Bass reactive LEDs

Discussion in 'The Projects Forum' started by AkshayVernekar, Jun 16, 2013.

  1. AkshayVernekar

    Thread Starter New Member

    Jun 16, 2013
    1
    0
    Hi all,
    I am currently working on a project that involves filtering the LOW frequency(<200Hz) using a LPF and amplifying the output using a LM741 and passing the output to LEDs. i tested the same circuit with Multisim and it is simulated correctly. but now, when i power up the circuit the LEDs light up without any input voltage . i checked the connections and the connections are correct. Please help
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    In the off-state, the 741 does not turn off completely (it may even be on enough to keep a red LED on).

    You will need to post your circuit so we can give you advice to tweak what you have. Otherwise, there are many ways to start over - you don't want to do that.
     
  3. sq-aristo

    New Member

    Jun 1, 2013
    20
    1
    Just curious for myself would a pull down resistor work or cook the 471?
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,073
    3,856
    A pair of pull-down resistors in series will work best. That way, when the 741 swings within 2 volts of ground, the pair of resistors making the voltage divider can swing much closer to ground. A 100 ohm and 1000 ohm resistor will allow the point in between to reach 0.2 volts (approximately).

    Note that the more modern standard op amps can provide about 30 mA, the old 741 should be kept well below that, If I remember correctly. Use an audio amp lm386 if you need more power. You can also add a transistor to the output of the opAmp to boost current to drive more LEDs
     
    Last edited: Jun 17, 2013
    sq-aristo and mkbutan like this.
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