Need LM3915 help!!!

Discussion in 'The Projects Forum' started by monkeymizfit, Dec 5, 2010.

  1. monkeymizfit

    Thread Starter New Member

    Dec 5, 2010
    I am looking for a very simple mono vu meter with 1 row of at least 20 LEDs. I am using a LM3915 and this simple diagram:

    It works great with a headphone input, but I added a second and I can't get them to work together. It is driving me crazy! Any way I wire it they both work independently. Some tutorials say you can link pin 4 on the first chip to pin 6 on the next, but that doesn't work. Please email me if anyone has a simple solution to this problem or a different route completely.
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    See Page 7 and 8 of the LM3915 Datasheet It shows an example of cascading two ICs together to form one 20dB scale.
  3. SgtWookie


    Jul 17, 2007
    Audioguru posted such a circuit awhile back. If I remember correctly, his was designed to work with line-level input signals.

    There is more to cascading the LM3915 then there is to cascading the LM3914; you have to set the voltage for the RHI and RLOW for the point where the two drivers interconnect, otherwise the response will not be logarithmic.
  4. Audioguru

    New Member

    Dec 20, 2007
    The datasheet for the LM3915 shows that the low level one uses an opamp with a gain of 30dB to feed its input. Then the second one operates at normal input levels.