Jerry Stuckle writes:
> I'm not aware of a module - but there are a lot I don't know about,
> anyway.
> Just one note - it's the transducer which actually generates the sound;
> it's being fed with a DC voltage. Connecting headphones to this will only
> give you a click in the headphones (and probably blow the board due to the
> low impedance of the headphones).
There are piezo buzzer that actually work that way such
as the Sonalert modules found in smoke alarms and zillions of
other electronic devices that need to beep but the PC speaker
gets it's signal from the output of a thing called a
timer-counter chip whose part number escapes me at the moment.
The chip was used in the original IBM PC's and consisted of a
pair of timer-counters. One was set to divide the system clock
speed down to 18.2 Hertz for the real-time clock and the other
half could be programmed by the user to set various devisor
values for the counter which then produced a square wave
output that drove a speaker or piezo transducer. The old PC's
also had a transistor between the timer-counter output and the
speaker because CMOS chips don't have the wattage to directly
drive even a small speaker to any reasonable level.
I used to do a lot of 8086 assembler programming and
played a lot with that speaker driver. You could actually turn
the output of the transistor on without starting the timer and
hear a single click or turn it on with a count stuffed in to the
counter and it would generate a tone depending on what frequency
you set in the counter.
> IOW, don't even THINK of doing it :)
I probably won't go that route but one can do things
like that if one is careful and makes sure not to load the
output more than it was meant to be loaded or you certainly will
trash the board or cause other unintended consequences such as
sporadic glitches in it's operation.
Again, thanks.
Martin McCormick
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