Archive for May, 2010

Apple 1 Registry Started

Friday, May 21st, 2010

This page is intended to provide as much information as possible about known original Apple 1 Computers. If you have information to share about an original, and it’s not on this page, send me an email.

Blown Transformer

Tuesday, May 11th, 2010

Just a heads up folks. One Mimeo 1 builder had a P-8667 transformer fail. The windings must have shorted out. Good thing that the Mimeo was being monitored and could be shut down before any serious damage to the Mimeo or building in which it was operated, occurred. Anyway, the result was a smokey, smelly transformer that no longer works, but no damage to the motherboard or anything else. I’ll put up a picture of the transformer, when I get a chance. It is unclear what triggered this failure, but it probably was a manufacturing problem with the transformer.

As I point out in the build manual, do not operate your Mimeo, unless someone is present to take immediate action in case of component failure. These old designs don’t have all the safety features of modern consumer electronics. Some of the components supplied with the kit are over 30 years old, so unexpected, early failure is always a possibility that should be accounted for.

One more little tidbit I picked up from the owner of this unit. Mounting the two transformers at right angles to each other, should help reduce stray coupling between them. I don’t know how much of an effect this has on performance, but I figured I’d share the tip.

ACI update

Saturday, May 1st, 2010

I’m making headway on the Apple Cassette Interface clone layout.

ACI developmental CAD view

Here are my current plans.

1) Finish the layout – I’m estimating that will take a couple of weeks. This will be laid out to the same replication standard as the A1 motherboard.
2) Find a current production cassette recorder that works well with the ACI.
3) Come up with pricing for the kit – right now I’m estimating between $75 and $100. I want to make it $75, the cost of an original ACI in 1976, but that low price point might be difficult to attain.
4) Build an interest list of potential purchasers. This time around I don’t plan on ordering any parts or the PCB until I get about X number of folks on the interest list. I’ll determine what X is when I figure out the cost of kit. This number will probably be between 12 and 25 individuals.
5) When the interest list reaches critical size, but before finally ordering parts and the PCB, I may well ask for pre-order payment to confirm that this is financially viable. A lot of folks will express interest and get on the interest list, but back out for one reason or another when asked to actually part with their money.

PS/2 Keyboard Interface Design Decisions

Saturday, May 1st, 2010

Someone sent me an email asking if I could have created a PS/2 adapter that was reconfigurable in software to work with either an Apple 1 or Apple II with no hardware jumpering. I started to compose a long answer and before sending it, realized that this would be a good blog entry. So here it is.

The AVR to DIP wiring mechanism was the most difficult part of the design process, for the PS/2 keyboard adapter.

First of all I couldn’t do a software switch between the A1 and A2 pin outs without some external power switching circuitry, as the power and ground connections are different. For example, minus 12V on the Apple 1 is connected to the same pin as a data bit on an A2 keyboard.

I wanted to support S-100 and other systems with possibly different pin outs, with a standard ribbon cable. I thought about creating a user interface with the serial port to allow tweaking configuration, but decided it was too much work and could cause too much confusion, if configured wrong.

I was also concerned about increasing potential for bugs. The code for the PS/2 keyboard is pretty complex, as it is. Besides doing the bit banging to move stuff over the wire, you have to keep track of key states. Some single key state changes result in 3 bytes being transferred to the adapter. You don’t really know what is going on with the keyboard until all three bytes are recieved. When you finally decide that you have a character for the host, you then have to map a generic key code into an ASCII equivalent. A depressed shift, control or other key affects the translation.

I actually laid out at least 3 variations of this board over the past couple of years. First version was a single sided PCB and A2 specific. This one can be seen at the bottom of my keyboard adapter web page. The next version was A2 specific, but you could cut existing traces and add jumper wires for other systems. Here is a CAD image of this version.

A2 version with option to cut and rewire

The Data bits are optimized for the A2 connection, not ease of wiring. Notice that I also reversed connector ends between this version and the final version. This was to make the ribbon cable connection between an A1 and this adapter more straight forward. I think that in most cases with an A1, the adapter will be to the left of the motherboard. With the original configuration this would require twisting the ribbon cable to connect correctly.

Finally, I decided I needed to create the most generic version possible, because of the desire to support systems which could have any sort of pin out. I considered making it default to A1, and then allow cutting traces and adding wires to adapt to other systems, but decided that cutting traces was destructive and not very elegant for non-A1 applications.

Once I decided that I didn’t want to force non-A1 folks to cut traces, I rearranged the pads and pin out to make hookup as straight forward as possible. I think in this regard, I succeeded. When I wired my first boards, I found it much easier to do, than when I built a wire wrap A2 keyboard to A1 converter using two wire wrap sockets. I also figured that it was going to be sold as a kit. A little extra work on the kit builder’s part, really wasn’t necessarily a bad thing. 🙂

I guess this long winded blog indicates how much I thought about the problem. The optimum design would to make a different board for each application, but it would not have been economically feasible.

I’m very happy with the result and have been exclusively using a PS/2 keyboard with my A1. The long cord and keyboard layout is much more user friendly than using an A2 plus keyboard with ribbon cable connection.