I've seen in this datasheet of this project and it requires 2 buzzers, a 16 ohms and a 140 ohms. The problem is that I cant find these buzzers in my local shop. I've also found that the buzzers come in different voltajes so idk which voltaje should i get for these resistances or if there is something that I dont know about shopping buzzers.

 

What exactly is this project? The LM386 is an old, very old power amplifier which has a fixed gain of 20. While gain can be changed it is normally 20. The LM 386 is designed for low voltage amplification projects As drawn it appears the input "buzzer" is likely a piezo buzzer used as a microphone while the second one serves as a speaker. This is the LM 386 Data Sheet and if you look at applications you will see the amplifier configured for gain of 20 and a gain of 200 which are both very common LM 386 circuits and have a resemblance to your schematic. Thus a link to where you found the circuit and your goal would help.

Ron

 

What exactly is this project? The LM386 is an old, very old power amplifier which has a fixed gain of 20. While gain can be changed it is normally 20. The LM 386 is designed for low voltage amplification projects As drawn it appears the input "buzzer" is likely a piezo buzzer used as a microphone while the second one serves as a speaker. This is the LM 386 Data Sheet and if you look at applications you will see the amplifier configured for gain of 20 and a gain of 200 which are both very common LM 386 circuits and have a resemblance to your schematic. Thus a link to where you found the circuit and your goal would help.

Ron

Hi, thanks for answering. The project is an e-bow, it's a device used on guitars. When you approach it to the guitar's strings, the buzzers make the string vibrate, the vibration of the string is capted by the guitar pickup and make the sound. In conclusion, the buzzers doesn't make a sound nor work as a microphone, just make the string vibrate. You can check it on youtube if you still not undertanding how it works.
About the lm386, the only projects that I've found on the internet used this IC.

in this video you can see the project

and in this one how it works.

 

That is really slick and I think I know what they are doing. They use that word "buzzer" which is deceiving What they are is actually piezo transducers. Piezo elements come in handy when you need to detect vibration or a knock. You can use these for tap or knock sensors pretty easily by reading the voltage on the output. They can also be used for a very small audio transducer such as a buzzer. Actually the unit on the left is an input and the unit on the right is an output. I am not sure what the specified those resistance numbers but just about any cheap piezo transducer should work. They typically cost about $1.50. Here is an example using about the same circuit.



Note in this example how they used a telephone pickup coil and for the output hacked a small audio transformer. The out is likely more tricky than the in and my read on these little gizmos is they require some tweaking and playing around with to get good results. I did notice in the one video how the guy was hacking apart the buzzer used on the output side. My guess is any number of piezo transducers will work on the input including those from Spark Fun depending on your location. For the output I would chop down a small typical audio output transformer. You want one with a 600 Ohm input and then you cut out the secondary. This is why the reference to E core as when you are done the transformer core looks like a letter E.

Hopefully another member will come along with some better thoughts.

Ron

 

That is really slick and I think I know what they are doing. They use that word "buzzer" which is deceiving What they are is actually piezo transducers. Piezo elements come in handy when you need to detect vibration or a knock. You can use these for tap or knock sensors pretty easily by reading the voltage on the output. They can also be used for a very small audio transducer such as a buzzer. Actually the unit on the left is an input and the unit on the right is an output. I am not sure what the specified those resistance numbers but just about any cheap piezo transducer should work. They typically cost about $1.50. Here is an example using about the same circuit.

View attachment 141995

Note in this example how they used a telephone pickup coil and for the output hacked a small audio transformer. The out is likely more tricky than the in and my read on these little gizmos is they require some tweaking and playing around with to get good results. I did notice in the one video how the guy was hacking apart the buzzer used on the output side. My guess is any number of piezo transducers will work on the input including those from Spark Fun depending on your location. For the output I would chop down a small typical audio output transformer. You want one with a 600 Ohm input and then you cut out the secondary. This is why the reference to E core as when you are done the transformer core looks like a letter E.

Hopefully another member will come along with some better thoughts.

Ron

So you mean that I can use any piezo transducer for the input (with or without hacking it?) and for the output I dont know what is an audio output transformer, so if you could explain that a bit clearer would be great.
About these piezo transducers I only know the disks and I'm not sure if they would work (I dont have a great knowledge of electronics too).
Also, if you know, could you specificate which model/parameters should I consider to buy them.

 

The devices in the video are electromagnetic, not piezo. They are small speakers. Small speakers like this are used in devices where the system needs to beep at specific notes, as opposed to a piezo beeper that works best only at its self-resonant frequency. The one on the input is acting as a dynamic mic. The higher impedance comes from more turns of finer wire, so the output voltage is greater than that of a lower impedance part.

The circuit is a non-inverting audio amplifier. The two transducers are located to *intentionally* create positive feedback. The output speaker rattles the string, the string rattles the input microphone, the 386 amplifies it and sends it back out to the string. And around, and around. The amp is fairly wideband, so the system will oscillate at whatever the resonant frequency of the string is.

Using a modified audio transformer for the output suggests that the coupling between the output transducer and the string is magnetic, rather than acoustic. In the same way, I suppose the input transducer could be acting as a magnetic pickup rather than acoustic. Either way, the intentional positive feedback that auto-tunes to the string frequency is VERY clever.

ak

 

Thank you analog.

Ron

 

I found this using Google. https://www.digikey.com/product-det...tor&utm_campaign=ihstest&source=Datasheets360

 

The devices in the video are electromagnetic, not piezo. They are small speakers. Small speakers like this are used in devices where the system needs to beep at specific notes, as opposed to a piezo beeper that works best only at its self-resonant frequency. The one on the input is acting as a dynamic mic. The higher impedance comes from more turns of finer wire, so the output voltage is greater than that of a lower impedance part.

The circuit is a non-inverting audio amplifier. The two transducers are located to *intentionally* create positive feedback. The output speaker rattles the string, the string rattles the input microphone, the 386 amplifies it and sends it back out to the string. And around, and around. The amp is fairly wideband, so the system will oscillate at whatever the resonant frequency of the string is.

Using a modified audio transformer for the output suggests that the coupling between the output transducer and the string is magnetic, rather than acoustic. In the same way, I suppose the input transducer could be acting as a magnetic pickup rather than acoustic. Either way, the intentional positive feedback that auto-tunes to the string frequency is VERY clever.

ak

I've been around these with various guitar players in years past, but long before I knew anything about electronics. I'm almost positive that you're right about it being all magnetic, not acoustic, at least in the commercial e-bows. They're really fun!

The average guitarist will just use them as a silly novelty and quickly wear out the charm, but with a little practice and a lot of taste they can be truly amazing and beautiful!

 

I've seen in this datasheet of this project and it requires 2 buzzers, a 16 ohms and a 140 ohms. The problem is that I cant find these buzzers in my local shop. I've also found that the buzzers come in different voltajes so idk which voltaje should i get for these resistances or if there is something that I dont know about shopping buzzers.

Edit: This device works with opened polarized electromagnetic system. Distance between string and pole 5 is about 1 mm for both buzzers.