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2N3055 heat sink

audioguru

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Here is a much more simple version of a European siren using 555's. Both 555's use the symmetrical astable circuit from the LMC555 datasheet.
Your circuit Will Not Work because the LMC555 has a low output high current of not much more than only 10mA. The 39 ohms resistor in series with the base-emitter of the transistor is a short circuit to 10mA. The 555 switches when its pin 6 voltage reaches 2/3rds the 13.2V supply which is 8.8V. But then the output current from the 555 must be at least (8.8V - 1V)/39 ohms= 200mA. An LMC555 cannot do it and an ordinary LM555 or NE555 can barely produce the required 200mA.

Gary, the TDA7241 is not available anymore. Use a similar but more modern TDA7396 car mono amplifier instead.
 

AnalogKid

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I whipped out the schematic from memory of something in the past. For totally unknown reasons, I had it in my head that the CMOS 555 output could do +/-200 mA. Wrong. I'll edit the posting.

ak
 

gary350

Well-Known Member
Your circuit Will Not Work because the LMC555 has a low output high current of not much more than only 10mA. The 39 ohms resistor in series with the base-emitter of the transistor is a short circuit to 10mA. The 555 switches when its pin 6 voltage reaches 2/3rds the 13.2V supply which is 8.8V. But then the output current from the 555 must be at least (8.8V - 1V)/39 ohms= 200mA. An LMC555 cannot do it and an ordinary LM555 or NE555 can barely produce the required 200mA.

Gary, the TDA7241 is not available anymore. Use a similar but more modern TDA7396 car mono amplifier instead.
Maybe that is why TDA7241B is selling for $30 each on ebay.

I bought a TDA7291 duel output 15w per channel audio amp operates on 12vdc, on a PC board already built for $2.95 free shipping from China, all I have to do is put my 555 output into the 15w amp input, connect my 2 speakers, connect 13.2v car battery. I can't build my own this cheap. I can found out if it works. This might be someones Christmas gift in about 6 more months. Or it could be something else. Once I connected a mercury switch to my cousins vehicle horn every time he put on the brake to slow down at a traffic red light mercury went forward and his horn blasted the person he was stopping behind. LOL. I had it connected with alligator clips he pulled over did a search and unhooked it. LOL Next day we both had a good laugh about it. :)

119036
 
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AnalogKid

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With an external audio amplifier, the circuit in post #111 will work as shown. Delete R3 and Q2, and take the audio output directly from U2 pin 3.

ak
 

AnalogKid

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Just for grins, here is another circuit for a European-style siren. One CMOS hex inverter handles both oscillators plus output transistor drive.

U1A and B are the same functions as the two 555's in previous circuits, with a switched timing capacitor as in post #111. The exact frequency is a bit harder to predict because the two Schmitt trigger transition levels are not as tightly specified and controlled as in a 555; the equation is approximate.

U1C and E drive short, asymmetrical delay networks to prevent cross-conduction (shoot-through) currents in the output transistors. U1D and F square up the resulting delayed edges for fast turn-on and turn-off of the output transistors.

I went with power MOSFETs. but bipolar darlington transistors can be substituted with appropriate base resistors. The output transistors are acting as saturated switches for the greatest possible output volume. The schematic shows part numbers in my design library, but any appropriately-rated transistors (30 V, 5 A min.) will work.

ak
Euro-Siren-2-c.gif
 
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audioguru

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With a 13.2V supply, the Euro-Siren circuit will produce 5.5W into 8 ohms, 11W into 4 ohms or 21W into 2 ohms of buzzing. The fundamental 1kHz and 1.5kHz will be at half those powers. The Mosfets will not need heatsinks.
 

audioguru

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Gary talked about 1kHz and 1.5kHz. Since he probably wants to use a fairly small folded horn speaker then he selected those frequencies it can play. It sounds tinny with no bass. It would have difficulty producing the fairly low frequency of 486 Hz.

When stupid people are driving and they hear a siren nearby then they stop and block the path of a fire truck behind them. So the fire trucks have an additional very loud low frequency roaring sound device to scare them away.
 

AnalogKid

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For those frequencies:

Change C2 to 0.047 uF (47 nF) > 1519 Hz
Change C3 to 0.022 uF (22 nF) > 1035 Hz

ak
 

audioguru

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AnalogKid, I played with your circuit to get gobs more power: 20W into 8 ohms or 38W into 4 ohms. 72W into 2 ohms?
 

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gary350

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When stupid people are driving and they hear a siren nearby then they stop and block the path of a fire truck behind them. So the fire trucks have an additional very loud low frequency roaring sound device to scare them away.
LOL you got that right. LOL :D:D:D

TN has a pull over law, when people hear a siren they should pull over and get out of the way. That is not what really happens, when people hear a siren they slam on the brakes are park blocking traffic. Stupid people what part of pull over do you not understand?????

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shortbus=

Well-Known Member
Since he probably wants to use a fairly small folded horn speaker then he selected those frequencies it can play.
I don't think he knows to use that type speaker. He shows in post #7 and #60, a standard cone type speaker. He won't spend a little money on the correct transistors, do you think he'll buy a horn type speaker?
 

gary350

Well-Known Member
I don't think he knows to use that type speaker. He shows in post #7 and #60, a standard cone type speaker. He won't spend a little money on the correct transistors, do you think he'll buy a horn type speaker?
I am not using this siren on my vehicle. Horn will work great but I don't need a horn for this siren.
 
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