Led circuits

Discussion in 'The Projects Forum' started by Interitus, May 6, 2010.

  1. Interitus

    Thread Starter Member

    Nov 8, 2009
    Ok I've made a RB2 drumkit with pads that light up with LEDs when struck. It's all running on 5V power, using the resistors that came with the LEDs, which are 100ohm. There are 5 pads in total, each with its own control board, but sharing the same power supply. Here is the schematic of my circuit:

    I am soon going to be switching to new RGB LEDs, and to 12V power, but I plan on using the same circuit board. As a power source, I would like to use an old computer power supply, as it provides more than enough power, should be pretty clean and stable, and best of all its free. But the PSU I'm testing right now seems to vary a little, and with little load on the PSU, I'm only getting 11.7V on the 12V rail.
    Right now I only have 5 red LEDs in parallel on the 5V rail (with a resistor per LED), so with not much of a load, that may be causing the 12V to be incorrect. Would a better load, such as a power resistor, correct the voltage to be closer to 12V, or even past 12 to something near 12.3V? Another guy I know is also using a PSU for power, and thats what he is getting. What effect would it have on my LEDs?

    The mosfet in my circuit can handle up to 10 LEDs, and I am going to try and have about 7 to 10 LEDs per circuit, Not sure yet as I havent decided how I'm going to light my drum kit yet. If I decide I want more than 10 per circuit board, I would have to add more mosfets, which I would do by adding them in parallel right? Sources to the ground, Gates being fed from the piezo, and a seperate array of LEDs per Drain connection? Would a piezo even be able to drive two or more mosfets?

    ...apologies if the post is disjointed and hard to read, am a bit tired...
  2. Bernard


    Aug 7, 2008
    Using 12V supply, each 1N7000 can drive 10 strings or 3 LEDs in series with 1 100 ohm / string for 30 LEDs per unit provided that the piezo ckt can deliver about 10V pulse. Should be able to connect several 2N7000 to one piezo ckt. If gate drive is low, add non inverting amplifier made from 2 2N7000's and then can drive a room full of FETs.