‘Starburst One’: Single Alphanumeric LED Display with ATtiny461A Embedded on the Back, Powered by USB

Wow this thing looks amazing! That’s a single ATtiny461A (in SOP20 package) mounted on a custom PCB that mounts to the rear of a single alphanumeric display. The text displayed – in this case, ‘I LOVE YOU’ – scrolls through one letter at a time, and is powered by USB for 5V standard. The board files and code are provided here – and this prototype was built on an Othermill with hand soldering, making this a fairly accessible – if medium difficulty – project (and it looks great!).

This is a little weekend project I made with parts I had lying around: an Atmel ATtiny461A drives an LTP-587G alphanumeric LED display. The only additional part needed is a 68 ohm current limiting resistor. Power is +5V from a USB wall adapter.

AVR-GCC source and KiCad design files are included. This is my first KiCad project: I’ve used gEDA for everything in the past, but development seems to be stagnating and it’s a pain to use on a Mac.

The PCB is the same size as the display itself. It is single-sided and requires one jumper wire to be placed. (indicated by the single trace on the back copper layer in the PCB layout.) I made one with an Othermill, using 1/32″ and 1/64″ flat endmills. Hand soldering is straightforward, but the ATtiny’s large SOP-20 package is just a bit too big for my footprint, so I had to squeeze the legs in a little bit beforehand.

The firmware displays a hard-coded message one character at a time, with short blanking periods between each so that consecutive identical characters can be distinguished. All segments are multiplexed: only one is ever lit at a time. However, because the ATtiny461A only has 15 usable I/Os (PB7 must be used for /RESET in order to use in-system programming) I tied the top two segments together. There is no apparent effect on brightness.

The code is pretty much the simplest thing that could work. No interrupts, no fancy animations, no user input. I will most likely leave this project in its current state and build a second version using an MCU capable of driving all segments, as well a brighter/larger LED module.

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