Archive for June, 2010

To retrace this road…

Wednesday, June 30th, 2010

this blog thread will take you back in time to 1987. I was single, about 30 years old, and had a good job as a software engineer. I had plenty of time, money and passion for competition and adventure.

I lived in Florida and had been racing Prindle catamaran sailboats as a hobby for over five years.

My friend Phil flying a hull on the Atlantic Ocean

My group of sailing friends were also full of adventure. Sailing and racing 300 pound, 16 foot long boats with a bunch of sail area on the Atlantic Ocean was not for scaredy cats. It was a physically and mentally demanding sport. We pushed those little boats to the limits and frequently beyond. Damaged and broken boats were not uncommon. Bodily damage was mostly limited to sunburn, cuts and bruises. The number of near misses were countless.

At the time, I felt that winning sailboat races was the toughest thing I had tried to succeed at. Maybe to this day, there is nothing I’ve tried harder and longer at mastering.

Sherry and Sue show off matching bruises after a particularly tough day on the water - we were sure that some visitors to the beach thought that we beat our girlfriends because of all the bruises

Eventually some of the group that I enjoyed racing with, started drifting away from sailing. Marriages came and babies followed and priorities changed. New people were slow to enter the sport as the brand new sport of windsurfing was much less expensive to get into and took far less effort to participate in. The people that remained in the sport were investing in bigger, more expensive boats that required crews. I preferred racing my boats single-handed. As the group slowly drifted apart, I started losing interest in catamaran racing, and found myself spending more and more time on my bicycle.

Datanetics Web Page Started

Sunday, June 27th, 2010

Mostly just have schematics which I spent the last week drawing and a few notes on key switches and the encoder part.

Datanetics Keyboard Update

Saturday, June 19th, 2010

Current State of Datanetics Layout

I’ve got all connections made, except for the connections from the blank keys to the matrix on the upper left side of the keyboard. From here I may take a break and make a schematic, since I’m not aware of any in existence for this keyboard.

I still have holes to drill 🙂 and plenty of fine tuning to do. This layout will match a Rev B board. There is a mistake in the original layout of this board which requires a couple of of cuts and and a jumper. I will probably leave the mistake in place.

The pinout of the edge connector is:

Front (from inside of board moving toward edge when facing front of board, left to right)
B6 (B is data bit)
Reset key pin 1
Reset key pin 2
Output enable (this is an input to the keyboard, but is pulled up on the board to +5 volts)
STROBE (output)

back side of keyboard (from edge of board moving inward when facing back of board) (Right to left)
blank keyswitch 2-2
blank keyswitch 2-1
blank keyswitch 1-2
blank keyswitch 1-1
blank keyswitch 3-2
blank keyswitch 3-1
blank keyswitch 4-2
blank keyswitch 4-1
+5 Volts

Now it’s time to go for a bike ride.

Coming Soon…

Wednesday, June 16th, 2010

An illustrated blog retracing the low tech road I travelled for three weeks in the summer of 1988.

New Project

Friday, June 11th, 2010


Quick update – while waiting for the panasonic cassette recorder to arrive, I’ve started work on a new project.

This is going to be a Datanetics Keyboard PCB. This was the keyboard that was most commonly used with Apple 1 computers. There were several revisions made. I’m likely to layout the rev D, since it used most of the same keycap set as early Apple IIs. However, I have access to an actual, original rev B, and may decide that I can do a more faithful replication of that version.

Note that some of the important parts for this keyboard can be very hard to find. The MM5740/AAE keyboard encoder is a very difficult IC to find. Furthermore, the ones you do find, sometimes do not work reliably. Randomly repeating characters after warm up is the symptom of this problem. It would be possible to program a micro controller to accomplish the same function and mount it on a plug in daughter card. However, I think I have enough MM5740’s to satisfy my own needs, so I’ll leave that to someone else. As far as I know, Datanetics key switches and key caps can only be sourced from early Apple II plus computers. The early Apple II/plus keyboards used the same keyswitch and the same style key caps. In fact those keyboards were made for Apple by Datanetics. There are also some metals stiffeners that will be have to be fabricated in order to complete the project.

Because of the difficulty of finding parts, my plans are to only sell bare PCBs, leaving it up to the prospective keyboard builder to find the parts for his build. In addition, I will ask for pre-payment and only order enough PCBs to fill pre-paid orders. I’ll be accepting pre-orders when I feel that the layout is ready for production. The order will be placed when I have enough pre-orders to justify making a build.

Apple Cassette Interface (ACI) update

Thursday, June 3rd, 2010

I’m still working on the ACI layout, but I have some more things to do.

