| MIDI Kit
$19.00 
MIDI Cable
Microcontroller
|
This project shows you how the hardware of a MIDI interface works and goes through some simple examples to show how the controller can be used in MIDI systems. First we will start by explaining the details of the hardware interface. Then we will look at the MIDI protocol and see how simple it is to write custom software for this MIDI controller. The MIDI Hardware Interface
6N137 Optoisolator
Sending a Signal The microcontroller sends signals through the MIDI port by controlling the voltage at its pin 3. The current is provided by the 5 volts (Vcc) connected to pin 4 of the MIDI Out port. When the MIDI Out port is connected to a MIDI In port of another system the following circuit is created.
You should be able to build the MIDI controller from the first schematic at the top of the page. Use the MIDI connector with the ground wire for the MIDI out port. If you need help with the electronics, read some of the material at http://www.iguanalabs/mbktut . You should end up with something that looks like the picture below.
You can also add an LED going from 5 volts to Pin 2 of the 2051, in series with a 510 ohm resistor, to have a visual indication when there is activity on the MIDI In Port. You can do the same for Pin 3 to see activity on the MIDI Out Port. Using MIDI - The Software Before we get into the actual software for the controller, we will look at a few simple MIDI commands. The first is a Note On command. This tells the receiving system to play a particular note. Then we send a Note Off command to tell the system to stop playing the note. The commands are made up of a series of bytes. The Note On command is 3 bytes. It looks like 9x yy zz x is the channel number. There are 16 possible channels (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F). yy is the note number and can be anything between 00 and 7F (0 and 127 in decimal values). zz is the attack velocity and can be anything between 01 and 7F (an attack velocity of 00 makes the Note On command into a Note Off command). The Note Off command is about the same. It is 8x yy zz. The values are the same as before except zz is the release velocity. For our first example we will make the controller play some notes. The software is midi1.asm. You only need to connect a a MIDI cable from the MIDI out port of the circuit to the MIDI IN port of a keyboard. Study the documentation in the software file to learn more about how the software works. The basic process of compiling an assembly language program and loading it into the microcontroller was covered in the first microcontroller project. Compile the program and download it to the 2051. Make sure the power is off to the circuit you have built. Then move the 2051 to the circuit. Turn on the power to the breadboard. The second example monitors inputs on the MIDI IN port of the controller. When a Note Off command is detected, the controller sends out a Note On and Note Off command for the same note. This creates a sort of echo effect. The software is midi2.asm. You can order the parts for this project. It includes:
1 - 24 MHz Crystal 2 - 33 pF Capacitors 1 - 10 uF Capacitor 2 - 510 ohm Resistors 2 - 8.2k ohm Resistors 3 - 220 ohm Resistors 1 - 6N137 1 - Diode 2 - Green LEDs 2 - MIDI connectors soldered with wires for breadboard. 1 - 220 uF Capacitor 1 - LM7805 5 Volt regulator 1 - DC Power Jack soldered with wires for breadboard Jumper Wires Catalog
-- Support -- Privacy
Policy -- About Us
|
