Is it possible to get a cash register sound from a piezo?

idbruce

Hi Everybody

I am just finishing up two CNC machines. One CNC will manufacture a product for which I have a patent pending and the other will package it. Approximately (hopefully) every three seconds, the first CNC machine should make the completed product, for which I intend to charge a quarter. When the machine is finished making the product, it pushes the product off the work area, down a slide, and into the packaging, making room for the next one. I have added a piezo siren to the machine for an audible indication of machine error, however, I would also like to use this siren if at all possible to show off just a little. When the product exits the work area, as it slides down into the packaging, I would like the piezo to play a cash register sound. Of course it would be a runtime option, because I know it would be annoying at forty thousand units a day

Is it possible?

Bruce

Cluso99

idbruce: It sounds like you have a piezo that has it's own internal oscillator (a buzzer). There are piezo speakers (used in old modems, Christmas Cards, etc) which could do this but you would require an amplifier and obviously the simple audio circuit, plus a sound file.

Congratulations on your products. I presume since you have asked here, you have a prop in the machines???

LoopyByteloose

I would take a good look at the power rating of the output for piezo. They really aren't much - a small fraction of a watt. I have decided that anything I want to do with sound should have at least 1 watt so I can hear it at a distance. The easiest thing to do is to drive a TIP120 into an 8 ohm speaker of 1 or many more watts, but be sure to limit the base with a 5K pot or you may toast the speaker.

If it doesn't provide the audio quality you desire, you can consider filtering circuitry after you get enough power. I realize this all rather crude to an audiophile that wants a true sinewave at 0.1THD, but it is worth a try.

Of course, the other alternative is to feed a signal into a computer speaker pair that provides the amplification. Several circuits are available that attempt to clean up the square wave before it is amplified.

Cluso99

I used the LM386 with the additional RC circuit to boost the gain in modems of the 80's & 90's. However, they were not all that loud if you remember modems of those days. BUT they are speaker piezos and not buzzer piezos - they are completely different things!

Toby Seckshund

The responce of a piezo element would be too resonant to give a true rendition of a cash register. The only reason that they achieve such volumes, for input power, is because of this resonance.

Piezo tweeters are not much better, I hate them (and I'm half deaf).

idbruce

I thank you all for your replies.

I did not think a piezo could handle it, but I thought I would check with the experts just to make sure. After reading your comments, I started searching for a suitable solution to my needs and desires. As previously mentioned, I need an audible indicator of machine error. The audible indicator does not have to be very loud and I believe the piezo will suit my needs. As for the cash register sound, I just want it to be faint enough to hear, but I want to be able to hear the sound crystal clear. First I looked at some old PC tweeters I had laying around, then I tore apart a telephone, and then it finally dawned on me that a headphone speaker would be the perfect solution.

I know that wav files can be saved in EEPROM, and I already have the cash register wav file. Now I just need to interface the headphone speaker to the propeller chip. Although it is not a complete solution yet, my partial solution is to have two sound outputs, one for machine error, and the other to play wave files.

Thanks for your comments.

Bruce