see the small step I left for any vias or solder that made its way though, to prevent shorting on the ring.
It fit pretty well inside. As for making it a permanent fixture. I will probably use some type of glue, it seems to stay in pretty well on its own, so nothing too hard will be needed.
This is the completed ring with the peltier module hooked up and a rigged up heat sink. In the future I will be making a custom heat sink, and figuring how I’m going to secure it, but for now a hacked up computer sink and a rubber band seems to be doing alright. I’m already implementing some design changes in the first revision; one being the removal of the super-cap. It doesn’t technically need it, but I will replace it with a smaller regular capacitor. It sticks up too far for me to be comfortable with it.
So here is the finished ring. In my room its a little warm so under a fan I can get the LED to glow just from the heat of my hand. To me this was the goal of the ring, and the fact that it worked at all is amazing. I am going to be making a few revisions to this PCB design(already have). The first will be instead of having the LED just faintly lit(my transistor circuit is not working right) I’m going to be implementing a Miller Engine circuit. Instead of using a motor like what is normally done, I will replace it with an LED. Using the 1382 IC when the circuit sees 2V, which will be given by Vgood pin on the Linear 3108 IC then it will trip the LED transistor. I believe this will allow the system to charge up fully and then fire the LED making it blink instead of faintly lit. I’m hoping this is the case.
update: Here is a short teaser vid of the ring lighting up outside!