# Siren schematic: What controls the cycle speed?

• cf8
In summary, The conversation is about creating a siren sound using a schematic, specifically altering a component to change the cycle time. The suggested components to alter are R1, R2, or C1. Changing the capacitor to a smaller value will result in a quicker alarm rate. There are calculators available to help with this process, and LTSpice can be used to simulate the circuit. The conversation also mentions using an Arduino, but no information was found on how to do so.
cf8
I found http://www.uoguelph.ca/~antoon/circ/wailing.htm" schematic for creating a siren sound, but I can't figure out which component could be altered to change the cycle time of 6 seconds.

If I had to guess, I'd say either C1 or C4, but I'm really lost as to how this schematic works, so I don't know. Also, am I correct in thinking that the smaller the value of the key capacitor, the shorter the cycle time?

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You would change R1, R2 or C1. making any of them smaller makes the period shorter.
If you change the resistors, you should keep them in about the same ratio (about 1 to 10 ) if you want the same up to down ratio as it has now.

I would make the capacitor smaller if you want the alarm rate to be quicker. 6 seconds does sound a bit slow.
25 uF would give about 1 second up and 1 second down so 2 seconds total.

There are lots of calculators for doing this:
http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm
seems OK.
They use the formula
Frequency = 1.44 / ( (R1+R2+R2) * C) where resistor values are in OHMS and capacitor values are in FARADS. So, 25 uF is 25 E -6 FARADS on a calculator.

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Wow, that's lots of information; it should be just what I need. Thanks!

You could simulate the entire circuit in LTSpice; they have the NE555 timer under misc components.

Bob S said:
You could simulate the entire circuit in LTSpice; they have the NE555 timer under misc components.
Interesting. I might have to try this the next time I boot into Vista. (I primarily use Ubuntu.)
I was originally looking for some way of using an Arduino, but I couldn't find anything.

## 1. What is a siren schematic?

A siren schematic is a diagram or drawing that shows the electrical components and connections of a siren system. It is used as a guide for building or troubleshooting a siren.

## 2. How does a siren work?

A siren works by using an electrical circuit to power a motor or fan that rotates a rotor with holes or slots. This creates a pulsating air flow, which produces the distinct sound of a siren.

## 3. What controls the cycle speed of a siren?

The cycle speed of a siren is controlled by the frequency of the electrical signal that powers the motor or fan. A higher frequency will result in a faster cycle speed, while a lower frequency will result in a slower cycle speed.

## 4. Can the cycle speed of a siren be adjusted?

Yes, the cycle speed of a siren can be adjusted by changing the frequency of the electrical signal or by adjusting the mechanical components, such as the size or shape of the holes or slots in the rotor.

## 5. Why is the cycle speed of a siren important?

The cycle speed of a siren is important because it determines the rate at which the sound waves are emitted. This can affect the loudness and perceived urgency of the siren, making it an important factor in emergency situations where the siren is used to alert people.

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