MIDI to Parallel Unit
By John Wale
My recent posting about my MIDI interface system has created some interest, so here are some further details about the system.
The idea behind designing a small MIDI to parallel interface was that most users of such a system would be hobbyists like me, who had built their own mechanical instruments (an organ in my case) with a few dozen notes and didn't need all the complexity of the commercially available units to make their instruments MIDI compatible.
My MIDI to parallel converter (MTP-1 as I've called it) uses an 8-bit microcontroller to do all the real-time processing. To keep the cost down, most of the work is done by the software, which was written in assembly language to make it as fast and efficient as possible.
The MTP-1 receives standard MIDI data and responds to note on, note off and active sensing commands. Running status is supported. The channel number to receive on (range 1-16) is set by four dip switches which are read when the unit is powered up.
Many small organs do not have a chromatic scale, so the system can be set up at the time of production to map any MIDI note number(s) to any of the outputs. This means that no outputs are wasted by being assigned to notes that don't exist on the instrument, and the ability to map several MIDI note numbers to one output allows notes outside the normal range of the instrument to be played an octave up or down.
I use some home-written PC software to read in the mapping data from a table and then output the assembly code with the mapping built in. This is then assembled and programmed into the microcontroller in the conventional manner.
If the system were to be used in a larger instrument, a number of MTP-1 units can be 'slaved' together to cover the full range. Individual units can be set to different MIDI channels if required within a grouped system.
Each MTP-1 has 32 outputs, each output being capable of directly driving inductive or resistive loads, such as solenoids or lamps. The outputs are 'pull down' and can sink up to 0.5 Amps with a maximum supply of 35 Volts.
The unit is intended to be fitted as a permanent installation witihin an instrument and is built onto a single printed circuit board measuring 50 by 220 millimetres. The board has a standard 5-pin DIN socket for the MIDI input and a row of 36 screw terminals which provide connection for the 32 outputs, the power supply and chaining between units in a large system. There is also an LED which is lit when power is on and flashes on and off in the event of a MIDI communications error.
Power for the unit is derived from the power to the output devices which can be in the range 7 to 35 Volts dc.
At the moment, I am building the first 'pre-production' prototypes which should be ready in a week or two. If I were to build units to order, the delivery would probably be on a 1 month basis.
As I put in my previous posting, I think I can produce these units for about 42 pounds (UK) each, including configuration programming.
Anyone interested in this system is welcome to contact me.
John Wale.
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(Message sent Tue 29 Oct 1996, 09:22:54 GMT, from time zone GMT.) |
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