Re-programmable 8×8 LED Matrix

An ATTiny85-based LED Matrix “backpack” PCB design.

Back of PCB

Easily re-programmable, low-cost BOM, simple construction, and tons of fun! This small PCB fits to the back of an LED Matrix and drives animations.

Front of PCB

At the heart of the design is an atTiny85 microcontroller. It holds the animation and library to drive the matrix. In addition, a MAX7219 LED driver is used to interface with the matrix.

Matrix when off

Animations can be uploaded over USB and programmed in the Arduino IDE.

Want to build it yourself!? EAGLE schematic and board layout can be found below.


  • 1x ATTiny85 Microcontroller (SMD)
  • 1x MAX7219CNG (THT)
  • 1x 8*8 LED Matrix (I used the LTH1388BSR)
  • 2x 3.6v Zener Diode (for USB Bus)
  • 1x MicroUSB Connector (SMD)
  • 1x 6mm Tact-switch (SMD)
  • 2x 68 ohm resistor (0805)
  • 1x 30k ohm resistor (0805)
  • 1x 1.5k ohm resistor (0805)


DIY Wireless Speakers – Part 1: Transmitter

Welcome to my DIY wireless speakers tutorial. We will be building/modifying an FM receiver and FM transmitter to turn them into wireless speakers. First we’ll build the FM transmitter.

To do this, we’ll modify a car FM transmitter (available on eBay). These are a popular solution for cars without AUX connectors, you can connect an iPod’s headphone jack to the FM transmitter, and hear your audio over the radio.

To use this device, we’ll have to make a few modifications. First, I removed the 5V power supply circuitry, which wasn’t necessary anymore. Then I soldered an old USB cable to the output of the 5V supply. Now we can power the circuit over USB instead of car power.

To get the audio into the mix, I replaced the 3.5mm female port with the end of an old pair of headphones, so that we could plug it into the back of, say, a TV.

For aesthetics, I built the circuit into a black box, and cut out holes for the cables.

Now we have an FM transmitter, next we need the receiver. Stay tuned for part 2!

Useless Machine

A simple desk toy that switches itself off. While the idea is non-unique, the design and 3D print files are.

The lid and arm are meant to be 3D printed and fitted to a box of dimensions 7x7x14cm.

The two switches (main switch and reverse stop switch) are soldered to a PCB which is mounted to the enclosure by the nuts included with the main switch. Note: the main switch shown in the photos is red, switches available for purchase are blue. There is no difference.

The main driving arm is mounted to a 9G servo, and designed to hit the main switch at one extension, and hit the reverse stop switch at the other.


3D CAD File


  • Main switch – available from
  • Reversing switch – available from
  • Continuous rotation servo
  • PCB – order online or etch at home
  • Arm – 3D print online or locally
  • Lid – 3D print (as above) or make a simple lid from wood or a material of your choice (I used foam board)
  • Case – build a simple box out of your material of choice (I used foam board) to the dimensions specified above.