SAM: now with lights!

Everyone knows that go-karts go faster when they have cool lights.

My controller and batteries all sit on a 1/8″ sheet of polycarb which is transparent, so right under the controller was a good place to put the lights. I got two strips of RGB LEDs. This was my first time playing with them and they are awesome! All the LEDs are in parallel, and all the colors have a common anode (+ terminal). So to turn a particular color on, you just pull the corresponding pin to ground.

I wanted to use an Arduino to control the lights and make them fade through different colors, but the Arduino cannot supply the necessary current. Instead, the Arduino switches a transistor that then switches the LEDs, which are hooked up to a separate supply. Instead of transistors, I ended up using a Darlington transistor chip (I used a ULN2003AN). Darlington transistors are when a transistor drives a transistor which then drives your load. My friends more fluent in electronics say that this drives the load “harder”, and has to do with the multiplied gain of the transistors. Yea…someday I’ll actually understand what that means…

I also wanted to learn pcb layout and etching, hence the comically simple schematic. One highly misleading element of this schematic is the capacitor from battery +26V to V1 of the 7812. Its actually a thermister, I was just lazy and wanted the right hole spacing. The thermister is to guard against the possibility of this board shorting the  main battery.

After this I bumbled through the process of converting this to a board. Below is the result printed on the back photo paper which releases toner easily, I guess. The toner was transferred to a freshly sanded pcb blank with an iron. A sharpie is used for any touch up.

Next, it etched away in a tub of ferric chloride for about 15 mins.

Then I drilled out the holes. This wasn’t that precise, but if you slightly oversize the holes, it works out.

I put a heatsink on the 7812 just in case. Below is everything right before plugging into the battery. The code for the Arduino is pretty simple. But its even simpler to briefly search the internet, and copy paste.

The underglow while it is one the ground is nice. I plan to play around more with the colors, too.