keron Posted May 27, 2007 Report Posted May 27, 2007 i need an alarm circuit with very loud sound output.i have tried the circuit in attachement but sound output is not good.please help. i used 8ohms 0.5 watts speaker. Quote
audioguru Posted May 27, 2007 Report Posted May 27, 2007 If the supply voltage is more than 6V then you are straining the poor little 555. It is not designed to drive an 8 ohm speaker. A power amplifier with a fairly high supply voltage will drive an 8 ohm speaker loudly.With a 6V supply, the output power of the 555 into an 8 ohm speaker is only about 1/2W.The 10uF output capacitor reduces the output at frequencies less than 10kHz. It will sound like a little squeak. Quote
MP Posted May 27, 2007 Report Posted May 27, 2007 keron,I'm not sure how much sound you require but you could inexpensively add an LM386 after the 555 and before the speaker.MP Quote
keron Posted May 27, 2007 Author Report Posted May 27, 2007 hello MP, thanks for the reply .can you discribe a little more about adding LM 386.a rough estimate of loudness is, I need to hear the alarm clearly at 20meter circumference,can you help Quote
MP Posted May 27, 2007 Report Posted May 27, 2007 For this distance I would recommend a power amp as audioguru has suggested and I recommend a horn instead of a speaker.MP Quote
keron Posted May 27, 2007 Author Report Posted May 27, 2007 thanks .but upto what distance approximately the buzzers work.i should better go for a buzzer than this circuit..for such small gain. Quote
audioguru Posted May 27, 2007 Report Posted May 27, 2007 An LM386 amplifier IC has an output power of only 0.5W into an 8 ohm speaker with the square-wave signal from a 555 oscillator. Exactly the same power as from the 555 directly into the speaker.A piezo beeper like in smoke alarms has a built-in oscillator/driver that automatically tunes itself to the loudest resonance frequency of the piezo and its tuned case. It makes a single frequency.A piezo speaker needs to have an oscillator circuit to drive it. It has a few resonant frequencies that are loud and many frequencies that are not loud. Therefore it makes a poor siren sound.Use a re-entrant horn speaker driven by a power amplifier. Quote
keron Posted May 27, 2007 Author Report Posted May 27, 2007 thank you all.piezo buzzer consumes less power also ,rt?for small distance it is always better to use piezo buzzer.than a siren circuit like the one i made. Quote
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