Revisiting One Of My First Projects – Now With More LEDs! (“Block M” Pin Update #1)

As far back as I can remember, I’ve been a fan of Michigan Football. Whenever I would go to games, I’d get all decked out in Maize and Blue. But at some point late in high school, I decided that wearing a bright yellow hoodie, sweat pants, gloves, hat, shoes and socks just wasn’t quite enough. Sure, I was the most fashionable guy around, but surely there had to be a way for me to show my school spirit even more. So I went down to my basement workshop, printed out some iron-on circuit boards, mixed up some chemicals, got my Radioshack soldering iron hot and made this:

Why yes, that ‘soldermask’ is blue spray paint

A blue “Block M” pin, with blinking yellow LEDs. Sure, it’s got some shortcomings and oversights (current limiting resistors? We don’t need no stinkin’ current limiting resistors), but I was in high school, so I’ll give it a solid C for effort. Let’s take a quick look at what we’ve got on the board:

  • Single sided PCB (with two wire jumpers)
  • 12mm battery
  • 11x 5MM yellow LEDs
  • ATTiny85 8-pin microcontroller
  • Power switch
  • Safety pin (not only does the hot glue keep it in place, it also prevents it from shorting the power switch, wow!)

“But wait!”, I hear you saying. “There are 11 LEDs, and your microchip only has 8 pins, how are you controlling all the LEDs separately?” Oh, I already thought of that and it’s simple… I’m not. I simply created 5 groups of LEDs and controlled each group with an IO pin. That leaves two pins for power and the other pin (reset) is left floating — quite literally, the copper pad came off when I drilled the hole, so it’s not even soldered. As far as the blinking goes, it had several different patterns and used the non-volatile EEPROM to switch to the next pattern each time you turned it off and on. All things considered, I’m amazed that this circuit worked as well as it did; the battery lasted long enough to blink for multiple games before needing to be changed and even now, nearly 10 years later, it still works.

A couple of years after making this, when I was in college, I discovered the miracle of $10 PCBs and decided I should order a couple of boards to make them more “professional”. I added a second battery holder in parallel to double the run-time and submitted my Eagle board file to iTead. Unfortunately, at that point, my experience in PCB fabrication was primarily limited to etching boards at home, so I ended up with white labels and part names all over the front of the board. Regardless, I was just excited to have something manufactured, so I didn’t particularly care.

Technically an improvement, I guess?

This one has actual soldermask on it, a surface finish that won’t oxidize, and twice the battery capacity! Good work, Freshman-Ben. The improvements stop there, though. Same 5 groups of LEDs, same code, and a more visually-cluttered front.

For the next several years I wore these occasionally, but mostly just let them gather dust and thought of them fondly as a fun little side project I made when I was younger. In early 2018, I was on a circuit board streak that had me ordering new PCBs every month or so for a handful of projects and I thought to myself “You’ve learned a ton since you built these, why not give it another go and see what you can come up with?”

My list of must haves included:

  • No unnecessary silkscreen on the front
  • Surface mount components
  • Visual flare with either ENIG or yellow silkscreen, if possible
  • More “badge-friendly” design
  • Individually addressable LEDs

I searched the web for a PCB manufacturer that would make small quantities of blue soldermask with yellow silkscreen and stumbled across AllPCB. I’ll talk more about them when I write a post comparing all the manufacturers I’ve used, but they were willing to use the unique color combination I wanted for a very reasonable price, not to mention they included free DHL shipping. I got to work on a new design and a couple of hours later placed the order. I’ll admit that I was a bit hasty on the layout because I misread the AllPCB website and thought the free-shipping was a temporary sale. In my haste, I forgot to put my signature and design date on the back of the PCB. Darn.

Five days later (seriously, PCB manufacturing is unbelievable these days), the PCBs showed up and I ripped the box open:

Wowee. Would you look at that yellow silkscreen!

Whoops. This was originally supposed to include pictures of the assembled pin, a code overview, power optimization and a video, but I’ve rambled far too long already. I’ll end this post here and have another one with all those exciting details soon.

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