project #7: MDEC64
64 points MIDI-to-Parallel decoder

This unit is available thru www.midiboutique.com

Description:

This project starts new line of projects:
MIDI receiving/decoding units. The main purpose is to drive pipe relays (valves) in classic pipe organs using MIDI interface. Using this unit different devices can be built also. For example, Light Music keyboard instrument can be easily assembled, based on mdec64. In this case, lamp drivers should be used for connecting lamps to the unit's outputs. Since the first purpose is driving organ pipes valves, examples for such drivers are shown below the unit schematic.

Schematic:
(click on schematic to get picture enlarged)

Used parts:

U1:PIC16F84.
U2:74LS138 decoder 3:8.
U3..U10:4099 addressable 8-bit latches.
Q1: Quartz resonator (crystal). Must be exactly 10MHz.
C1,C2: Capacitors 27pF each. Certain quartz resonators have these capacitors integrated. If you use such resonator, there is no need of C1 and C2.
R1: Resistor 2.2k.
R2: Resistor 330 Ohms.
R3: Resistor 220 Ohms.
SW1: 4-bit BIN switch for selecting MIDI channel.
X1: DIN 5 female connector. Used for connecting mdec64 to standard MIDI line.
D1: Opto-coupler PC-900 (Sharp) or 6N138 (Hewlett-Packard).

NOTE: The standard MIDI input device must have such opto-isolated input. This is an standard requirement for every MIDI input. Click here for more information about interfacing MIDI devices.

The power supply is standard regulated +5v. The pin #14 of U1, and pins #16 of U2..U10 are connected to Vcc (+5v wire), the pin #5 of U1, and the pins #8 of U2..U10 are connected to common (ground) wire. These pins are not shown on schematic.

NOTE: Using external power adaptors with output voltage more than 5v could damage the unit. As I know there are no 5v adaptors on the mass market. Making such adaptor is relatively simple work. You can click here to obtain such adaptor schematic. It is not required to be an electrician in order to make such adaptor but a basic knowledge about electrical safety is a must. I assume that reading this means that you are capable to build the schematic shown above, thus you are capable to build the adaptor yourself.

How MDEC64 looks:

Here is how the mdec64 prototype looks. Instead outputs there are LED's to indicate output status. The picture is taken during 'playing' the great Toccata And Fugue in D-minor by J.S.Bach.

And here is the production design of the unit (which you can purchase from me). It has two modifications.
The first one has TTL compatible outputs:

The second one (mdec64b) has output buffers, so it can drive loads at 30V/500mA max.:

Specifications:

• size 5x19cm (approx.2x7.5") standard mdec64
• size 6x19cm (approx.2.4x7.5") bufferized mdec64b
• opto-insulated MIDI-input
• MIDI channel selector
• built-in voltage regulator (input voltage AC/DC 6..12V)
• 64 parallel TTL compatible outputs for mdec64
• 64 parallel bufferized outputs for mdec64b, capable to drive loads at 30V/500mA
• two standard firmware modifications: low notes (note range 1..64) and high notes (note range 65..128), customer defined ranges are also available on request
• NoteOn, NoteOff, AllNotesOff MIDI messages on selected channel recognized, all other (including Realtime/SysEx) ignored
  

Paolo Airasca from Italy developed MIDI decoder based on mdec64 for controlling organ pipe valves (electromagnetic) via MIDI line. Here is how Paolo's PCB looks.

Vern Jones from USA made a version of mdec64 using integrated output drivers (see below).Here is his PCB.

Clicking on the picture, you can download file md64vj.zip containing whole information about Vern's version of mdec64, including:

• modified schematic diagram for using ULN2803 drivers;
• graphical original of PCB;
• components layout.

Vern's jewelry project MIDI Orchestra Bell Box using the MIDI decoder shown above is ready and working. More information about it can be found on Vern's site. There are placed also .mid (MIDI) and .rmj (Real Player, Real Jukebox) files so visitor is able to hear and compare synthesed and 'live' Bell Box performance. Here is a picture of Bell Box.
Great work, Vern!

Drivers:

Here are shown two examples of drivers for switching pipe organ valves or another types of relays/electromagnets. The maximal current that could be switched by these drivers is about 2 Amperes. For the most of such devices 0.8 - 1 A is enough.
These drawing are kindly provided/tested by Vern Jones. Here is a link to Vern's site.

The left side of drawing shows how to make valve drivers using power FET transistors (IRL520), and the right one shows using of power Darlington bipolar transistors(BD677).
NOTE: Both kinds of drivers can be connected directly to mdec64 outputs. No additional stages are needed.

Another driver solution is using integrated drivers. Vern Jones used ULN2801/2/3/4/5 for his design (shown above). These devices include 8 Darlington transistors with protective diodes on each. They are capable to switch up to 500mA. Here is datasheet (pdf format).

Ordering:

Details about how to order pre-programmed chip or ready made unit can be found here.
The package includes mdec64 unit and User Manual with fully documented schematic and MIDI Implementation Table.
Two models: non-buffered (mdec64) and buffered (mdec64b) are currently available. Custom note range is supported, including non-continuous note ranges.