Adding EPROM messages to the Accu-Keyer Extended project

Discussion in 'Homebrew and Kit Projects' started by W0RIO, Apr 1, 2021.

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  1. K9LY

    K9LY Ham Member QRZ Page

    Nice work, W0RIO. My local ham club built the Accu-Keyer as a club project in the 70s. It was fun to gather at a member's home to stuff and solder the boards. I used mine for many years. Even added the Accu-Memory board (using 2102 memory chips) a few years later, re-packaging it with a regulated power supply into a wood-grained TenTec enclosure (one of many home projects for this budding engineering student). Eventually it was replaced by a MFJ keyer with non-volatile memory, but I still have that Accu-Keyer tucked away.
  2. W0RIO

    W0RIO Ham Member QRZ Page

    I built my original accu-keyer in the late 70s then I built the accu-memory board with the outboard LED display. I managed to squeeze
    it all into a 6x6x4 aluminum box that I built in Jr. High school metal shop. At some point, I managed to short the input and
    output pins of the LM309K 5V regulator and fried many of the soldered-in ICs on both boards. Oops ;-) talk about a free education

    I loved the keyer so much that I removed all of the chips from the accu-keyer board and installed those horrible "molex pin"
    sockets, and got just the keyer part functioning again. I never fixed the accu-memory board.

    Many years later, I removed the molex pins and replaced them with good sockets.
    The board had non-plated holes so it required a lot of repair work to fix the numerous lifted traces.
    I swapped in LS TTL chips and used the accu-keyer for many years.

    Just for fun, I recently re-built the LED display board from the accu-memory and stuck some 74LS247 chips in place of the
    burned out 7447 display drivers, then I re-wired the board to have leading zero blanking. The LS247 chips add the top segment to
    the '6' and the bottom segment to the '9' for better looking digits. The 7 segment displays also had to
    be replaced since they were fried in the earlier power supply apocalypse. I now have a handy 3 digit TTL counter.

    For fun, I connected the counter's clock input to the output of my new accu-keyer extended project and noticed that it sensed
    an extra pulse when the keyer was sending dashes. That was cured by adding yet another R-C delay to the keyer output signal.
    The original accu-keyer actually has quite a few little glitches that need extra R-C delays to fix. It *was* designed in
    the early days of TTL, so that's not too surprising.

    This is a homebrew project that I've been working on for nearly 45 years, it was overdue for a complete new build,
    hence the accu-keyer extended project. Did I mention that I LIKE playing with TTL chips?

    In around 1990, I used a Motorola 68HC11 EVB (evaluation board) to make an interrupt-driven iambic keyer using 6811 assembly
    language. That project worked quite well, but the board was re-purposed for another project. I may try to revive that project.
    K9LY likes this.

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