Gaps in the collection (was Re: rarest computers. )

[Tony Duell]

> 
> On 4 Aug 2004 at 5:18, Tony Duell wrote:
> 
> > Anyway, there's a little extra circuitry (transistor, a few passives)
> > to provided a simple amplitude envelope. Not just a sudden start/stop
> > beep, but one that tails away. 
> > 
> > No real benefit from having this, but that _was_ HP for you. 
> 
> Indeed, the same thing was done in the HP 64000 workstations.  They used a 
> 555 timer for the tone generator, a one-shot for the gate, but then added a 

Neat...

Talking of HP using 555 timers, they used one to drive the power-on light 
in the HP86 (and I assuem the HP97). The reset input goes to an output on 
the memory cotnroller chip (which is asserted if there's a self-test 
error), the LED (and series resistor of course) goes between the output 
of the 555 and the +6V rail. 

So the LED is dark if the machine is off, on steadily if the machine is 
on and no error (555 is held reset, so the output is low all the time), 
and blinks (controlled by the 555) if there's an error. 

IIRC the battery level circuitry in the 9114A and 9114B disk drives does 
something similar, with one of the LEDs driven by a 555. In this case the 
timing capacitor of the 555 is switched by the battery voltage detector 
so the LED either flashses too fast to see (and appears to be on all the 
time) or blinks visibly.

> transistor and an R-C circuit to provide a fast attack, slow decay 
> envelope, resulting in a characteristic "Bink!" sound.

That's what the 9830 circuit does too. I can't easily reproduce the 
schematic in ascii-art, and I don't have a scanner, but if anyone is 
seriously interested I will see what can be done.

-tony