Turning An Analog Scope Into A Logic Analyzer

scope

When [Marco] was planning on a storage oscilloscope build, he realized having a small device to display eight digital signals on an analog scope would be extremely useful. This just happens to be the exact description of a simple logic analyzer and managed to turn his idea into a neat little project (German, Google translation).

The theory of operation for this surprisingly simple, and something that could be completed in a few hours with a reasonably well stocked hackerspace or parts drawer in a few hours. A clock generator and binary counter are fed into the lower three bits of a simple R2R DAC, while the 8 inputs are fed into an 8-input multiplexer and sent to the last bit of the DAC. With nothing connected to the logic analyzer inputs, the output to the scope would just be an 8-step ramp that would appear as eight horizontal lines on the screen. With something connected to the logic analyzer input, an extremely primitive but still very useful logic analyzer appears on the screen.

While it’s not the greatest analyzer, it is something that can be cobbled together in an hour or two, and the capabilities are more than sufficient to debug a few simple circuits or figure out some timings in a project.

Comments

  1. Brane212 says:

    I did this long time ago on my Hameg HM412 ( 2 x 20MHz, 1980-ish production )

    But my version was integral – built into the scope. I had 8 channels for digital input.

    IIRC, they werent truely digital, just convenient for digital signals.

  2. thegraynomad says:

    I did that about 30 years ago, plus I used the Z axis to have a bright cursor.

  3. Json says:
  4. John says:

    Nice title but hardly correct. If I plug a DVD player into an old CRT television can I have an article on “turning an old TV into a DVD player”?

  5. Ted says:

    Found the Schematic, but what are the values for the components?

  6. Marco Seiller says:

    IC4 AD8055
    C1 & R10 for ca. 10kHz
    C2 & C3 47uF, Diodes: Schottky
    R2R-DAC: 1kR, 5kR Potis
    100k Pulldown at D0..7
    R11, C4-6 for ca. 100Hz, 3kHz, 50kHz

    The actual values of the frequency determining resistors are uncritical ;)

    Regards
    [Marco]

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