Need to make project louder

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rrch123

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Hi all!
I was building this project for an "anti-dog device":
**broken link removed**
http://www.zen22142.zen.co.uk/Circuits/Misc/whistle.htm

This device works nicely, but I need it to be louder. We are using it for our dogs whenever we drive into our driveway and they like to play right infront of our tires. We are afraid that we might hit one, and we need the ultrasonic sound to be louder because the dogs cannot hear it over the trucks roar.
I am a complete newbie at electronics in general, and can only really read schematics at this point to put together projects. Any help anyone can give me would be great.
Thanks
rrch123
 
Piezo's require quite large voltages to produce maximum output. First, try running the 555 off of 15v or so, so that it produces the highest voltage swing it can. If you still have too low a level, you might try an LT44 mini audio transformer (1k-20k). Connect the 1k winding where the piezo currently is and the 20k to the piezo. It is also good to place the sounder in a tuned cavity to utilise standing waves to increase the sound level acoustically, but I can't calculate the size needed sorry, experiment with it!
 
You could also consider adding an inverter to the ground pin of the piezo, this will double the voltage and quadruple the power.
 
Have you tried using the cars battery, it will get you about 14 volts when
the car is running. Use that to run it over the 9VDC?

The inverter will work as well, so long as the piezo can handle it.
 
Place a small piece of plastic pipe around the piezo, blocking the rear end. Face the open end towards the problem dogs.
 
Thanks too all! I will try all your suggestions to see which, or if some together will work the best.
 
I really don't understand this use of invertor to increase output. It makes sense with bipolar supplies and bridged amplifiers, but with a unipolar supply (of say 15v) the most you will ever get accross a component is 15v, which is exactly what you get without the invertor? Am I missing something?
 
Without the inverter you only get 7.5V peak, with an inverter you get 15V. Bridged amplifiers always use a single supply, thats the whole point, you get double the voltage output hence four times the power and only require a single supply.
 
If I connect a 555 (or more to the point CMOS7555) to a 15v supply, the output viewed on a scope swings between ground and 15v, adding an invertor would achieve the same voltage swing? Is this something to do with the capacitor then?
 
Dr.EM said:
If I connect a 555 (or more to the point CMOS7555) to a 15v supply, the output viewed on a scope swings between ground and 15v, adding an invertor would achieve the same voltage swing? Is this something to do with the capacitor then?
Click to expand...
The output of a Cmos 555 or a Cmos inverter swings the full supply voltage without a load. A load draws current which causes a voltage drop across the output's internal resistance and reduces the output voltage swing.

With a 12V supply, a Cmos 555's output can sink 8mA with typically a 0.3V loss or 50mA with a 1V loss. It can source 10mA with typically a 0.7V loss.

Look up the loss of a Cmos CD4049 buffer/inverter yourself.

What capacitor?
 
mshemyalnisar said:
why cant a simple BJT amplifier circuit be attached instead???
Click to expand...
You can use any kind of inverter circuit you want. A transistor amplifier can supply a high output current but has a voltage loss. A piezo transducer doesn't draw much current and needs voltage which is best provided by Cmos.
 
Thats what I thought, the piezo needs very little current and so it can be supplied with the full voltage output by a CMOS 555 directly with no issue? I'm still not understanding the use of an invertor to supposedly supply more voltage? More current is possible but isn't required, and more voltage is possible by increasing the supply, or with a transformer like I mentioned earlier. And as I also said earlier, a cavity will increase the level, but finding the resonance is difficult at higher than audio frequencies (doing it by ear is very effective otherwise).
 
The Cmos 555 has a max supply voltage of only 15V and 12V max is recommended. With 12V its output swing to a piezo is about 10Vp-p.
A piezo needs about 24Vp-p to be loud.
If an inverter drives one wire of the piezo then it is driven by a bridge with about 20Vp-p.
 
This is what I don't understand. How does driving it with an invertor (i'm assuming running from the same supply line, +12 and gnd) make a 20v swing? Sure, if the invertor ran off of effectively -12v and gnd then yes, it could be. But using the existing supplies I just don't see that it can be. Were you thinking using different supplies all along?
 
Dr.EM said:
This is what I don't understand.
Click to expand...
The output of the Cmos 555 is 10Vp-p. If the other end of the piezo is grounded then it gets 10Vp-p.
The output of a buffer inverter is also 10Vp-p but its phase is the opposite to the output of the Cmos 555 so the piezo gets 20Vp-p.

Exactly the same as how a bridged car amplifier works to double the voltage across a speaker and get almost 4 times the power into it.
 
I understandand bridging, as it uses bipolar supplies and so instead of being between ground and 12v, it can have as much as between -12v and +12v. However, is an invertor runs off of the SAME gnd and +v, how is it it can produce 20v then? You must be thinking of adding in a -12v rail? Or is this some effect intoduced by using the coupling capacitors? I know they can produce voltages different to the supplies on the other side.
 
I still do not understand how it works either but it does. I figure capacitance.

Nigel and RonH helped me on a project a long time ago, telling me remove the grounded side of an output I had a square wave on (IO pin and ground) and move the grounded side to an IO pin and invert it (was on a microcontroller).. I went "that can not work".

Changed it, got out the scope.. My 6VDC battery project was doing a 12VDC square wave p-p..

I have used it on piezos as well to make them louder.

Later I found out a "Nigel Goodwin" was wrote up in a magazine for making a piezo louder and not adding parts to a PIC circuit. It works.
 
Dr.EM said:
I understandand bridging, as it uses bipolar supplies and so instead of being between ground and 12v, it can have as much as between -12v and +12v.
Click to expand...
Most bridged amplifiers do not use bipolar supplies. Bridged car amps operate directly from the 12V battery and each end of the speaker gets nearly 11Vp-p for a total of 22Vp-p across it for nearly 15W at clipping into a 4 ohm speaker. Without bridging only one end of the speaker will get nearly 11Vp-p for only 3.8W at clipping.
 
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