Ultrasonic speaker or ??

[audioguru]

Your meter is made to measure 50Hz and 60Hz. It will be very wrong when measuring your high frequencies.

If you bought piezo tweeters that have a manufacturer's name and a detailed datasheet then you could calculate the current through the reactance of their capacitance at any frequency.

The datasheet of every 555 shows a graph and a calculation for its oscillator frequency.

 

[MrDEB]

No real data sheet except what is posted on the website link for tweeter.
What method can I use to determine the current draw?
will remove output cap.

 

[audioguru]

Without a datasheet, you don't know what is the loudness of your cheap piezo tweeters at each frequency (the frequency response of a piezo tweeter goes up in peaks and down in notches at certain frequencies). You don't even know at what distance the loudness is rated. 10cm? 1m?
Current doesn't mean much since a piezo transducer is driven and has its loudness rated by its signal voltage, not current and not power.

A piezo tweeter has its loudness rated by the amount of voltage that would be across a normal coil and magnet tweeter at a certain power. Then you calculate the signal voltage.

 

[MrDEB]

So I shouldn't be concerned as to how much current drain the tweeter is drawing seeing how the voltage is only 9v but when connected to a PIC it will only be 5v.
Thought about inserting a transistor on output of 555 or PIC so the 555 or PIC has less current drain.
For automotive app the amplifier we discussed eairler in this thread will be utilized.

 

[MrDEB]

something along this example

here is what I am thinking as the amp when used will need some resistance and the transistor will reduce the current drain on the PIC output?

 

[audioguru]

Piezo tweeters are driven with voltage, not current. Your transistor has a lot of current but nearly no voltage and will cause a very low level of sound.
The piezo tweeter has a max "power" (if an 8 ohm coil and magnet speaker is used) of 50W which is a voltage of 56.6V p-p. Your transistor might have an output as high as 3V p-p.

Amplifiers are push-pull. Most of their power goes to the speaker. Your transistor wastes half of its power heating the 10 ohm resistor.

 

[MrDEB]

then just connect as per this schematic?
**broken link removed**
looks pretty easy but will the 555 or a PIC actually drive the tweeter?

 

[audioguru]

The 555 in the "Dog Whistle" has an output of 6.9V p-p which is 2.45V RMS when the 9V battery is brand new. Then its effective power into 8 ohms is only 0.75W so the piezo will not be very loud.

The loudest peak frequencies from your piezo tweeters is 94dB probably at a distance of 1m and probably with an effective amplifier power of 1W into 8 ohms so your tweeter fed from the 555 circuit will have an output of about 92.5dB at 1m, 86.5dB at 2m and only 80.5dB (not loud) at 4m. Other frequencies will have much less output.
The output level from a PIC is less.

I think the Dog Whistle is used when the dog is nearby.

 

[MrDEB]

stupid idea or not

To put a load on the amp what about putting an 8ohm speaker in series w/ piezo tweeter?

 

[Nigel Goodwin]

To put a load on the amp what about putting an 8ohm speaker in series w/ piezo tweeter?

Yes, a stupid idea (in every respect), why would you want to do that?.

Assuming there was any valid reason for adding an extra load (and there aren't really), you would put it in parallel with the piezo.

 

[MrDEB]

I thought about parallel but then it was mentioned to add a 5 watt 2-10ohm resistor in series with the piezo tweeter.(LM4950 amp or the TDA1518BQ, what ever I can get. Don't want alot of volume. Deer can hear up to one mile away.
This was just a thought. I come up with crazy ideas now and then You never know unless you ask questions.
Now to maybe put 2 piezo tweeters in parallel using a BTL amp. Thought about going stereo with one set of frequencies per tweeter (2-8Khz and 15-2oKhz)
That will surly scare them deer!.
LOOK OUT WILDLIFE, MrDEB is wanting to scare the hide off of you.

