Will this circuit work?

[audioguru]

1) Use a transistor to make the piezo beeper (with internal oscillator) beep when the transistor is turned on by a flashing LED.
2) The flashing LED might need a series current-limiting resistor.
3) The transistor will need a bias resistor in series with its base.

 

[Nigel Goodwin]

1) Use a transistor to make the piezo beeper (with internal oscillator) beep when the transistor is turned on by a flashing LED.

Why are you assuming he's got a piezo beeper with built-in oscillator, the third style in his pictures is just as commonly a dumb piezo disk as one containing an oscillator (I have them at work).

Easy to tell, just still a battery across it - and try both ways.

 

[audioguru]

He is taking old parts out of old junk. He needs to buy or steal a new piezo beeper that has an internal oscillator.

 

[eTech]

Except for the ones on my range and my furnace.

ak

I gotta agree with AG on this one....blue is kinda strange as a warning color. At least in the USA.

 

[For The Popcorn]

I gotta agree with AG on this one....blue is kinda strange as a warning color. At least in the USA.

That doesn't change the fact that self-flashing blue LEDs exist and are not a rare commodity.

 

[gary350]

Up Date

I connected my 555 timer siren to all 3 of these devices and they all work. The piezo buzzer is not loud with 12v but it might be louder with 30v like it is rated for. The transducer is about 2x louder that piezo and that is nothing much either. None of these have a built in OSC I already knew that from testes I did yesterday. The 1.25" speaker is louder than the other 2 devices and that is not loud either, maybe .01w. My siren has a 2w speaker it hurts my ears from 2 ft away 12.5v with Lithium batteries.

None of these devices are loud enough to be used for anything. Our kitchen microwave oven seems loud enough the piezo buzzer probably operates on 30v like its rated for.

This was educational for me. I learned about transducers and piezo buzzers.

 

[audioguru]

www.digikey.com (or .ca) list 3027 alarms, buzzers and sirens. They say if they are a transducer (a speaker) or a beeper (with an internal oscillator) and each listing has a manfacturer's datasheet.
Most of them are cheap transducers and the beepers with an internal oscillator cost much more.

Powered from only 3V the beepers are not loud.

 

[eTech]

That doesn't change the fact that self-flashing blue LEDs exist and are not a rare commodity.

That's not what I wrote.

 

[Tony Stewart]

Although uncommon, size matters. Acoustic pressure and frequency parameters determine loudness. Yet it is still possible to achieve high levels with 3V although rare and possibly obsolete.

Buzzers Transducer, Externally Driven Piezo 3 V 3mA 2.5kHz 106dB @ 3V, 1cm Custom Wire Leads

This is a LOUD piezo diaphragm that needs a simple CMOS astable oscillator and inverter with a 3V battery.

Similarly, LEDs may be ultra-bright and some flash. but it may be rare to be both ultra-bright and flash. But with specs, custom solutions can easily be achieved.

Random mix and match parts rarely satisfy unspecified requirements.

 

[For The Popcorn]

I got the flashing LEDs and piezo beeper I posted in post #8 (I had to order other parts), and tested the circuit I showed. The results are surprising.

First, I couldn't find any authoritative documentation whether these flashing LEDs need a current limiting resistor. I tested current draw vs voutage. Current draw went up to around 35mA at about 6 volts and remained constant at increasing voltage. Current appears to be internally limited, so no current-limiting resistor is required as it is with conventional LEDs.

The beeper produces ear-shattering noise at as little as 1 volt, with 1 mA current draw.

So what happens when you connect them is series? Disappointment. Apparently the beeper draws so little current that the LED "brain" can't turn on. The beeper sounded continuously and the LED did not illuminate.

 

[Nigel Goodwin]

First, I couldn't find any authoritative documentation whether these flashing LEDs need a current limiting resistor.

Obviously they don't, because they aren't an 'LED', they are an electronic flasher circuit incorporating an LED for it's output, so all the electronics required are in the LED casing, including current regulation.

 

[For The Popcorn]

Not to disagree, but please explain how that is an obvious conclusion based on this or any other flashing LED datasheet.

On this datasheet, it lists Vf and max current, exactly as would be listed for any LED.

 

[Nigel Goodwin]

Those specs are presumably for the internal LED, not the external interface. None of the specs even mention the blinking part, although it's mentioned briefly above the LED spec in (2).

Perhaps you would care to post a cheap circuit for producing a fixed speed flashing LED where brightness is controlled by an external resistor?.

 

[gary350]

Transducer & piezo buzzer both need an osc., they are not loud enough to do what I want.

I have been experiment and this is the circuit I need. The 30 minute 555 timer turns the other 555 time ON/OFF for 1 second every 30 minutes. The other 555 times produces a 1 second BEEP at about 2.5 to 3 KHz. I have a small TV speaker 12v produces a very loud BEEP. Hide this under the living room sofa wife will jump straight up when it blasts out a loud 1 sec BEEP. Next week is Thanksgiving there will be several people in the living room. LOL. One loud BEEP will make every one jump then 30 minutes later they won't be expecting another, BEEP. LOL. Test I did the tiny TV speaker is louder than I expected.

 

[audioguru]

The seller of the blinking LED says it has a built in blinking IC that operates at 1.5Hz.
The forward voltage and brightness of the LED are listed but not the supply voltage for the IC inside the LED.
The maximum current and maximum operating temperature are listed so I think the constant current parts in the IC must be limited to 30mA and 85 degrees C with an external resistor.

 

[audioguru]

An old NE555 or old LM555 eat battery current all the time, even when the timer is simply timing and not powering anything.
Modern Cmos 555 ICs draw almost no battery current when timing but cannot drive enough current into the beeper so a transistor or Mosfet must be driving the beeper.

 

[Nigel Goodwin]

The seller of the blinking LED says it has a built in blinking IC that operates at 1.5Hz.
The forward voltage and brightness of the LED are listed but not the supply voltage for the IC inside the LED.
The maximum current and maximum operating temperature are listed so I think the constant current parts in the IC must be limited to 30mA and 85 degrees C with an external resistor.

Have you ever seen a flashing LED chat has an external resistor? - I'd also like to see what kind of circuit you think would create a fixed speed flashing LED with current set by an external resistor?.

 

[For The Popcorn]

I couldn't find any authoritative documentation whether these flashing LEDs need a current limiting resistor.

Obviously they don't, because they aren't an 'LED', they are an electronic flasher circuit incorporating an LED for it's output, so all the electronics required are in the LED casing, including current regulation.

The maximum current and maximum operating temperature are listed so I think the constant current parts in the IC must be limited to 30mA and 85 degrees C with an external resistor.

Now that this is cleared up.....

I will note that Big Clive, on his "chaos" and "super computer" panels of flashing LEDs, does use (and recommends) a series resistor for each flashing LED.

 

[Nigel Goodwin]

Now that this is cleared up.....

Hardly 'cleared up', one persons suggestion - with no indication of how such a scheme might work in practice.

It's rather bizarre though how there seems to be no mention in the datasheets of their operation?, best I could find on a quick google was:

Flashing LEDs look like ordinary LEDs but they contain an IC (integrated circuit)as well as the LED itself. The IC flashes the LED at a low frequency, for example 3Hz (3 flashes per second).Flashing LEDs are designed to be connected directly to a particular supply voltage such as 5V or 12V without a series resistor.

 

[Tony Stewart]

When you can't make it work, define/focus on your goal. Then a solution is easier. 3 mismatched or random parts do not make a solution.
Unknown requirements are battery, LED, buzzer and life span.
What is the purpose?