# Beeper Circuit With Variable Interval and Audio Frequency

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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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
9,647
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.

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
11,249
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.

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