 

[Nigel Goodwin]

I thought about parallel but then it was mentioned to add a 5 watt 2-10ohm resistor in series with the piezo tweeter.(LM4950 amp or the TDA1518BQ, what ever I can get. Don't want alot of volume. Deer can hear up to one mile away.

As we've repeatedly mentioned, high frequencies don't travel very far - and why would a deer be scared of a barely audible noise a few yards away?. For any hope of it to scare deer away you will almost certainly need LOT'S of power.

The resistor is to protect both the amp and the piezo, but as you're only using low powers it's probably not needed.

This was just a thought. I come up with crazy ideas now and then You never know unless you ask questions.
Now to maybe put 2 piezo tweeters in parallel using a BTL amp. Thought about going stereo with one set of frequencies per tweeter (2-8Khz and 15-2oKhz)
That will surly scare them deer!.
LOOK OUT WILDLIFE, MrDEB is wanting to scare the hide off of you.

I'm highly dubious

 

[MrDEB]

Perhaps connect the ultrasonic frequencies using a high power amp and audiable frequencies into an 8 ohm speaker.
will look at chip amps for more power, like 40 watts? just for the 15-20khz frequencies.

 

[MrDEB]

here is MORE power!
https://www.electro-tech-online.com/custompdfs/2010/04/G15420.pdf
just put a volume control on the one channel (2-8KHZ frequencies)

 

[audioguru]

The "high power" TDA8560 audio amp you found is obsolete and is not made anymore.
It has exactly the same 4W per channel into 8 ohms at clipping with a 13.2V supply as all the other car radio amp ICs.
Its output voltage swing is also exactly the same as all the other car radio amp ICs. Your tweeters are driven with voltage, not power.

Don't you understand that its "40 Whats output" is only when its speaker is 2 ohms so the current in it is very high (but the current in your tweeters is very low), and when its distortion is a horrible-sounding square-wave so the extra harmonics (but not produced by your tweeters) add to its output power, and when its power supply voltage is very high at 14.4V which makes the IC very hot.

The deer will laugh and say, "What is that little sound?" They might be attracted and go to see, SMACK!

 

[MrDEB]

ANY solutions to increase the POWER output of the tweeters?
Thats why I thought of connecting in series from Vdd to tweeter to transistor to ground as per LT Spice diagram I posted. see post 65
the 10 ohm resistor is supposed to be the tweeter.

 

[audioguru]

Post #65 shows a 10 ohm resistor as a heater. A speaker would burn up with that much continuous current in it.
But a piezo tweeter has no resistance because it is actually a capacitor so the transistor "amplifier" will not work.
A push-pull audio amplifier with enough output voltage swing (from enough supply voltage) will work.

An amplifier that produces 50 Watts (not Whats) into 8 ohms has an output of 20V RMS which is 56.6V p-p and needs a 60V or higher power supply. A bridged amplifier that produces 50 Watts into 8 ohms needs a power supply that is 30V or higher. You won't get 60V nor 30V from a car battery without a voltage stepup circuit.

 

[MrDEB]

I guess i'm back to a push pull amp BUT am assuming that a 12-14v automotive supply won't be enought to power the tweeters?
Am really lost? One can buy a 200 watt amp for a car with no real problems??
I recall a push pull amp schematic that uses 4 transistors. Will locate?

 

[mneary]

One can buy a 200W power amp for a car because they contain inverters that generate the necessary 60V or higher power supply.

 

[Nigel Goodwin]

I guess i'm back to a push pull amp BUT am assuming that a 12-14v automotive supply won't be enought to power the tweeters?
Am really lost? One can buy a 200 watt amp for a car with no real problems??
I recall a push pull amp schematic that uses 4 transistors. Will locate?

Even so the maximum power off 12V is only 16W for a bridged amp.

As mneary pointed out, to get high powers in a car you need an amplifier with an inverter built-it, these produce decent supply rails to feed a good size amplifier. However, you do need to be aware that in-car amps commonly GREATLY exaggerate their output powers, you need to look for RMS continuous output per channel.