help with siren circuit and CD4017

[mohsen 2012]

Hello , this is a siren alarm circuit :


the sound of siren will change by changing the value of Rs , so i want to add a circuit maybe with cd4017 for automatic changing the sound , i want a 5 sound.
and i want to know how can i change the speed of the 4017
thanks

 

[Audioguru]

Rs changes only the loudness of the sound. A CD4017 is a digital sequencer with 10 outputs. Its outputs are not a tone and cannot feed the speaker.
What do you want the 5 sounds to do?

 

[mohsen 2012]

i want to make a car multi-siren ,yes the sound do not change much, but the tone changed .
and i want to learn the 4017 ic

 

[Audioguru]

When a digital oscillator feeds the Clock input of a CD4017 then it causes its outputs to sequence one-at-a-time and it goes high. It has 10 outputs but if one is connected to its reset input then that output resets the count to that number of outputs. A CD4017 can be used to make an LED Chaser but it cannot change the Rs in the siren circuit.

 

[mohsen 2012]

Is there another solution ??

 

[Audioguru]

The circuit is too simple to be able to change its sound by changing a resistor value in series with the speaker.

 

[c_mitra]

You need to follow steps systematically.

What is a siren (I am talking about sound: not the other kind)? One high frequency sound being modulated with a low frequency sound.

You must follow simple steps:

Design a circuit that can produce a high pitch sound.

Design another one that can produce a low frequency (may be inaudible) sound.

Design a mixer that can modulate the high frequency sound with the low frequency one.

Amplify the resulting sound and feed to the speaker.

Do all the things separately first and finally integrate them together. It is not at all difficult.

I do not understand how your circuit works; but I also think you too do not understand the circuit. Rs can change the volume of the sound but changing the volume this way is a lousy way to control the volume. It does nothing to change the frequency. If I can understand this, then anybody can.

 

[Audioguru]

What is a siren (I am talking about sound: not the other kind)? One high frequency sound being modulated with a low frequency sound.

Where on Earth does a siren sound like that? Do you mean Amplitude Modulated?
In North America a siren frequency ramps up then ramps down over and over. That is FM.
In Europe it goes high frequency, lower frequency over and over. That is also FM with a square wave for the modulation.
I think this circuit is a single frequency buzzer.

Mohsen, please explain which of the above this circuit sounds like.

 

[mohsen 2012]

 

[Audioguru]

It sounds like a squeaky car alarm, not like a siren. Car alarms usually make that noise when the wind rocks the car a little.
The frequency ramps up then suddenly goes down then ramps up again, over and over.
Changing the value of Rs causes transistors Q4 and Q5 to be overloaded which affects the oscillation.

I re-drew the schematic to show the SCR and oscillator better:

 

[c_mitra]

In North America a siren frequency ramps up then ramps down over and over. That is FM.
In Europe it goes high frequency, lower frequency over and over. That is also FM with a square wave for the modulation.

Do you know the lower and upper frequencies? We also need to know the frequency of the triangular ramp or the square wave. That will make it a tritone (one inaudible) device. To be effective it must cover more than one octave.

I always thought the sound is being amplitude modulated.

 

[Audioguru]

I used the video, my hearing and the program called Audacity to make the squeaks from the car alarm. The starting lower frequency is about 1500Hz and it ramps up to 2400Hz. It repeats at about 2Hz.

 

[c_mitra]

I too used the same tools but found a number of different tones and combinations: https://obrazki.elektroda.pl/3203958800_1455385711.png

 

[chuckey]

In the UK most emergency services use a two tone system, a high tone (1KHZ?) and a low tone (400 HZ?) and switch between them at a rate of 2 HZ or so.
Despite AudioGuru's attempt to redraw the car alarm circuit, it is still rubbish for this application. Rearrange it into a normal astable, with the bits left over you will be able to convert it into a two tone alarm.
Remove Q1, Q2, R1,R2,R4,C4. Short out position of R4. Now powering the circuit it should squeak all the time, you have built an astable! Now reducing the voltage at point B on Audioguru's circuit should increase the frequency of the squeak. C2 and C3 may need increasing if the sound is too high in pitch.
Build another astable with a time period of 2Hz and feed one collector into point B via a suitable resistor and it should two tone.
Frank

 

[Audioguru]

My neighbourhood has a dog that howls like a ramp-frequency-up then ramp it down siren when it hears a siren. There is a big hospital near my home and plenty of ambulances go there.
The dog has very sensitive hearting and begins howling long before we can hear the siren.