tindie badge bodge

A project log for weekend novelty projects

minimal advanced planning. built from stuff i already have around the shop. typically not very useful. generally completed in one weekend.

zakqwyzakqwy 12/08/2017 at 15:382 Comments

Yup, my #Tindie Blinky LED Badge now has extra LEDs.

The badge runs on an ATtiny84A; I chose this chip because I had a few lying around and it's got sufficient I/O to drive each LED on a dedicated I/O line. Also, the 0.5mm pitch of the QFN nicely matches an 0804 resistor network; probably not necessary (as the coin cell has a high internal resistance) but they make soldering magnet wire a bit easier. The image above shows the badge hooked up to the AVR Listener for ISP flashing; this required a bit of wrangling with polyamide tape as the temporary programming leads like to fall off if physically disturbed.

The t84 is held down using a resistor lead tacked to its ground pad. Otherwise, most of the connections go to LEDs via 220-ohm resistor networks where possible, or through discrete 0402 resistors where not. I did include a bypass capacitor; it's a bit tough to see in the loupe picture above, as it is tombstoned just above the chip and connected directly to the power rail. Wiring power up this way means the power switch still works!

Each LED is connected to its own I/O port. A matrix configuration would have allowed me to use a different microcontroller and save a few solder joints, but the common-cathode scheme means a simple grounded wire loop can support all of the LEDs via one of the original LED pads. The anodes are individually connected using 34 AWG polyurethane insulated magnet wire; it's thin enough that all five leads fit through the LED (+) pad.

Code is simple enough to not include here -- a timer interrupt to generate a tick, a helper function to update the LEDs, and an integer to store their value that increments with every loop. And it likely won't change, as I conformally coated the back of the board to protect the components a bit. We'll see how long the badge survives as the eyes are rather delicate.


Jarrett wrote 05/14/2018 at 18:51 point

Well what the hell Zach. That's not a thing that should be possible

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morgan wrote 05/15/2018 at 03:04 point

why. can't. we. like. comments! (or embed youtube videos...)

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