I want to make sure that I can make operation more reliable before I make a batch of cards for consumption by hobbyists. Besides the capacitor change, I want to find a cassette recorder that works better than the vintage Radio Shack model that I’ve been using. Even with the capacitor change, operation is not the most reliable in the world with this recorder. The recorder I’m waiting to try is the Apple specified cassette tecorder. This is a Panasonic RQ-2102, which much to my surprise is still in production. This recorder was recommended and used by Apple back in the 1970s. I have a new one on order, but it’s on back order and not due to arrive for several more weeks. Used ones are often available on eBay, but I’m looking for a new one, since belts on cassette recorders tend to stretch and slip with age.

The ACI layout is largely complete, with only rounding off of the corners of the traces and final design checks remaining to be done. Though I did the initial layout in a couple of hours, I’ve spent a lot more time than I expected fine tuning the replication of the details of the original. I think that because the board is small, finer fidelity to the original is required to ensure that I capture the right look and feel on this board

New Apple 2 Rev 0 Revelations

Wednesday, June 2nd, 2010

I did a comparison of the hidden traces on my rev 0 replica with the fantastic image of the front bare Apple II rev 0 PCB, that I just received from Stanford University. I found that all of these “hidden” routes were precisely the same as the actual rev 0, except for two.

  • First was a trace I connected, that didn’t exist on the rev 0, but was later added on the rev 1. This is the pull up on pin 12 of the 74LS74 at B-10.

    missing pullup on rev 0

    The image on the left, is the original. Note that this missing trace is actually an undocumented bug in the rev 0. The trace connects the D input of a flip flop with a pull up. Without the D input to the flip flop being pulled up, it is left in a “floating state”, That means that when a clock edge is seen on the flip flop, that either a positive or negative level will be clocked in, depending on exactly where the input is floating at. Usually this will be a positive level, since 74LS input logic tends to float high, but it’s far from guaranteed. This flip-flop is used to indicate to the computer when a character is pressed on the keyboard. This floating input could cause the computer to miss keystrokes. I don’t remember this being a problem on my original rev 0, but the possibility is there.

    When laying out the replica PCB, I ended up cutting up a socket on a later rev board in order to determine the route of this trace, not realizing that it wasn’t even present on the rev 0. The poor photocopy in the “RED BOOK” occasionally wasn’t good enough for me to solve a puzzle, and I had to resort to this sort of tactic, from time to time. In this case it failed me. Looking at the image now clearly shows that the trace wasn’t present, but there are other places on the photocopy where present traces are barely visible. For some reason traces that ran vertically often show up poorly in this photocopy.

    74LS74 photocopy area

    It you have one of my replica’s and want to experience authentic behavior, lift pin 12 of the flip-flop out of the socket (or you can bend it under so the change doesn’t look obvious). You probably will not notice any difference in behavior. You could also cut the trace, but I would recommend that you leave well enough alone and run it as is, with the input properly pulled up.

  • The second difference is also interesting. This difference resolves a misconception I had about the implementation of the fabled USER1 bus line on the Apple expansion slots. The USER1 jumper is documented incorrectly in the Apple II reference manual. The vias that need to be connected to enable USER1 are partly obscured by the ear of the Slot 7 connector, so adding this jumper, would have to be done from the back of the board. In Apple’s “Hobby/Prototyping Board” document it says “The function of this line will be described in a later document.” USER1 must not have been used by any I/O cards since it was reused on the IIe as 65C02 sync and changed again on the IIGS to M2 SEL.

    The routing of trace in question is partly hidden by the ear of the slot 7 connector. I connected pin 39 of the peripheral bus, USER1, from the peripheral bus to the wrong via. This via directly connects to the enable on H12. USER1 should have connected to another via, that is not connected to anything else. The user was supposed to add a jumper between two vias to make this connection.

    If you have one of my rev 0 replica’s I would do nothing. I have heard of no issues of peripheral card compatibility from replica builders over the years. You are more likely to have peripheral card problems because of the other changes that were introduced to the bus than with USER1 being connected to the enable of the decoder at H12.

    There is a very minute possibility that you may have an issue with an unusual peripheral card that uses USER1 in an unexpected fashion. In this case, you can disconnect USER1 by carefully cutting the trace on the back of the PCB that leads from pin 39 (USER1) of the peripheral bus to the via that takes to the trace to the front of the board. Instead you could try cutting the trace where it connects to the via near the edge of the slot 7 connector. This will be more difficult because the ear of the connector partly obscures the via.

  • Stanford University’s “Apple 1”

    Wednesday, June 2nd, 2010

    Turns out that the Stanford “Apple 1” is an unpopulated Apple II, rev 0 PCB. The only other unpopulated A2 rev 0 I know of, is the one that the Hudson Brothers just sold. As rare as this is, it would have been nice to find a bare board Apple 1. By the way, during this investigation, an archivist at Stanford Library sent me the best image I’ve ever seen of the front of a bare original Apple II rev 0 PCB. More on that in the next post.