SwitchGear MidiBox by Blu3Dawg ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ All About Midi ~~~~~~~~~~~~~~ Midi is a simple interface that allows your computer, in this case an Amiga, to talk to a keyboard. MIDI utilizes dangerous switching voltages whis are hard for a computer to handle. THe swing between on and off is -12 to 12VDC. This was most likely implemented since older computers had to worry more about interpretation and Interference from radio sources. Midi, as it stands, is a fairly crude, one-way communication line with individual inputs and outputs. Because it doesnt follow single line bidirectional protocols a certain interface must be used to help more modern computers to use the technology. With this simple box you can use midi for around $20 USD (including cabling). My Happy Box ~~~~~~~~~~~~ I was fortunate to find schematics for this circuit on the aminet in an old hardware pack... unfortunately his parts lists were unavailable in the US and Canada. In addition, the schematics were not standard and the english instructions were incomprehensible (no offence). I have included VERY clear schematics and a nice foil pattern should you want to make yourself a printed circuit board. The Parts list is as follows: D1, D2 - 1N4148 Signal Diode R1, R4 - 220 ohm Resistors R2 - 4.7 K Resistor R3 - 10 K Resistor all resistors 1/4 watt @ 5% tolerance R5 - 1.2 K resistor Q1 - NTE123A Low Loss VHF NPN Transistor U1 - NTE3041 NPN optoisolator 2 - Midi Jacks (Din-5 Female) for the I/O to the Keyboard 1 - DB-25 Serial connector (DB-25 Female all pins connected) 2 - MIDI patch cables I used a 55 x 84 mm Enclosure for the PCB and connectors (its a tight fit but it's beautiful :) ) The Construction of the PCB ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Now this is a very simple circuit to make. if you feel like printing a PCB read this section for complete details. Now with pixels it is very difficult to gauge the scaling of your printer. I have picked a standard of 600 DPI to print at. Printing in 600 DPI will give you a very accurate PCB and all components will simply slide into place without troubles. Should your printer have difficulty at such a resolution try scaling the image with a paint program. I have tested the PCB and it works without a hitch. Now, print out "MidiboxPat.iff", included in the archive. this contains 3 seperate images a component side of the board, a foil side of the board, and a building diagram. these are all accurate and work. If you are printing a PCB, copy the "foil side" diagram to a piece of photocopier-safe transparency and follow the normal etching process. Once your PCB is etched and drilled begin to solder the components to the board ( I find starting with diodes is best; then resistors next and sensitive components such as transistors and IC's last.) You will notice a discrepency, there is no trace on the PCB for the connection of pins 4 and 5 of the DB25 connector. The reason for this is I just bridged the two pins at the connector instead of bringing wires down to the PCB. so it should look like this: DB-25 (rear view) 1 solder bridge 13 . . . .L. . . . . . . . . . . . . . . . . . . . . 14 25 all the connectors are numbered accordingly to the diagram so connection of the connectors is a snap. now you are ready to mount the PCB in an enclosure. The Enclosure ~~~~~~~~~~~~~ To design a nice enclosure I recommend getting a nice, prefabricated, square plastic box with a lid. the measurements as mentioned before are 55 mm by 84 mm. for my project I used a Radio Shack experimentor box. If using a metal box, be VERY cautious with spacing the PCB. make sure NO leads touch the box and connect pin 1 of the serial port to the chassis to provide better protection from interference. All you need to do is drill a couple of holes into one end and make a rectangular cut in the cabinet to mount the connectors. The BOTTOM of the DB-25 connector should be 6mm off of the table in order to align with the amigas serial port. drill pilot holes for the screws co you dont deform your cabinet. Use self-tapping screws for the approprite size of your particular connectors around a 4/40 screw should suffice. once the circuit is securely in place connect your midi patch cables and power up your miggy :) Enjoy. Testing ~~~~~~~ This circuit has been tested on an Amiga 1200 and an Amiga 500. I assume it will work on all standard amigas. However, I am unsure if it will operate on the A1000 and A1500 so for those who want one for those system, you're out of luck, sorry. If you like to look up equivalencies perhaps you could fabricate your own. but dont come crying to me if it doesnt work. :) Legal ~~~~~ I do not warrant this project in any way shape or form. I assume no responsibility for damages caused by my interface. it works for me but others may have less experience. if you do not feel you can manage this project DO NOT ATTEMPT TO MAKE IT. USE AT YOUR OWN RISK. you have been warned. if you are having problems you may contact me at the adresses below. Blu3Dawg the hopeful ~~~~~~~~~~~~~~~~~~~~ If you have found my project stimulating and useful perhaps you could compliment me by sending a few dollars or pounds or deutch marks or francs or lira or yen or whatever :) you know I can always hope. Adresses ~~~~~~~~ Should you feel a burning desire to contact me, if you have problems or if you would like to send me money you can reach me at E-Mail: wi511@victoria.tc.ca IRC: nick Blu3Dawg on #Amigascne Home: Richard Hoar #73-1732 Newton Street Victoria, B.C. CANADA V8R-2R2 --AMiGA RoX 4 EvEr---------^--- - - -