Blog Posts

Harmonicade: Arcade Button Synth

The Harmonicade is an impressive synth made of over 200 arcade buttons, a Teensy 3.6 and a lot of 3D printing.

The person behind KOOP Instruments wanted to learn to make music, but the traditional piano layout didn’t suit him. So, he started making his own range of musical midi devices, which are now all immaculately written up and shared over on the KOOP Instruments site.

The Harmonicade is a multi-channel MIDI keyboard using arcade push-buttons in a Wicki-Hayden style button layout, a musical keyboard layout based on hexagons. It uses over 200 arcade buttons feeding into a single Teensy 3.6 via two sets of DB25 connectors – an ingenious solution to his wiring problem!

As with all the other KOOP Instruments releases, the Harmonicade has been impeccably documented, including step-by-step build instructions with detailed wiring instructions, 3D modelling files, and helpfully commented code.

You can also read a write up of the Harmonicade on the Hackaday blog.


Quadruped Walking Robot

Scaraman, a PJRC forum user, has shared their progress on a quadruped walking robot project that uses a Teensy 4.

Scaraman wants to make a walking robot that is controlled by a neural network. To achieve that aim, they first had to figure out how to make an ordinary walking robot, the results of which can be seen by watching the video above or by reading Scaraman’s detailed post on the PJRC forum.

Scaraman explains that they chose Teensy 4 to base this first version of the robot on as it has the computing power to run real time neural networks in future versions of the quadruped. One of the interesting design features of this project are the legs and feet. Scaraman has chosen to use a five bar parallel (also known as a five bar Scara arm) design with an extension. The feet also have sensors in them to provide information to the Teensy about foot placement.

For more videos of the robot in action, including it traversing across an obstacle course and climbing up a staircase made of books, check out Scaraman’s YouTube channel.

Teensy 4.1 Released

Teensy 4.1 is now available with access more I/O and memory expansion.

Teensy 4.1 features a 10/100 Mbit Ethernet PHY.

The Ethernet port also has IEEE1588 precision packet timestamping.

Fast Ethernet opens up possibility for low latency & high bandwidth Artnet LED projects, streaming audio, open sound control and other Ethernet-based protocols that were difficult to accomplish with a traditional SPI-based Ethernet shield.  Traditionally use of Ethernet in a project has involved a choice of single board computers with high bandwidth Ethernet using systems not designed for low latency tasks, versus microcontrollers designed for real-time tasks but with slow Ethernet or lacking performance to handle Ethernet’s speed.  Teensy 4.1 with a Cortex-M7 processor at 600 MHz opens up the possibility to use the high bandwidth and low latency of Ethernet on a microcontroller designed for real-time tasks.

Teensy 4.1 includes a USB host port, supporting 480 Mbit/sec high speed USB.  While Teensy 4.0 has those USB host data signals on surface mount pads, Teensy 4.1 adds the hot-plugging power management needed to simply connect a USB host cable and be able to plug in a USB device.  Or a USB hubs can be used to connect many USB devices.

USB devices are supported by the USBHost_t36 library, which is installed into the Arduino IDE automatically by the Teensyduino installer.

Another feature technically present on Teensy 4.0, but difficult to use, is native SDIO for fast data transfer to a SD card.  Teensy 4.1 includes the SD socket, so you can easily use a micro SD card with the card’s native SDIO protocol rather than slow SPI access.

Teensy 4.1 also includes locations to solder additional memory chips.  The larger space is meant for a QSPI flash memory and the smaller space is intended for a 8MB PSRAM chip.

The IMXRT1062 microcontroller on Teensy 4.0 and 4.1 has 1MB of RAM built in.  For many real-time control projects, the internal RAM is plenty.  But some projects can greatly benefit from the added memory.  Frame buffers for high resolution TFT displays are the most common use, allowing advanced graphics rendering.  Large memory is also very useful for special audio effects like advanced reverb, buffering fast incoming data before logging to a SD card, and for emulation of retro computer systems like classic arcade games.


These extra memory chips have a dedicated QSPI bus, which is independent from Teensy 4.1’s main program memory.  When a flash memory chip added for storage of files or other data, this dedicated bus means it does not interfere with normal program memory access.  This is especially valuable while writing data or erasing sectors in the extra flash memory.  For real time projects controller motors, synthesizing or processing real-time audio, communicating high speed data or other tasks requiring low latency, flash writing can be done to the extra flash chip without blocking access to the normal program memory.

