The most important 3D print (She said yes!)

The following post is a short decription of how I made an engagement ring for my girlfriend. First I’ll show you the build process

Now, the details:
I figured that Making an engagement ring should contain something from ‘me’. That meant that making the ring myself was essential. I went through different ideas and I found a guy who made a ring from titanium and installed an induction coil along with LEDs. (http://www.kokes.net/projectlonghaul/projectlonghaul.htm) The main problem with a project lige this is that I don’t have the tools nor the knowledge to pull it off. I knew however that I wanted to have electronics installed in the ring.

It would be fair to note at this point that My girfriend is hoem earlier than me. keeping a project like this a secret is not easy. I however, managed to keep the real reason behind my new 3d printer a secret (the old one just wasn’t capable of making the model). The design phase was relatively straightforward. The ring is temporary – My girlfriend is working as a dental hygienist and can’t wear a ring at work. Other solutions exist and i will explain later.

Electronics
I planned on having a self-contained unit so some sort of power was needed. I looked for super capacitors but in the end I couldn’t find anything that was small enough. Co-incidently I met my dad and saw him change batteries on his hearing aids. There was my solution! I got his remaining batteries (thanks dad!) and knew that I had my power source.

I had some PIC10F320 MCU’s in SOT-23-6 package. Those things are TINY! The reason I chose that specific MCU is that is has a PWM module (actually it has two) so wiring it to a single LED should be easy.

Next up was to actually find a LED. SMD LEDs come in many different sizes. I found a 0603 size with reverse pads, meaning that the actual LED is on the bottom. At least that’s what I think I used because I got 3 different kinds with different brightness. Okay – Solder time:

On the picture above the complete circuit is shown. The wires are headphone wires. they were the only ones I could find that was flexible enough while still being insulated. The grid on the paper is 5 by 5 mm (or you could use the ‘normal’ LED in the background as reference – it’s a regular 5mm one)
What you can’t see is that the LED is pulsing very slowly. It had a nice effect like a slow heartbeat!

The install in the ring was fairly uneventful but There was some trickery involving not getting the thing to short-circuit while stuffing it all in.

As you can see the batteries will just fit. The wires had to be soldered to the batteries itself – I know it’s bad practice but that was the only option I had.

the last thing I did was to seal the ring with some hot glue. The light is visible through and it keeps the components in place.

One problem
I knew that the batteries only have 100mAh of energy in them. What I didn’t knew was that the recommended current draw is about 4-5mA. When my LEd is on it draws (or try to draw) 20mA. ouch. I could see the pulse becomming dimmer and dimmer with each ‘breath’ because the battery couldn’t keep up.

I better hurry and get on my knees!

EDIT:

She said yes 🙂