I’ve finished the hardware part of my Teensy 2.0 based iPad MIDI interface project.
Getting it to fit in the smallest possible Hammond 1551 box was a challenge. I rebuilt the circuit no less than three times before getting it to fit in the the 1551H enclosure. The 8-pin opto-isolator used on the proto was replaced with a 6-pin Sharp PC900 to save space.
Update 1: Supply current is about 35mA. Not sure if this can be reduced below the 20mA limit.
Update 2: I’ve managed to get the operating current down to about 22mA without changing hardware. A simple code change – to take advantage of the idle mode when waiting for events – saved a few milliamps. About 10mA savings comes from setting the clock to 8MHz instead of the default 16MHz.
According to the Teensy documentation, another 7mA of savings is possible using a 3.3V linear regulator IC that can be installed on the back side of the board. That should drop the operating current well below the 20mA limit.
See below for more pics and schematic.
Here’s a fun project I started about two months ago, and finished this weekend. It’s a DMC Ground Control (GC), modified with Teensy++2.0 controller, which turns it into a powerful USB expander footswitch for use with my Axe-FX Ultra and MFC-101.
Here’s a short video showing the various features:
Here’s a simple hardware project that would be a good first-time project for anyone interested in creating their own USB MIDI device.
For this project I used a small and inexpensive USB-based microcontroller board called the Teensy 2.0. This tiny board is packed with features: 25 I/O pins, 12 analog inputs, 7 PWM outputs, 16MHz processor, USB 2.0 full-speed/low-speed, UART, SPI, and I2C.
Teensy 2.0 development board
I used the free Arduino software development platform for this project. The Arduino language is similar to C, so anyone familiar with C will feel right at home. The company that makes the Teensy provides an extension to Arduino called TeensyDuino, which adds support for the USB 2.0 port. Making a USB device could not be easier.