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I am new to electronics, and would like to make a low frequency buzzer.
is it possible to wire a capacitor in series with a resister to produce a pulse that would drive a minature speaker
would this work? if its feasible, any advice about values would be much appreciated,
With an AC source, yes (I mean an AC output adapter, not straight from the wall!). If you want to use a DC source you will need an active component, such as a 555 timer. It can be done with a single transistor and some passives. In general, if I'm not mistaken, passive components alone (resistors, inductors, and capacitors) cannot introduce new frequencies. They can only attenuate or shift them.
Mmmmm not as easy as I was hoping, but not insurmountable, it's for a portable project so would be need battery driven, don't really care
what frequency it is just can't use a high pitched scream,
Simplest is a tiny SPDT relay in series with coil in series with tiny speaker, and in series with NC contacts from 3V CR123 battery on a 5 V relay or 9V battery on a 12V relay. Just enough to make it buzzzzzzz... Speaker is optional as it makes a buzz on its own.
Thanks so much, I think you have found the answer, all I really needed was a noise,
I happen to have a suitable relay rated at 3v and a selection of batteries, as you suggested don't need speaker,
would the coil have to be of a particular value, can you suggest ?
I was suggesting a 5V coil on 3V because the relay wont last very long due to arcing, perhaps a small RF cap may reduce or the arc or make it worse. Depending on relay quality and switch off current the life can be 50k or 50m cycles. so at 300 Hz, use the time wisely. Also a reverse diode across the coil may help.
You said you do not want a high pitched scream (from a piezo beeper). Then do you want the irritating buzz from a 555 IC or relay or do you want the peaceful hum from an electronic sinewave oscillator and power amplifier driving a speaker?
Thank you all for your suggestions.
As one of my first projects (I guess I just wanted to make something useful,) so I thought I could put together an audible alarm for a friend whose ears are better than his eyes.
True I don't want it to be irritating to him, but it will only be on for a few seconds, and did want something simple.
I have a few components, but am lacking in knowledge.
Thanks Tony,
found the article on haptic feedback very interesting, even more ideas to follow, I guess the sound could be adjustable to a certain extent by inserting a pot ?
Thank you all for your suggestions.
As one of my first projects (I guess I just wanted to make something useful,) so I thought I could put together an audible alarm for a friend whose ears are better than his eyes.
True I don't want it to be irritating to him, but it will only be on for a few seconds, and did want something simple.
I have a few components, but am lacking in knowledge.
Thanks Tony,
found the article on haptic feedback very interesting, even more ideas to follow, I guess the sound could be adjustable to a certain extent by inserting a pot ?
Assuming the coil is very low resistance at 3V like less than 50 Ohms, the pot would have to be wire wound and equally small in same value to run at half the current being around the point it might stop oscillating.
The mechanical delay from open to close cycle determines the buzz rate and the more current means the more force to accelerate this rate.
The gap on the relay contacts also affects the travel and thus the rate and amplitude of oscillation, so that smaller strokes would sound more like a mosquito.
If the wire wound contact is not robust or of sufficient current rating 50mA?, it too will wear out quickly.
Also if no diode is across the coil in reverse the polarity, the spike voltages across the contacts would be like that of the old gaff handshake toy of the 50's? and 60's and early 70's... hello ...bzzzzzzzzz ouch... haha
from V=L dI/dt
Before Radio Shack left Canada all their stores had their "ding-dong" motion detector at the door and it sounded AWFUL because it produced an irritating squarewave buzz instead of a smooth mellow sinewave tone.
At work we needed one at the rear door so I bought the Radio Shack one and added a filter to smooth the squarewave into a sinewave then it sounded very good.
A mechanical buzzer or relay and a 555 IC produce irritating squarewaves.
A dog with two tails and a mile of lamp posts comes to mind,
Spent all day "playing" (Mrs out)
Thought about all your suggestions, which at times sent my mind reeling, but put them all together and come up with a prototype,
it consists of a motor with an out of balance flywheel and a battery, (thanks to Tony and his short cut to accentric motors)I found that the volume can be altered by attaching to plastic sheet or rubber mounting, (always have been better at engineering than electronics,)
also found frequency can be adjusted with a pot' in circuit,
Took ideas from you all, comments from, irritating "buzz" to "hum" of a mobile phone etc,
It may not be an ideal answer and its far away from my original thread, but it's just what I wanted, (plus, it cost nothing as I had The Parts)
thank you all again for your time, knowledge and patience,
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