A sensor which can measure the vibration of a material.

Discussion in 'General Electronics Chat' started by goutham1995, May 18, 2018.

  1. goutham1995

    Thread Starter Member

    Feb 18, 2018
    59
    2
    I am planning on making a musical instrument where I require the conversion of vibration of a material to voltage. The idea is to make a percussion instrument where I hit a plate made of a certain type of material. Based on the different areas on which I hit the plate, the vibrations will be different and after converting the vibrations to voltage, I will take the FFT of the signals to differentiate the different areas on which I hit the material and map it to produce a particular sound. I know that piezoelectric sensor is a material which converts pressure to voltage but I am not sure if it will be robust enough. Is there any alternative I can use?
     
  2. WBahn

    Moderator

    Mar 31, 2012
    22,752
    6,778
    Strain gauges and accelerometers come to mind.
     
  3. danadak

    Well-Known Member

    Mar 10, 2018
    1,228
    253
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    8,474
    1,922
    A piezo disc transducer should be robust enough, unless you are hitting the plate with a sledge-hammer.
     
  5. goutham1995

    Thread Starter Member

    Feb 18, 2018
    59
    2
    Cool. Another thing I have in my mind is to use a seismometer which prompts me to ask a question. What is a seismometer sensor made up of? If it is a made of piezoelectric material, then that's of no use. If it can help in distinguishing vibrations better, it will be useful.
     
  6. goutham1995

    Thread Starter Member

    Feb 18, 2018
    59
    2
    Really? That's great. I will have to test it though and get back to you.Robust in the sense that it should be able to distinguish between the hits in different areas of the plate.
     
  7. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    3,904
    5,227
  8. RichardO

    Senior Member

    May 4, 2013
    2,207
    853
    Imagine a permanent magnet speaker where the cone is replaced by a weight. The movement of the weight moves the speaker coil inside the field of the magnet producing a voltage.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,843
    519
    A seismometer is like a speaker with a heavy voice coil .I used one to detect hits on a paper target; 64 ohm VC, 1/4 W, 1.5 in. dia. with 1/2 X 1/2 thin wall Al tubing cemented to VC. Another uses a 17 mm piezo disc on a 20 mm brass disc with a dead LR41 battery cemented to center. Whole thing cemented to a 2 mm X 30 mm plastic disc with a 18 mm hole in center. Works well with paper target ; could mount it to your plate with 2 narrow strips of double faced adhesive tape.
    Does it not work with a microphone and amp. ?
    Are you making a steel drum ?
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,843
    519
    Using my piezo geophone attached to Al plate with alligator clip, measured 8 V PP, 250 Hz fundamental with lots of harmonics which tapered off to 0 V in about 40 msec. when taped with a wood stick. Plate was suspended with rubber bands.
     
  11. Reloadron

    Distinguished Member

    Jan 15, 2015
    3,299
    1,453
    That would be my thinking but using an accelerometer and a single axis accelerometer. The type used for acoustic testing. You would choose one for a specific G force range and frequency response. Here are a few examples. There are likely a dozen manufacturers who make this type.

    Also as mentioned Piezoelectric accelerometers are well suited for what you want to do and are inexpensive so it really depends on what you plan to spend and to what uncertainty you want the measurements?

    Ron
     
  12. MisterBill2

    Active Member

    Jan 23, 2018
    894
    163
    I worked on a research project that was for a sensor that measured higher frequency vibration of steel materials. .Depending on the degree of accuracy that you want, there are quite a few choices. But the highest output will indeed come from a PZT transducer disk. These are available from many different sources and won''t cost much. But you do need to insulate the disk from the plate. Have fun experimenting. I certainly did!!
     
  13. ArakelTheDragon

    Active Member

    Nov 18, 2016
    639
    28
    A piezo crystal is used for such things normally, but I do not know the exact type. However your problem does not come from the crystal alone, it comes from the audio amplifier after it, which needs to be very good for this purpose. Normally this is used for air instruments (like a clarinet which has a microphone at the end). But this is specialized audio electronics, so be prepared for testing and failure, or find someone who knows what he is doing.
     
  14. Reloadron

    Distinguished Member

    Jan 15, 2015
    3,299
    1,453
    Thinking about this a little more what you are describing is along the lines of what I always called a steel drum or steel pan. Anyone who has enjoyed the sounds of a steel band knows how amazing the instruments sound, especially considering most were hand fashioned from 55 gallon drums.

    A good accelerometer will be plenty robust enough. Again I am speaking about accelerometers similar to those pictured below which come in a wide range of mounting configurations and shapes and sizes.

    Accel2.jpg

    You may want to give Signal Conditioning Piezoelectric Sensors a read through. Place some emphasis on charge amplification. So you start with a sensor and then work your amplification scheme and then worry about your FFT or whatever you wish to do with the data.

    Ron
     
  15. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    2,150
    473
    Any material will vibrate dependent on its hardness and physical dimensions. You'll find this true if you take a steel pipe and bang on it in different locations. You'll still get the same frequency. Tone may change a little but the vibrations are going to be reactive to the size, shape and hardness of the material.

    Sounding like you want to make something like those steel drums you hear in typically Caribbean style music. Those steel drums start out as simple steel drums. The metal bottom is pounded in different places to thin out the materials and cause different stress levels within the steel, which is why you see them rapping on the drum in different locations causing different tones. But just where you strike a steel drum is a product of where you stressed the steel by stretching it through impact. It takes a while to get one into the right tune, and I don't think they retain their tuning very long. Once they lose their tune I don't think they can be restored. Maybe changed to lower frequencies or something, I'm not the expert on those things. But what you're asking to do will certainly be a challenge.

    I've played drums. And drums come with symbols. Depending on how I struck them they'd respond lightly or with a crash. But they always produced the same tone. Except for the bubble shape at the top, called "the bell". Even then, if you listen close to the tone you still hear the same resonant frequency.

    As for converting vibrations into musical notes, an electric guitar does it with a magnet and a coil of wire. The magnet sits still within the coil. When the steel string is plucked it changes the magnetic field, causing a small voltage in the coil. That voltage is picked up and amplified. However, you can trick the string into double vibrating (that's what I'm calling it, don't know if it's a correct term) where you touch the string in a location where the string will actually simulate a sine wave, half of the string swinging (lets call it) left while the opposite end of the string swings right. Still, it's a resonant frequency of the string.

    I want to watch this thread to see if you make any progress on your project. I'm curious to see how this turns out.
     
    goutham1995 likes this.
  16. goutham1995

    Thread Starter Member

    Feb 18, 2018
    59
    2
    I'm making an electronic version of an Indian classical musical instrument called Mridangam.
    https://www.google.co.in/search?q=m...69i57j35i39.3549j0j7&sourceid=chrome&ie=UTF-8
     
  17. MisterBill2

    Active Member

    Jan 23, 2018
    894
    163
    You will discover that the signal from the string vibration is quite different from the signal from the body vibration. Just consider the electric guitar as an example of that. So here is a suggestion for a means of converting the vibration of the instrument body into an electrical signal. Find an old phonograph cartridge, a crystal one would be best because of the much higher output voltage. Replace the needle portion with a similar diameter sewing needle, and that will be something that can probe the instrument body until you find the location that gives the sound that you want. You will need to feed the signal from the pickup into a high impedance amplifier input to get the right frequency response.
     
    goutham1995 and Reloadron like this.
Loading...