Teensy 4.1’s larger form factor also bring more I/O pins, and makes the difficult-to-access bottom pads from Teensy 4.0 very easy to access, breadboard-friendly pins.  The new I/O pins bring an 8th serial port, more analog inputs and PWM outputs, and access to 16 contiguous native port pins, useful for projects needing fast parallel I/O.

Not every project requires so much I/O or extra memory.  Teensy 4.0 fills those needs.  But when you do need more I/O, more memory, fast Ethernet, or connecting USB devices or fast SD card access, the larger Teensy 4.1 brings this extra I/O capability to a platform designed for real-time use with fast 600 MHz M7 performance.

Wristpass: a Pebble Watch Password Manager

Jeffrey Turley has made a wearable encrypted password manager using a Teensy 3.2, a Pebble watch and KeePass.

Jeffrey Turley’s Wristpass prototype connects to any computer, emulating a keyboard to input your password. The passwords themselves are secured on your phone by KeePass, which keeps them encrypted until you need to access them. Watch this Teensy powered password manager in action in the video above, or read more about this project on Turley’s Hackster page, where you can also see a couple of his other Pebble watch projects.

Scrobby: a Solar Panel Cleaning Robot

Stefan Hamminga has made Scrobby, a robot designed for cleaning solar panels autonomously.

Scrobby was built by Stefan Hamminga using a Teensy 3, a Bluetooth LE module, six ultrasonic sensors and two internal motor driven spools. It is powered by its own solar panel. When Scrobby’s sensors detect rain, it moves across the solar panel surface, scrubbing it clean. When rain stops falling, Scrobby goes back to a special resting platform, meaning that the body of the robot doesn’t block any valuable sunlight. You can find build logs and explanations of Hamminga’s mechanical design decisions over on Scrobby’s project page.

MicroDexed and MDAE Piano Synthesis

Holger (C0d3man on the forum) posted details of some excellent synth projects that gets a powerful Dexed FM synth plugin running on Teensy.

Holger combined a custom PCB with a Teensy and the PJRC Audio board to make a neat synth module that supports MIDI, both DIN and USB. Holger also ported multi platform, multi format plugin synth Dexed to this module.

Holger has published details of three separate audio projects that use this system, the Teensy MIDI Audio, MicroDexed and Micro MDAE Piano, all of which are Open Source Software and Hardware. You can listen to a recording of some of the sounds from MicroDexed and Micro MDAE Piano on Holger’s website. You can also read more details about these projects on the PJRC forum and the Zynthian forum.

IKEA LACK Table Lamp Clock

Christoph has published a number of cool projects over at His latest hack, for the Hackaday Tell Time, is turning an IKEA LACK table into a ceiling-mounted robotic LED clock.

Christoph used an IKEA LACK table, twelve small hanging lamps, twelve servos, a Teensy microcontroller and an ESP 32 to make this project. Each lamp can be moved up and down by its own individual servo, stopping at one of five positions: 0% (fully down), 25%, 50%, 75% and 100% (fully up). The position of the lamps tell the time, for example at 01:15 lamp one would be at 75%, lamp two 25% and the rest at 0%. You can find build logs and code for this project over on the website.

The other winners of the Hackaday Tell Time contest are also really worth checking out. The PJRC blog has previously featured the overall winner, this beautiful and technically impressive ferrofluid clock by a talented team of students from University of Oslo.

Schapiro Audio Skillet

Shapiro Audio have released the Skillet, a pro-audio MIDI controller built with two Teensy++ 2.0 boards. The Skillet is designed to be used with Avid Pro Tools.

The Skillet was designed to to control plugins in your DAW in a less fiddly, more interesting way. The device’s joysticks can control up to six parameters, and you can map them to any automatable plugin in Pro Tools. It also has dual touch-sensitive 100mm motorized faders and a nice-looking touchscreen menu system.

The Skillet uses two Teensy++ 2.0s: one to provide USB-MIDI output and convert all the control inputs into MIDI-based protocols, and the other to drive the touchscreen. If this sounds like something that would improve your audio production set up, you can get one on the Schapiro Audio website.