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Thread: Arduino-based front panel for QBUS backplanes

  1. #1

    Default Arduino-based front panel for QBUS backplanes

    Just thought I'd post a link here to a new Arduino-based project.

    The Arduino monitors some front panel switches (Power On/Off, Run/Halt, LTC On/Off, Restart) and provides the necessary output signals for the 10-pin connector on the rear of a QBUS backplane (BDCOK H, BPOK H, BEVNT L, BHALT L).

    As part of the power-up/power-down sequence for the PDP-11, it also turns an ATX power supply on and off, to power the backplane.

    The LTC output defaults to 60Hz, but can also be configured for 50 Hz by adding a jumper.

    The hardware is very simple: just an Arduino UNO. No Arduino "shield" or I/O electronics are required. You will of course need to wire up the front panel controls (4 switches and 2 LEDs) and fabricate the cabling to the ATX power supply and to the QBUS backplane.

    Here's the link ->

    Feedback and bug reports are most welcome.


    20170714_084652 (Medium).jpg 20170714_101334 (Medium).jpg

  2. #2
    Join Date
    Sep 2006
    Silicon Valley

  3. #3


    Thanks Al - I've added a link to your project on my project page.

  4. #4
    Join Date
    Jan 2010
    Central VA


    Do note that cooling is not *optional* for QBus backplanes -- you can and most likely will cook your CPU board without a fan! A desk fan aimed at the side of the card cage, allowing air to pass over and under all of the inserted cards, would be sufficient.

    Quote Originally Posted by Al Kossow View Post
    Ouch! $30 USD for something John Wilson whipped up to start with!

  5. #5
    Join Date
    Aug 2009
    Oslo, Norway
    Blog Entries


    Nice project, nicely documented, well done!

  6. #6
    Join Date
    Mar 2004
    Wilmette, IL (north of Chicago)
    Blog Entries


    @glitch - The main cost of Brad's setup seems to be the raw board priced at $20 - something like this is probably a $5 item from OSHPark. The rest of his BOM is only $7 and he's offered up the source and schematic, so not really a bad deal.


  7. #7


    I thought I'd resurrect this thread to show off my own interpretation of Malcom's excellent Arduino-based QBUS front panel. Mine is based on a knock-off Arduino Nano that cost around $4, plus a smattering of other parts. It's minimal, but quite functional for my purposes.

    Note that the switch labels have yet to be added in these photos. The switches are (L to R): Power, Run/Halt, LTC Enable/Disable and Restart.

    Mine runs a slightly modified version of Malcom's software that adapts it to the Nano. I've contributed this code back to him for future inclusion on his project page.

    A big thank you to Malcom for developing this and making it available to the community. Anyone looking to build a skeletal QBUS system should definitely consider throwing one of these together.


  8. #8
    Join Date
    Jun 2014
    Salt Lake City, Utah



    Nice job on the write up.

    Last year I did one using ttl and discreet components on a bread board, lol... It's still on a bread board.


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