[TUHS] Monitoring by loudspeaker (was: BTL pranks)

[Dan Cross]

On Sun, Jul 12, 2020 at 7:59 AM Michael Kjörling <michael at kjorling.se>
wrote:

> (This should probably be on COFF because I don't think this has much
> to do with UNIX.)
>
>
> On 11 Jul 2020 22:22 -0400, from doug at cs.dartmouth.edu (Doug McIlroy):
> > a loudspeaker hooked to the low-order bit of the accumulator played
> > gentle white noise in the background. The noise would turn into a
> > shriek when the computer got into a tight loop,
>
> How did that work? I can see how tying the low-order bit of the
> accumulator to a loudspeaker would generate white noise as the
> computer is doing work; but I fail to see how doing so would even
> somewhat reliably generate a shrieking sound when the computer is in a
> tight loop. Please, enlighten me. :-)
>

I would imagine a cap as a low-pass filter and a transistor as a poor-man's
analog comparator triggering a tape player on loop.

        - Dan C.
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