Repro Cromemco joysticks...

[Gordon JC Pearce]

On Tue, 2007-09-18 at 22:33 -0400, Bill Sudbrink wrote:
> woodelf wrote:
> >
> > Bill Sudbrink wrote:
> >
> > > 1) The manual calls for a 45 Ohm QUAM speaker.  All I have
> > >    are plain old run-of-the-mill 8 Ohm internal PC speakers.
> > >    My ignorance of basic electronics shines through...
> > >    30 minutes of googling and I'm not sure what QUAM means.
> > >    Anyway, can I substitute the speaker?  With some modification
> > >    to the schematic?
> >
> > I think B.G. micro has 45 ish ohm speakers.
> > They tend to be used in intercoms often I think as the microphone
> > or speaker.
> 
> OK, I see 32 Ohm (what's 13 Ohms between friends?)...
> the price is right.  Are they QUAM?

32 should be fine.  You could also stick a load resistor of about 47
ohms in place, and feed the output to an external amplifier.

The main reason for 45 ohms is probably because the speaker driver is
just a simple transistor driven by an IO pin somewhere.  If you used and
8 ohm speaker it would draw too much current and fry the tranny (and
possibly pull the 5v rail down as well).

Gordon