Piezo buzzers
Dear Tim,
First principles:
- a Piezo Buzzer works by passing a voltage accross a tiny sliver of Piezo crystal,
which vibrates when volts is applied. (IE the buzzer "generates it's own audible frequency")
NB that this is different to a Piezo Speaker or Tweeter, which requires an input "audio frequency" signal,
and cannot "generate an audible buzz" in-and-of-itself.
- Buzzers are commonly used as warning indicators in simple circuits,
because they do not need an amplifier,
and can be fed a straight DC voltage to "simply make a noise".
(simple, cheap, easy to integrate).
- Increasing the voltage (within sane limits) will increase the Volume of a Piezo Buzzer.
- Feeding a PWM square-wave into a Piezo Buzzer allows some degree of control over the audible frequency generated (limited by the natural resonant frequency of the specific sliver or Piezo crystal mounted in the Buzzer-in-question).
SOOOO, how dooes this help with your scenario?
1 - We are assuming these "Buzzers" are actually active Buzzers,
which generate their own audible frequency in respnse to a straight DC voltage input
(not "speakers" or "tweeters")
2 - we are assuming the PSX is dumb simple-enough that it's simply feeding the Piezo Buzzer with a straoght DC voltage, not something more complex like a tuned PWM signal.
3 - Therefore, to change the audible frequency, we need to change the behaviour of the sliver of Piezo Crystal inside the buzzer (possibly change to a different Piezo Buzzer unit altogether?),
OR
change the voltage/signal the PSX feeds the Piezo (IE change from straight DC to some form of PWM),
in hopes that we can inject some degree of "tune-able" audio frequency into the situation.
https://learn.adafruit.com/using-piezo-buzzers-with-circuitpython-arduino?view=all
Of the two options, the first is arguably more-do-able. Indeed, a quick google shows:
https://tonystrains.com/product/dcc-specialties-sonalert-for-psx-circuit-breakers
https://www.dccsupplies.com/item-p-101543/piezo-sounder-3-20vdc-suits-psx-units
...and a spin thru websites like DigiKey, Farnell/Element14, Mouser, etc
will likely provide various Piezo Buzzer options which come "tuned" to given frequencies...
It is also possible, although ugly, to artificially change a Piezo Buzzer frequency by applying "calibrated pressure" to the unit,
but this is an ultra fine-line bodge, which also affects the volume (dB-SPL),
and places extra stress on the unit., potentially causiing premature failure...
If you were _really_ creative, you coould replace the "stock Piezo Buzzer" with a SOIC microprocessor,
(think "really really tiny Arduino"),
which took the "as delivered PSX 'Piezo buzzer voltage' ",
used it as the SOIC Microprocessor's "DC supply voltage"
(thus "turning the SOIC unit ON"),
and using the SOIC's code-controlled Output to deliver a PWM signal (of appropriate frequency and voltage),
to a Piezo?
(OK, we're getting a bit Rube Goldberg here, but it's maybe the cheapest and fastest way to "convert" a straight DC voltage to a PWM signal, without kitbashing the PSX circuitry itself?)
I hope this helps...
Happy Modelling,
Aim to Improve,
Prof Klyzlr
