Thursday, August 4, 2016

Replica completed, prepared to move to CHM tomorrow for VCF West


I tried to boot from the 1442 but the machine is acting cranky, giving read checks on the boot card. I might be able to loosen it up by doing this many many times if I have the patience tomorrow morning, otherwise I might not be able to use it during the exhibition.


I developed a couple of hand loop programs to use with the replica and the real 1130, to illustrate how the machine works. I also ran Mike Albaugh's art printing program which seemed to run fine - he may use my system and his program during the show this weekend.

This afternoon, I inventoried everything I will be bringing to VCF-W which I will turn into checklists for packing, setup, and removal time. I decided not to bring oscilloscopes, meters or other tools, because there will be surfeit of them at the show.


Once the electronics were ready to install, I had to mount the display pedestal on the base. This was a challenging task. I had to cut tails off the pedestal base in order to slide the pedestal into place. I also had to cut the wood stands inside the pedestal posts so exactly 1 5/8" stuck out beyond the metal post.

With the pedestal in place, I put a selectric mechanism on the base, laid the console entry switches in their place, and began to connect things up underneath. I had to suspect the fpga and its extension board on the back of the gray cover just below the pedestal base, then lay the keyboard assembly onto the frame.

Wires were routed and then I did the ticklish assembly of the gray metal cover over the keyboard, avoiding damaging or shorting my circuit boards hanging off the rear of the keyboard assembly.
Next was the placement of the power supplies, which need to be up high near the board or I would need to lengthen the wiring to the connectors to allow the power supplies to sit at the bottom of the frame.
Replica before power-on test
Finally, everything was in place and hooked up - time to do a power on test and validate the connections are all correct. Unfortunately, I had swapped the +12 and the +20 connectors to the keyboard aux board - the power supply couldn't come on at all because of a short circuit, but I think it damaged something before I realized what happened.

The processor works but I don't have any lights - pretty crucial to the replica exhibition. There are two cases here - 1) I blew something on the aux board or on the fpga itself, but the light display circuits in the pedestal are still okay. or 2) the pedestal circuits got fried. If the latter, it is game over, can't be fixed in time and the replica stays here.

I do have a second fpga board and can reroute the lights to avoid using the aux board at all. If we are dealing with case 1, then I will have lights and a replica at the show. Time to reroute the LED signals to one of the connectors on the fpga board itself. I moved them, generated a new bitstream, and loaded that in my backup Nexys2 board.

I carefully hooked the new board up to the console entry switches, pushbuttons, display pedestal and rotary mode switch, then fired up the system. I was ecstatic to discover that I have lights, buttons and a good replica.

We will need to be very careful in moving the replica to avoid damaging or undoing connections. Just as with the real 1130, kid gloves are needed.


I got the rotary switch working, but haven't got the display lights running yet. After they work, the remaining challenge is the input board and keyboard I2C link. If that all works, I can button up the unit into the frame and be ready to roll.

The display lights are now running nicely and I moved on to testing the console entry switches. Each test requires a run through the Xilinx ISE tool chain, which takes more than 30 minutes to complete. Cobwebs are growing on me as I wait around for each little test.

Good console entry switches, leaving only the testing of the input board. This will be a bit funky because the board I am using has only one of the two multiplexor chips installed, which might require me to change the logic in the fpga that cycles through the various chips.

I decided to extend the cabling from the keyboard aux board, for two reasons. First, the existing solid wires snap off the connectors too easily, but more importantly the length must be increased so that I can locate the FPGA back under the pedestal base. Quite a bit of cutting, soldering, connector preparation and insulating, but it was eventually done.

Now it is time to wire in the input board to the fpga extension card and to power. If I can get these to work right, I will have everything I need for the replica to work as it used to. I intend to wire up the power switch to the power supply, replacing the temporary switch I was using.

The first shot at running everything did not pick up the buttons - probably because my logic for reading the multiplexors was written for four chips - two on the original input board, one on the keyboard board, and one for the console entry switches. With two missing, my state machines are probably stalling because of the lack of response.

I hope that the board I used was wired for the chip address I expect - if so, then my modification to the logic to jump only between chips 1 and 3 should work. If the address is not what I expect, I may have to test the board to verify the actual address in use and modify the logic accordingly. Thirty minute wait until the test could be run.

I am still getting nothing on the link from the input board and keyboard aux board multiplexors. I could wire the six switches to open inputs on the fpga itself, bypassing the need to get the input board working. Since I don't have a debounce anyway, it made sense to just go with the direct wiring method for now.

Once this tested out good, my replica pedestal was ready to mount on the base and to put it all together. This is ready for transport to the festival.


  1. Excellent work and safe travels.

    What keycaps did you use for the keyboard and where did you obtain them?

  2. Wow! The replica looks absolutely stunning now! Looking forward to see you tomorrow.

  3. Hi Grant. I made a mold of keycaps from the keyboard which were going to be replaced, cast replacements, painted them the right color, made lettering transfers, then clear coated them with spray paint to protect the lettering.

  4. Hi Marc

    Rough around the edges when you get close - especially the covers and other parts I made in a rush this week to make it cosmetically more complete. The logical behavior was complete from years ago.