Thursday, June 9, 2016

Back to work on the new GUI for the 1130


The lamps used for the 1130 system are glass incandescent bulbs with bare wire emerging from the glass envelope, but the wires have become brittle with age and easily snap off at the surface of the glass. To make this more complex, the bulbs are inserted in a socket which is inserted over pins on a control board, making contact by squeezing the bulb wire between the pin and its mating hole.

The boards have SCRs to modulate the 7.5V AC lighting power based on the logical state of the digital SLT signal line. A board is a narrow PCB, eight to sixteen lights wide and about 1/2" deep, with pins emerging from one edge to slide into the lamp sockets. Eight signal lines are connected to the eight SCRs, as well as the 7.5VAC and ground common lines.

The display pedestal has a plastic honeycomb with holes that the bulbs and their sockets should fit into. In theory, the sockets form a firm fit into the honeycomb holes with the control PCB hanging off the back of the lamps. The bundle of wires hooked to the PCB, however, pull back and down on the boards, tending to dislodge them.

Forcing the 16 independent sockets to fit into their honeycomb holes will often snap one or more of the brittle lamp wires, so that it appears to be intact but is electrically isolated and dark. The scheme is not well designed for replacement by the CE, requiring fiddling to insert or remove a row of lamps with their board.

It would have been ideal if all the boards were anchored to a common plate, spaced properly, with the lamp sockets aligned properly so that the plate is pulled back or pushed into the honeycomb as a single unit. Pulling the plate back would allow access to all the lamps but minimize the impact on every other lamp but the one being replaced.

I am looking at ways to clean this up, ranging from the common plate idea plus socket aligners, or other means. One possibility is to find reasonably compatible lamps which are modern, without brittle leads, and build new mounts to hold them in the honeycomb. I could then mount the control PCBs back a bit and connect these to the new sockets via wires.

Of course, if I could find modern incandescents that were compatible with the control board, that would not snap off at the merest movement, and that could be fit into the sockets used with the current bulbs, I could assemble the panel as it is currently designed.


Restructuring the GUI

The first problem I discovered in my recovered laptop environment was that I had installed the 64 bit version of wxPython but the base Python version was 32bit. Uninstalled the old one and downloaded the correct version, then moved ahead.

Next up was the usb module (and the problem I remember having to manually move DLL files to get the USB support working).  Installing pyUSB was easy, and yes the darned libusb-win32 was a obscure mess.

I didn't have the USB module configured yet when I tested, raising some exceptions that I coded around so that the application handles this condition gracefully. Next, I got the driver installed, allowing the application to come up and attempt communications.

My next issue is the same one I had with the old GUI when I tried it - the GUI times out trying to read a response from the fpga. I will have to put in some diagnostics to understand the state in the fpga when this happens.


  1. I've made some purchases from, take a look at this page:

    There also exist,, and, but their searches are not as convenient.

    Whatever, I would think the odds of finding any bulb rated for a 7.5v supply would be slim.

  2. Hi David

    The bulb used with the circuit is a 4.5V 140ma bulb. Since the power supply is 7.5VAC but an SCR is used to switch the lamp on or off, it is only conducting for half the sine wave and the average power delivered is equivalent to a steady 4+ V source.

    Easier to find a 4.5 or 5V bulb rather than 7.5, but I need to match a few characteristics, not just voltage and brightness, to fit properly in the space provided.

  3. I will look at those sites - thanks for the reminder and variety of suppliers.