What is the best Power Transistor to use for a 555 Horn/Siren?

[gary350]

I need a horn/siren for my bicycle. I built the circuit in the TTL Cookbook. It works but it is not loud enough for a bicycle. What is the best power transistor to use for this circuit? I'm not sure how much power I need, maybe 10 watts. I have some tiny 10 watt speakers.

My plans is to use a Green button to turn on the 555 time on the right for Horn only. The Red button will turn on both 555 timers for a siren. I think a diode between the 2 timers will block voltage to the first timer when the green button is pushed. What is a good choice for the diode? I have a 100 pack of 1N4007 diodes.

A 12vdc rechargable battery pack will probably work good for this.

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[audioguru]

The squarewave "buzz" from a 555 can drive a transistor to turn on and off. Then a speaker receives DC pulses instead of the AC it was designed for. If you have an 8 ohm speaker that works with 12VDC pulses then its current when it has 12V is 12V/8 ohms= 1.5A. The speaker is powered only half the time by the squarewave so its power is (12V x 1.5A)/2= 9W. The speaker will probably work better if it is fed AC from an audio amplifier circuit.

A tiny speaker makes a high frequency "squeak" sound. You need a larger speaker to make the lower frequency buzz sound. A triangle waveform or a modified sinewave at even a lower frequency would sound more like a horn.

 

[Reloadron]

You may also want to think about a smoke detector piezo buzzer. Find an old smoke detector and hack the piezo buzzer out of it. Then build around that. My guess is you want high volume and getting there with a speaker can be difficult. Smoke detectors are designed to scream loudly using little power, typically a 9 volt small battery.

Ron

 

[gary350]

I experemented with a 2N3055 transistor only because I have one. I bet there is a better transistor than this. I also have 2 old DS-501 transistors. I dont have many power transistors laying around, I dont know which one to buy?

I have several small 2" speakers, 5w, 7w, 10w all 8 ohms all with a 1/2 lb magnet. These are good quality speakers maybe better quality than I need. All they need to do is make noice, it does not need to be high quality sound. A speech horn might work better.

If I had a junk smoke detector I would experement with it. Lowe's and Home Depot want $27 for a new smoke detector.

 

[Nigel Goodwin]

I experemented with a 2N3055 transistor only because I have one. I bet there is a better transistor than this.

I'd probably use a TIP41 (NPN) or TIP42 (PNP) - and the speaker needs to be in the collector - not in the emitter.

 

[gary350]

What do you think about this, I found this circuit online?

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[Nigel Goodwin]

That would be fine, and removes AG's 'DC problem'

Presumably you're wanting it LOUD?.

 

[Tony Stewart]

Buzzers with piezo are most efficient and can exceed 110 dB from 12Vdc usually in the 2~4 Kz range. Cheapest onces for $0.35 might do almost 80 dB.
Magnetic buzzers at low cost will do 95 dB from 400 to 4kHz fixed.
Both come in internal or you supply external drivers.

You can add a horn shape to boost in one direction.

Closer to 1kHz is better for ear response and pulsing at 1Hz rate will mimic a truck backing up.

You can pulse the DC for internal buzzers or sweep for different effects.

Personally, you might want an air horn for some drivers or just a jingle bell for others.

Steve Gibson started a Google group for Dog noise abatement with largish ultrasonic horns.

Pulsing is a good idea to get attention with variable rep rate for more effect.

Speakers might work if high efficiency midrange horns in low kHz range but not as loud as buzzers that resonate for higher Q.

https://www.digikey.com/product-sea...ee=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=25

 

[gary350]

That would be fine, and removes AG's 'DC problem'

Presumably you're wanting it LOUD?.

How many watts is that? This has to be battery powered.

 

[alec_t]

Isn't the diode in that circuit the wrong way round?

 

[audioguru]

The circuit with the TIP41 and TIP42 transistors does not need and does not want the 100 ohm resistor reducing the base current because the transistors are emitter-followers. Each transistor limits its own base current.
With the 12V supply, the output high voltage of the 555 with the load is about +10V and the base-emitter voltage drop of the TIP41 is about 1V so the emitter goes high to +9V.
The output low from the 555 is about +2V and the base-emitter drop of the TIP42 is about 1V so the emitter goes low to about +3V. Then the speaker gets a voltage swing of about 6V peak-to-peak.
The power in the speaker is (6V squared/8 ohms)/2= 2.25W.

A tiny speaker that is only two inches in diameter is a fragile tweeter that plays only momentary high frequencies. It is not strong enough to play a continuous tone. Its power rating is its momentary peak allowed power. A larger speaker can play a continuous tone and if its manufacturer tells the truth then it can play a continuous tone at its power rating.

 

[Nigel Goodwin]

How many watts is that? This has to be battery powered.

The most you can get off 12V is about 4W to a 4 ohm speaker, or 2W to an 8 ohm one - bit more in this case though, as it's not attempting to be linear.

 

[audioguru]

I think a 3" or 4" speaker should be used and the 0.1uF capacitor value should be increased to 0.33uF so that buzz tone is 303Hz. The speaker needs to be in a housing so that sound from its rear does not come around and cancel sound from its front. A computer speaker in its own housing will work.

 

[gary350]

I found this circuit.

 

[audioguru]

The circuit you found increases the 12VDC to 20VDC. It operates at a fairly high frequency allowing its output filter capacitor to be small. You need AC at a fairly low frequency.

 

[gary350]

How about this? I have a 15w and 75w speaker both are 6".

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[Tony Stewart]

The DC may push the coils outside their linear range. How about a stereo Amp chip with differential drive.

No DC and twice the voltage.


Errhm I think you meant NPN in #16

Push pull driver may be better than common emitter depending on resonant frequency.

This needs inverting and two complementary Emitter Followers or a full bridge.

 

[audioguru]

The NTE105 is a VERY old PNP germanium power transistor in a metal case with a bolt stud.

 

[gary350]

The NTE105 is a VERY old PNP germanium power transistor in a metal case with a bolt stud.

YES, I have 2 of them. The old DS501 transistors are collector items. There are several replacements, 2N441, 2N2491, NTE105, M9251, SK3012. These were used in car radios in the 1960s, rated 50v, 15a, 150w.

Will a Mosfet work on 12v?

 

[audioguru]

ANY Mosfet will work on 12V but many speakers will be destroyed or crippled by the DC fed to them in your last circuit (if the transistor is corrected to be an NPN type or an N-channel Mosfet is used). A speaker needs AC (Alternating Current) so that its cone can alternate one way then the other way back and forth.