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newbie SPL meter harware hacking

Former Member

Hello fellows,

I am a newbie electronic hobbyist. I am currently working on one arduino spl project. I need to connect an spl meter to an arduino and control a servo motor based on sound pressure detected by spl meter. First I was planning to create an spl meter using arduino but the spl meter that i created was not fast and accurate, since I didnt have much time to work on it I decided to buy a separate, cheap SPL meter and connect it to my arduino. However, I have never done any hardware hacking before, and since there is NO schematics for digital spl meter (specially the model that i own ) I have NO CLUE where is the SPL meter's out put. I have stared hours on circuit tring to find out how I can connect my SPL meter to arduino.  my initial though was maybe there is a data LCD pin that can help me. but I was wrong! I have uploaded the SPL board pictures too. It is Hobbyking Digital Sound Level (dB) Meter.

ANY IDEA? SUGGESTION?

 

 

ALSO, out of curiosity, meter's LCD is really weird to me. there is no pins on LCD, do you know what kind of LDC is that? (pictures uploaded). It is like a glass attached to the board through a plastic, but there is no pins on it!

 

 

thanks

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  • Hello Jame,

     

    if you are still working on this I might be able to help. Due to E14's slightly odd way of hiding things I only blundered into you post today.

     

    I'm sorry to say that you've picked a difficult device to hack into - was it cheap - it's surprsingly complex.

     

    The LCD connects though the plastic to the row of pads on the pcb  - the magic is that the plastic contains conducting threads which run from top to bottom but not sideways and are insulated from each other. The threads are much smaller than the pcb pads so if you just sandwich the plastic between two rows of pads which are roughly alligned they end up connected. The LCD will have a row of pads which might be very hard to see.

    You could pick up signals from the LCD driver chip (on the row of pads) but they will be very hard to decode and may not be simply digital (there aren't many pads so the LCD drive will probably be multiplexed which involves multiple voltage levels).

     

    It might be easier just to build a sound level front end for the Arduino.

     

    MK

  • in reply to michaelkellett

    Hello ,

    Very cool info about LCD. I never knew that.

    And after some time of probing using meter, I could get some readings from of the the outputs in one of the op amps. And now, as you recommended I thinking to buid an stand alone SPL meter to hook it up to an arduino (if I succeed). image

    Thanks for reply.

  • in reply to Former Member

    I'm not sure how experienced you are at building circuits but you might find the Analog devices AD8307 is a good part to use. You can make a wide range sound level meter with one chip using this part. It is a bit expensive (about £11).

     

    Look at fig. 44 on the datasheet.

     

    I doubt if this part will work on breadboard so you would need to make or perhaps buy a pcb.

     

    http://www.analog.com/en/rfif-components/detectors/ad8307/products/product.html

     

    Ask again if you fancy trying this part and need some more info.

     

    MK

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