1964 Antique MODEM Live Demo

[Gordon JC Pearce]

On Tue, 2009-06-02 at 18:54 +0100, Tony Duell wrote:
> > Okay, let's try again.  I have a circa-70s 300-baud modem, that will
> > generate incorrect tones when it's plugged into a USB-to-serial
> 
> Waht's the make and model of the modem?
> 
> > converter, but not when it's plugged into a real serial port.
> 
> Have you measured the voltage on the RS232 TxD pin in both cases?

Tony is closest ;-)

The USB serial adaptor only seems to put out a really tiny current.
More than a few microamps (!) into a load makes it put out a train of
spikes at about 20kHz more like a sawtooth wave, than nice neat pulses.

The VCO in the modem just spacks out totally when you feed it this.
Good for Aphex Twin-type noises, though.

Gordon