Beeper Circuit With Variable Interval and Audio Frequency

Thread Starter

PADRC46

Joined Oct 15, 2019
5
Hi. This is my first visit to the site (I'm impressed), first post on the forums and I hope someone might be able to offer some guidance. Let me make it clear that I am very new to electronics, working on the basis of a specific need, and struggling to find a solution.

I'm sure that this is all pretty basic stuff, but a couple of days ago I didn't even know about RC networks, so please be patient!

I want to build a beeper circuit with variable interval and audio frequency output.

I found what seemed a likely looking basis, using a 556 timer:



And have built this on a breadboard

Powering the circuit up, I am getting no audible tone and the 100K variable resistor does nothing to change that. But I can hear a regular 'click', the interval of which is variable via the 500K variable resistor.

And I'm a bit stumped.

If my understanding is correct, on the pins 1-7 side, a capacitor of 2uF, R1 of 1K and R2 of 360K (notional values) would give me a 1 second on/one second off interval(?). On the 8-14 side 0.01uF/22K/100K should give a tone with a frequency of about 650Hz(?).

Does this seem reasonable?

Ultimately, I want the audio output to be line level via 3.5mm jack, but first things first...

Am I close? Or way wide of the mark in some way(s)?

Any advice would be hugely appreciated.

Thank you.
 

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Thread Starter

PADRC46

Joined Oct 15, 2019
5
I should add that all component values are currently as per the schematic, so both interval and frequency won't be as required as it stands, but should be giving me a regular beep of (I think) about half the audio frequency I want, though I#m not quite sure the interval times - according to an online calculator, it seems like T1 should be about 415 milliseconds, T2 about 346 milliseconds.
 

AlbertHall

Joined Jun 4, 2014
8,320
There are two different things called 'buzzers'.
One type makes a buzzing noise when a DC voltage is connected to it.
The other type works more like a loudspeaker. If you want a 3kHz note you must feed it with a 3kHz AC voltage.

The regular clicks leads me to think that you have the first type but the circuit requires the second type.
 

Thread Starter

PADRC46

Joined Oct 15, 2019
5
Thanks for your quick response. I interpreted the speaker symbol as indicating a good old fashioned magnetic speaker and that’s what is hooked up to the circuit. And I have since read that a Piezo unit wouldn’t need a capacitor in series? I had a suspicion that there might potentially be a problem here and have ordered a couple of options earlier today.
 

Audioguru

Joined Dec 20, 2007
11,251
Pin 8 should not connect to pin 5 but it is correctly connected to pin 12, the 100k tone pitch control and the 18nF capacitor.
Instead pin 5 output should connect to pin 10 reset.
 

Thread Starter

PADRC46

Joined Oct 15, 2019
5
Thank you Audioguru. I’ll try that - presumably, the connection from pin 10 to +V should be removed?
 

Thread Starter

PADRC46

Joined Oct 15, 2019
5
Bullet bitten, yes! Thank you very much. That works very nicely - just a little modification to get the pulse rate and audio frequency lower and I’m there with the circuit.

It remains to make the output suitable for line out (to suit earphones and a Bluetooth transmitter). I’ve looked at a couple of possibilities, but would like to keep it minimal and compact. Audio quality is not, in this instance, important. I briefly hooked the circuit up to some earphones with a volume control - too loud even at minimum, so it does suggest stepping down is necessary?
 
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