Arbitrary waveforms from a scope

arbitary-waveform-250.jpgAn arbitrary waveform can be generated by cutting it out of cardboard and holding it against a scope display.

I wish I could credit this idea to the right person, but sadly I saw it in a magazine too long ago for me to remember the inventor’s name, or the magazine.

A photodiode pointed at the screen and connected to the Y deflection input with the correct polarity, combined with the right gain setting on the scope, makes the spot follow the edge of the cardboard.

The connection to the Y input is also the output of the generator, with amplitude set by the Y gain (assuming there is enough gain after the photodiode).

Repetition rate depends on the timebase setting.

When I tried it out of curiosity, also years ago, it worked well – even without making the room completely dark.

You do get an aberration during fly-back (or its digital equivalent).


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  1. 'Alice'
    January 04, 2013 09:52

    Nice to hear from you again Mr Kurt.
    It is such a clever and cunning idea, I wish I could credit the inventor.
    I was pondering reasons it would not work on a digital scope and could not think of any.
    I tried it on an analogue scope (we don’t have analog scopes on this side of the pond :-) That said, it was from Tek, so it probably was an analog one.

  2. Steve Kurt
    January 03, 2013 02:03

    I think this wins the award for the most non-intuitive method for generating a wave. Does it require an analog scope, or would a modern digital scope work too??

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