A business card-sized love detector in a 3D-printed package.

2024 Business Card Challenge: Who Do You Love?

When you hand your new acquaintance one of your cards, there’s a chance you might feel an instant connection. But what if you could know almost instantly whether they felt the same way? With the Dr. Love card, you can erase all doubt.

As you may have guessed, the card uses Galvanic Skin Response. That’s the fancy term for the fact that your skin’s electrical properties change when you sweat, making it easier for electricity to pass through it. There are two sensors, one on each short end of the card where you would both naturally touch it upon exchange. Except this time, if you want to test the waters, you’ll have to wait 10-15 seconds while Dr. Love assesses your chemistry.

The doctor in this case is an RP2040-LCD-0.96, which is what it sounds like — a Raspberry Pi Pico with a small LCD attached. For the sensors, [Un Kyu Lee] simply used 8mm-wide strips of nickel. If you want to build your own, be sure to check out the build guide and watch the video after the break for a demonstration of Dr. Love in action.

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2024 Business Card Challenge: Tiny MIDI Keyboard

The progress for electronics over the past seven decades or so has always trended towards smaller or more dense components. Moore’s Law is the famous example of this, but even when we’re not talking about transistors specifically, technology tends to get either more power efficient or smaller. This MIDI keyboard, for example, is small enough that it will fit in the space of a standard business card which would have been an impossibility with the technology available when MIDI first became standardized, and as such is the latest entry in our Business Card Challenge.

[Alana] originally built this tiny musical instrument to always have a keyboard available on the go, and the amount of features packed into this tiny board definitely fits that design goal. It has 18 keys with additional buttons to change the octave and volume, and has additional support for sustain and modulation as well. The buttons and diodes are multiplexed in order to fit the IO for the microcontroller, a Seeed Studio Xiao SAMD21, and it also meets the USB-C standards so it will work with essentially any modern computer available including most smartphones and tablets so [Alana] can easily interface it with Finale, a popular music notation software.

Additionally, the project’s GitHub page has much more detail including all of the Arduino code needed to build a MIDI controller like this one. This particular project has perhaps the best size-to-usefulness ratio we’ve seen for compact MIDI controllers thanks to the USB-C and extremely small components used on the PCB, although the Starshine controller or these high-resolution controllers are also worth investigating if you’re in the market for compact MIDI devices like this one.

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A stack of PCB business cards that can play Snake on an 8x8 LED matrix.

2024 Business Card Challenge: Snakes On A Business Card

Once [Lambert the Maker] saw the Arduboy, he knew the thing was ripe for remixing into a business card with an 8×8 LED matrix instead of an OLED screen. [Lambert] already has a PCB business card for work, but it looks like it doesn’t do anything. So this Snake-playing card is for their personal information.

The brains of this operation is an STM32F0, which required a bit of finesse when it came to programming the LEDs. According to the datasheet, the max current through a given GPIO pin is 30 mA. The LEDs are running at 20 mA through the limiting resistor, so the code only turns on one LED at a time and makes sure the previous one is off first. The whole screen is updated every 125 ms, and persistence of vision takes care of making the animation look right.

In the short videos after the break, you’ll see a preview followed by brief videos on versions one and two. The prototype was built in 2020, when the board house only offered green PCBs with their assembly service. Fast forward to 2024, when the board house is now offering colors other than green.

Version two is actually thinner than a credit card, and features tiny buttons instead of cap-sense pads for input. [Lambert] also added a floating ADC pin that acts as a random number generator, placing the apple in a new location every time the game is powered on.

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A PCB business card with a built-in 4x4 tic-tac-toe game on the back.

2024 Business Card Contest: A Game For Two

If you want to make a good first impression on someone, it seems like the longer you can keep them talking, the better. After all, if they want to keep talking, that’s a pretty good sign that even if you don’t become business partners, you might end up friends. What better way to make an acquaintance than over a friendly game of tic-tac-toe?

This one will probably take them by surprise, being a 4×4 matrix rather than the usual 3×3, but that just makes it more interesting. The front of the card has all the usual details, and the back is a field of LEDs and micro switches. Instead of using X and O, [Edison Science Corner] is using colors — green for player one, and red for player two. Since playing requires the taking of turns, the microcontroller lights up green and red with alternating single-button presses.

Speaking of, the brains of this operation is an ATMega328P-AU programmed with Arduino. If you’d like to make your own tic-tac-toe business card, the schematic, BOM, and code are all available. Be sure to check out the build and demo video after the break.

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The 2024 Business Card Challenge Starts Now

If you want to make circuits for a living, what better way to impress a future employer than to hand them a piece of your work to take home? But even if you’re just hacking for fun, you can still turn your calling into your calling card.

We are inviting you to submit your coolest business card hacks for us all to admire, and the top three entries will win a $150 DigiKey shopping spree.  If your work can fit on a business card, create a project page for it over on Hackaday.io and enter it in the 2024 Business Card Contest. Share your tiny hacks!

To enter, create a project for your hacked business card over at Hackaday IO, and then enter it into the 2024 Business Card Challenge by selecting the pulldown on the left. It’s that easy.

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