Sound activated LED

Discussion in 'General Electronics Chat' started by happs, Mar 16, 2005.

  1. happs

    Thread Starter Member

    Feb 27, 2005
    24
    0
    Hey guys

    I am trying to build some flashing disco lights that react to sound. I am still on the first stage -- the sensor. I have an electret microphone circuit that I built but it is not sensitive enough. I literally have to blow into the mic to make the LED light up. How would I increase the sensitivity of this circuit ? I do have an AUDIO operational amplifier (386) in my tool box but have no idea how to use it (I am using the LM741 atm) so I don't know if that will help. Could someone please give me some pointers or a schematic that will enable me to complete this section of my project.

    I already know how to build the flashing part from what I have learned already.
    This circuit will eventually drive a monostable.

    Here is my schematic (sorry couldn't find the diagram for a microphone so had to use a speaker.)

    [attachmentid=486]

    Thanks in advance for any help :)

    - Happs
     
  2. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    The 741 op-amp is adequate for your purpose, but it does need the transistor to dive the l.e.d.

    The LM386 wouldn't need the transistor but might cost more than the 741 plus transistor - I haven't checked prices.

    Sticking to your original 741 and a transistor, this circuit should be better.
     
  3. happs

    Thread Starter Member

    Feb 27, 2005
    24
    0
    David,

    Thankyou for the information about the 741 and 386. And thankyou even more for the schematic you took time to draw out for me !!! I am really appreciative of your time and expertise. :)

    I'll try out what you suggested and then get back to you either tomorrow or tonight on how it goes :)

    Thanks again

    - Happs
     
  4. happs

    Thread Starter Member

    Feb 27, 2005
    24
    0
    Hey David..

    Works great, thankyou for the help!! Had to make some minor adjustments just so it functioned how I needed it to but your schematic was fantastic! Thankyou!

    - Alex
     
  5. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0

    Great news Alex, thank you for letting me know.
     
  6. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    Just curious David. What do the 2 front side caps do?
     
  7. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    I don't know which caps you mean.
     
  8. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    WHen I said front side, ment if you look at it from left to right. I.e. the cap on the non-inv input and the cap to ground on the feedback loop.
     
  9. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    The one at the input isolates the two d.c. potentials, one across the mic capsule the other set by the two equal value resistors at half the supply voltage.

    Since the non inverting input also needs to be at half the supply voltage the C to zero volts is necessary to isolate the d.c. in the feedback loop - otherwise the output of the amplifier would go to the positive rail in an impossible attempt to achieve this.
     
  10. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    Thank you very much.

    Couple more questions, (never seen a circuit like that before with the caps)

    The feedback look amplified the hell out of the ac portion of the signal, but attentuations the DC since the feedback loop doesn't complete the DC circuit?

    Amplification same as a typical non-inverting?

    Whats the cut off frequency assuming the 741 is ideal?
     
  11. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    The voltage gain through the op-amp is given by 1+Rf/Rin, i.e. 101 in this case.

    The d.c. in the feedback path isn't attenuated, it is just isolated from the zero volts line.

    The lower -3dB point is at around 40Hz. (Where the reactance of the isolating C in the feedback loop gets to around 400 ohms.)

    Gain bandwidth product is 1MHz, so it will roll off from 100 at 10kHz.
     
  12. happs

    Thread Starter Member

    Feb 27, 2005
    24
    0
    Hey :D

    Ok here is what I made in the end from what I have learned.
    It's a sound activated disco light controller! The four outputs of the 4017 are high sequencially to the beat of the music. Works SWEET! Adjusting the monostable trigger time really makes the lights go to the music!

    [attachmentid=494]

    I do have a query tho, if anyone can help. Originally I had some different coloured high-brightness LED's from the 4017 with different resistors on them to make them seem the same brightness as each other and I had no diodes in the circuit. I notices that sometimes the monostable would trigger twice without two sound signals, by itself. I then changed the LEDs to the same colour ,same resistance etc and added diodes between the stages and this false triggering stopped ... why is this ? heheh any help would be appreciated. It works fine now though! :D

    Thanks again, David :D
     
  13. Aurbo

    New Member

    May 6, 2005
    9
    0
    Greetings,

    I am looking for something similar in the way of an LED flashing to the input of an audio channel.

    I was thinking of using the Aux out on my radio to drive the audio or just use a y jack to split between the speaker and LED.

    I'm not trying to build a big circuit, I was originally thinking of an audio in jack, through a rectifier through a pot to a single resitor loaded LED.

    Any clues? amy I off the mark? has anyone already created this circuit that I might try for myself.


    Cheers
    Aurbo
     
  14. Sephiroth

    New Member

    May 27, 2005
    1
    0
    Hi i am wanting to do something similar to many of the people here.

    I was thinking of purchasing a sound activated kit from dick smiths which has everything i need for the circuit. Now here is where it starts getting tricky... i own an x-raider mouse pad (one of those USB powered ones with glowing leds). Now i was thinking of adding in a USB plug on either side of the circuit and having the circuit between the red and black pins of the USB, causing the mouse pad to 'dance to the music'. Any ideas on whether this would work or what i could do to make it work better?
     
  15. Aurbo

    New Member

    May 6, 2005
    9
    0

    Greetings David,

    With this circuit, is it possible to replace the Electret Mic with an 8ohm audio input. I think this may work for my project but I want to make sure that a Bright LED and a direct audio input will work without feeding power back into the input lines.

    Cheers
    Aurbo
     
  16. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    Using a 'speaker as a mic? I think it will. Leave out the 10k resistor of course, and try it.

    Or using the output from an amplifier which feeds an 8 ohm 'speaker?

    I don't know what you mean, sorry.
     
  17. Aurbo

    New Member

    May 6, 2005
    9
    0
    Thanks for the reply Dave,

    I seem to have messed up my forum subject and replies,

    My referrence to replace the Electret Mic with an Audio input jack to feed the audio dirctly into the circuit belongs in another thread.

    Sorry about that.


    Cheers
    Steve
    (Aurbo)
     
  18. mmurph

    New Member

    Apr 30, 2006
    1
    0
    I've been looking for a circuit like this for a while. I'd like to use it to control a larger group of LEDs on each part of the controller. Say 20 or so LEDS on each controller. What would be the best way to do this? A relay? I'm not entirely sure what would need to be changed to make this work. Any help (or diagrams) you could provide would be great.
     
  19. Gorgon

    Senior Member

    Aug 14, 2005
    113
    0
    Hi Happs,
    I don't know the type of power supply you use, but you should put in some bypass capacitors to reduce noise on the power lines. 100 uF and a couple of 0.1uF capacitors should do the trick. The diode on the 4017 clock input is not good, it leaves the input floating when the 555 output is low. This may give you extra pulses for the 4017 if you have some noise in your circuit.

    TOK ;)
     
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