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Anyone got Forrest Mim's Engineer's Notebook at hand?

Discussion in 'Electronic Basics' started by Al, Jul 7, 2004.

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  1. Al

    Al Guest

    Many, many years ago I built a little circuit from my much-loved copy of
    Forrest Mim's Engineer's notebook. It was based on 555/556 timers, and had
    a couple of pots on it which when twiddled caused the thing to generate some
    pretty spaced out sound effects. Recently, I remembered this great little
    device and decided to make one again. Can I find the book?! I turned my
    house and my parents house inside out, no luck :-(

    I thought I'd stumbled across the very circuit on the net:

    This looked like it was it! However, after building it I'm not so sure this
    was the circuit after all. This one just adjusts the frequency of the main
    oscillator with another oscillator, giving police siren or vibrato type
    noises. As you tweak one pot the main frequency varies, tweaking the other
    pot alters the modulating frequency.

    From memory (bearing in mind it was around 20 years ago) the project I built
    just emmitted a single continuous tone when the pots weren't touched. But
    while you were actually twiddling them it made all sorts of crazy whooping
    noises, which changed depending on direction and speed that you turned the
    pots. Fantastic!

    Here's where I start asking favours. If anyone's got a copy of the book to
    hand (in the UK it was an A4 sized yellow paper back, from Tandy
    (RadioShack)), would they mind just looking through it, and putting me out
    of my mysery - is there another sound-effects generator circuit, not the
    above one, that possible uses a couple of 556 dual timers?

    Just knowing whether or not my memory is playing tricks on me or not would
    encourage me to search harder for the book, but (and here's the really
    cheeky bit) if anyone out there is feeling really kind, perhaps they'd care
    to scan in the schematic and email it to me? :)

    That book was great by the way. What reminded me of the whole thing in the
    first place was finding the 10x10 LED array oscilloscope that I built from
    the book. Not the most useful bit of test gear in the world, but it really
    did work! I really want to find my copy again. I did look on Amazon but
    it's a bit expensive as it only seems to be available on import from US.

    Anyway, thanks for your time!


    To reply, just take the upper case
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  2. (blue in the USA)
    Could it have been a ckt using a 556 (dual 555)?

    P. 119 has a ckt called a "Sound Synthesizer", billed as
    an osc followed by a freq divider. "Adjust R1 and R4 for
    ususual sound effects", it says.
    Nah, copyright and all that. I can redraw it and post on
    the schematics binaries group (if you can get there) in a
    couple days.

    Mark L. Fergerson
  3. Emailed scan. This is the only one matching your description, and, as
    Mark said, it's on page 119.
  4. Zorknob

    Zorknob Guest

    $14.67 at That's dirt cheap. Just buy another copy.
  5. Al

    Al Guest

    Thanks everyone for your help. I've now built the circuit yet again, and
    it's exactly as I remembered - amazing the sounds you can get out of a £0.30
    chip, two caps, a resistor and a couple of pots!

    Great fun :)

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