Before we begin the fun, we need to get the ugly part out of the way. We (Ed Holzknecht and Jim Combs) DO NOT give or imply any warranty, or guarantee, for the safety, accuracy, and or usefulness of this project. This means that if you build this and your machine becomes a smoke generator, sorry, but you knew the risk when you started. If you have questions about this circuit, we will attempt to answer them, but again, we cannot guarantee any answers for accuracy.
Remember, if you build this project, you do so at your own risk!
The first part of this file and the accompanying DPaint schematic is "author unknown"; we would love to give credit where credit is due, but we don't know who to give it to. All we know is that the circuit works. We have added comments at the end of the next section to possibly help people that build the circuit and then have some problems accessing the drive. Also, my co-conspirator in this endeavor , Jim Combs, (actually, he did the hard part - he built it, all I did was cut wire) has some construction notes at the end of this file.
REVISED VERSION (AUTHOR UNKNOWN! - Please pat yourself on the back!)
In order to be able to use any IBM compatible DSDD 5-1/4 disk drive with the "mount" command, a special latching and recognition circuit is necessary. The schematic enclosed is drawn with DPaint in hi res with 1 bit plane. The 23 pin connector plugs into the back of df1:. As you are probably aware, this is a difficult to get connector. However, a 25 pin connector can be cut down to fit. Just remember to renumber pins 13-23 appropriately. The 34 pin connector is a standard card edge connector universally used to interface with 5-1/4 inch drives.
Be sure the drive you use has the drive # select jumper in the drive 0 (the lowest number available) position, as the Amiga does the selecting, assuming all drives are number 0. Pins #9,20, and 21 are the drive select lines, and are rotated in the Amiga boxes, so that line 21 out of Amy selects df1:, and line 21 out of df1: selects df2:. Actually, out of Amy, line 21 selects df1:, line 9 selects df2: and line 20 selects df3:. All on the 23 pin connector, of course.
In addition to the circuit depicted, you will need a 12 volt and 5 volt power supply appropriate to the disk drive. The last I looked, Radio Shack had two different combined supplies priced at around $5.
Any construction technique should work. Mine is wire wrapped, but worked well on a breadboard as well. Don't forget RF shielding if you or your neighbors have trouble. This is probably not a beginner project since an improperly wired connector could damage the Amiga, or the 5-1/4 drive. Anyone with a little experience should have no difficulty, however.
This circuitry works with Transformer, as well, if you can get a dealer to sell it to you cheaply without the bundled drive.
ADDENDUM TO THE ABOVE 8/19/87
This circuit works very well indeed! I have a IBM Tandon internal drive interfaced to the Amiga and assigned DF2: and have not had any problems at all. This works well with Transformer software as well.
There are a couple of things I would like to point out that I found out through trial and error. First, when you first boot up, you MUST NOT have a disk in the 5.25 drive, or the Amiga will poll it and assign it as df2: automatically, and consider it as a 3.5in external 80 track drive! Leave the door open and then after booting (make sure you have"mount df2:" in your startup-sequence) put a disk in the drive and do a "cd df2:". The Amiga will then access the drive and see it as a 5.25 drive formatted for 440K. Also, be sure to use the "Diskchange" command EVERY time you change the disk, or you can expect an occasional visit from the Guru!
Ed Holzknecht 8/19/87
I built this board using a Radio Shack Perforated Circuit board and wire-wrap sockets for the two ICs. This makes for easy positioning and allows some freedom for modification. Use wire-wrap pins for cable connections to allow you to completely assemble the board and double check all connections, preferably with an ohmmeter. If you are careful, you should have no problems, as this is a straight forward point to point wiring job. Radio Shack also sells the necessary 34 pin connector, and the ribbon cable you will need. Just remember that you cannot have a total cable length of more than one meter (about 3 feet) starting from the plug in the amiga, and ending at the 34 pin connector. When you are wiring this thing, avoid sharp angles, they act like antennas, and will emit rf big time. Just keep your wiring neat, and as short as possible.
