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> At 08:45 PM 2/10/02 +0000, Stuart Meier wrote:
> >After a spell on other things, I am back to a PIC project, and
> need to generate a 'Dong' sound (as in "ding-dong", without
> the ding..)

OK, this is a complete cheat, but a useful one, particularly
when you can't spare PIC time to synthesise sounds and a
beeper or piezo is just too noisy or coarse or inappropriate

The circuit attached can be tuned to many different sounds
from a click to wooden block to bass drum. It needs only a
trigger pulse. It's basically a decaying oscillator with a filter in
the feedback path. The components from the o/p of the gate
are optional but the sound will be grittier

The filter in this example is made of the two 68k and nearby
capacitors, with the decay time set by the 1M pot. The two
150k and the 2n2 also have an effect on the tone

I use it in applications like keypads (for audio feedback) and
simulating clock sounds in digital timers. Did plan to make
a rhythm generator once, but, nah, why bother. You can use
a basic 1-transistor amplifier with a small speaker or an audio
amp (TBA820, LM380 etc) for better quality. If, by "dong", you
mean a bell sound, that's more complicated. To do a bell
properly you need to modulate two sine (or at least not square)
waves together. It is possible to simultaneously trigger two of
these decaying oscillators and mix the outputs via a voltage
controlled amplifier to get pretty close to a bell sound


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