Help with Sound Level Meter (A weighted) project

Discussion in 'The Projects Forum' started by Mick84, Feb 8, 2015.

  1. Mick84

    Thread Starter New Member

    Feb 8, 2015
    12
    0
    Hello,

    Project time. Im trying to make an existing Arduino sound sensing circuit have it's mic signal be processed through this A weighting circuit. Im using a regular Electret Condenser mic.

    [​IMG]
    upload_2015-2-8_12-32-20.png
    Im attempting to combine these two circuits but when I do I no longer get any response from my LEDs.

    I have used the breadboard cct IC output from Pin 5 as my Input to the filter cct, and the Output of the filter cct as the new Arduino A5 (bottom right) Input.

    I am reading 2.4V at Arduino A5 whether I use the bottom cct on its own or add in the A weighting cct as described? I therfore take it my filter cct is delivering an ouput.

    I have read that Impedance matching is not my most likely problem at the Audio Frequencies (low power) concerned.

    I do not have a spectrum analyser. I have perhaps been over ambitious given my basic Electronic knowledge.
    Any help would be much appreciated.

    Please be brutally honest what you think!!
     
  2. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    If your Electret Condenser mic is directly across Input and Ground of your amplifier I don't see where the mic would be powered? Electoret microphones need powered. Also, what are U1 and U2 and how are they powered? Single or dual supply as in (+) 0 (-) supply?

    Ron
     
  3. Mick84

    Thread Starter New Member

    Feb 8, 2015
    12
    0
    Thanks for taking a look Ron.

    Just to clarify the two pictures shown are completely seperate circuits. I'm trying to make the top one compliment the bottom as it is an A weighted signal that I am trying to achieve as the input into the Arduino.

    Therefore, I have the mic powered as per the bottom drawing (one with the arduino on) from a 5V dc rail via a 22K resistor and on through a LM 386N-1. From this amp I feed it's output to the Input of the A weighting circuit instead of into the Arduino (as per the bottom cct in use on its own)

    U1 and U2 are both NE5534AP 's both powered via 5V dc for +Vcc and via Ground for -Vcc (Pins 7 and 4 respectively)

    Having double checked and since corrected the power inputs to these chips I now have all LEDs illuminated hence I think that I am possibly over amplifying my original mic signal?

    What is the best way to reduce amplitude in terms of the circuitry around the NE5534AP's to see if this cures this?? Do I have too many amplifier stages for what Im trying to achieve? The pot I have for controlling mic sensitivity isnt making any difference. Do I need to alter the amp gains???
     
  4. Magician

    New Member

    Aug 18, 2014
    13
    6
    You can't feed analog input of the arduino with AC at risk to damage a board. Your option: insert two resistor plus cap bias circuits after U2, or better use rail-to-rail single power +5V OPA. With some limitations you can use LM358 or LM324.
    An example, change resistor to 10k both:
    http://wa5znu.org/2011/07/cascata/schematic.jpg
     
  5. Mick84

    Thread Starter New Member

    Feb 8, 2015
    12
    0
    It's a DC circuit ran off a typical breadboard set up with 5V and GND both tapped off the Arduino Uno itself....
     
  6. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Sounds like you just need to drop the amplification at the output stage of your a-weighting circuit. I think you can replace the 5.6k resistor and 10k pot on the output amp with a simple wire from output to inverting input (same config as on input amp) to get unity gain on output.

    That idea might be overkill. You could also try decreasing the 5.6k value and/or increasing the trim pot value to split the difference and get lower, non-unity gains.
     
  7. Magician

    New Member

    Aug 18, 2014
    13
    6
    NE5534 minimum power supply voltage is +-3 V. You have 2.5V at the best.
    Circuits shown above is for dual supply, and it isn't gonna to work. Find another circuits for single power.
     
    Reloadron, Mick84 and ebeowulf17 like this.
  8. ebeowulf17

    Active Member

    Aug 12, 2014
    678
    79
    Good call, Magician. I should've seen that before chiming in.
     
    Mick84 likes this.
  9. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    The circuit that you tried to used, almost no amplifying function whatever U1 just a voltage follower that is to isolation the circuit for two sides, and the gain of U2 only 1.56, maybe it is too less when the signal through a filter.

    I'm not sure the original circuit is suits your need or not, but the circuit was designed for the powered by ±9V~15V, the original circuit is here A-Weighting Filter For Audio Measurements.

    The ADC of arduino only provide the +V, then the circuit you used should be cut off the negative voltage before get into the ADC or using a clamping circuit to shift the voltage from -V~+V moving to 0~+V, and adding a voltage divider to lower the voltage to the ADC acceptable.

    What kind of the function you really need?
     
  10. Magician

    New Member

    Aug 18, 2014
    13
    6
  11. Mick84

    Thread Starter New Member

    Feb 8, 2015
    12
    0
    Thanks Scott. I want to be able to measure 80dB(A) using Arduino as the microcontroller. I have a 5V rail to play with so can't power my Op Amps. I don't have enough circuit knowledge to start again from scratch or to start implementing Single Source Amps as an alternative??
     
  12. Mick84

    Thread Starter New Member

    Feb 8, 2015
    12
    0
    Magician thanks for your input. Unless there is a quick and easy solution to powering the A weight circuit I have either with existing Amps or Single Source alternatives i am going to leave the A weighting out of my Project. By the way its bland close range aircraft noise I intend to measure so Ive read that A weighting aint so important in this instance?

    Mick
     
  13. Magician

    New Member

    Aug 18, 2014
    13
    6
    If it's a question, I have no idea. At least, you explain what you measure in reply #12
     
  14. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    What I don't understand is that if you just want to measure 80dB(A) then why you want to using the weighting circuit?
     
  15. Mick84

    Thread Starter New Member

    Feb 8, 2015
    12
    0
    Because as I understand it you cant convert from dB to dB(A) mathematically
     
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