Greetings! In this project I’ll show you how to build a light kit for your 3d printed or resin cast Thermal Detonator. There are a lot of ways to get where this kit goes so the first thing to do is set some parameters:
- I wanted it to run on a coin cell battery
- I wanted to be able to reprogram the light sequence
- I wanted the spoon on the top to slide open to activate the red LED and the blinking sequence
- I wanted it to be reproducible and affordable
In order to meet the first requirement I had to select components that ran happily on 3.3 volts, which eliminated a lot of arduino solutions. To meet the second requirement eliminated just using a timer or transistor logic gates. The last requirement didn’t play into the “brain” discussion, but presented some engineering challenges later. After heading to my parts bin I realized the PICAXE system would be perfect for this. PICAXE chips can hold a large number of input/outputs, run at 3.3 volts, cost about 83 cents each, and are easy to work with.
- 1x 08M2 PICAXE Microcontroller
- 3x 3mm Yellow LED’s 2.1 forward voltage
- 1x 3mm Red LED 2.1 forward voltage
- 1x 10ohm resistor
- 4x 120ohm resistors
- 1x 100nf ceramic capacitor
- 1x roller switch
- 1x coin cell battery holder
- 1x 8 leg IC socket
Step 1: Breadboarding
With any electronics project the first step is to build the darn thing so it can be toyed with. I like to use the Fritzing program with the PICAXE tools to layout the circuit. For my first prototype I used simple LED’s, an 8 leg PICAXE controller, and some spare parts I had laying around.
From there I needed to program the PICAXE itself, because I wanted to replicate the sequence from RoTJ and didn’t want to sit down and do all the timing myself I looked if anyone had already done the code, and they had! I used this code initially:
Step 2: Prototyping
After I had the code working on the breadboard it was time to start building the components. To save space I replaced the long legs on the LED’s with inline resistors and sealed them with some heat shrink tubing:
Here is where I made my first mistake, I should have put the chip in an IC socket, on the same side as the battery and all of the other components coming out of the other side of the breadboard, the way I did it meant I could not easily reprogram the chip and made fitting it into the detonator later a challenge:
From here I was able to cram it all in the top and start building my mechanical piece for the spoon:
Step 3: The Mechanical Switch
In order to get the spoon to slide over the roller switch to activate it I had to get creative. I needed the switch to be able to move front to back, but not twist side to side. I also needed the spoon to sit and slide smoothly over the top of the sphere, without falling out. In order to accomplish this I carved a channel into the top of the detonator, put a long keel on the bottom of the spoon, and attached a paddle to it to hold it in place.
First, I carved the keel out of a spare piece of 6mm sintra I had laying around, and the paddle out of 3mm sintra.
I attached the keel to the spoon with RedHot blue glue for PVC, which works *amazing* with sintra. From here I was able to measure and carve out the channel on the top of the detonator with my rotary tool based on the shape from the keel:
After the channel was carved, I put the keel through the channel, and secured it by using more RedHot to attach the paddle to the keel:
And that’s that! The lighting should all be working, and you just need to finish assembling & painting the thermal detonator like normal.