PC PSU monitor

Discussion in 'The Projects Forum' started by dawg, Mar 10, 2013.

  1. dawg

    Thread Starter Member

    Nov 15, 2009
    Hey guys gals

    I built a PC PSU monitor

    It has LEDS and a piezo buzzer to indicate low or high volts on the 12v 5v 3v3 power rails on the PSU for PC

    The problem is that it beeps when shutting down

    The residual voltage (at the PSU) at shutdown causes the Piezo to sound off as it is going through a low voltage alarm cos there is some voltage decaying

    Please see fotos of schematic

    I have tried the diodes

    I have tried reducing the cap 100uF tried 10uF no joy

    I will also try using a cap at the Base of Q1 to ground

    There is the option to use relays to cut the voltage off sharp so there would be no residual voltage

    But that is way too complex, I will use 6 PSU monitors and that means 13 relays, a power up circuit and power down circuit

    Way too complex a setup

    Maybe a NPN tranny to sharply cut the supply voltage to the units, but I dont know the math to figure that out

    But for now any suggestion please

    How it works
    LED1 & LED5 are at the top & bottom of the monitoring range
    If they light up they draw current and subsequently Q1 turns ON
    Q1 conducts current and the Piezo sounds off