Over-current interrupt problem

Discussion in 'Programmer's Corner' started by Dritech, Apr 7, 2012.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    Hi all,

    I am using a shunt resistor and a voltage comparator (lm393) as a motor over-current sensor. The circuit that i am using is the one attached.
    The output of the LM393 is connected to a microcontroller interrupt pin. The interrupt is disabled for the first few seconds when the motor starts so that the interrupt wont be active by the starting current.

    The problem is that the interrupt is getting active even when V- is less than V+ , and with the multimeter Vout is showing as 5V (i.e. no over current).

    Does anyone know what can be casing the interrupt to get active, even when Vout is 5V ?
  2. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    Any help please?
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    I suspect if you had an oscilloscope you would see short pulses of current. Motors don't draw a steady DC, they grab current in chunks.

    Try adding an RC low pass between the shunt ans the amp input to filter spikes out.
  4. chrisw1990

    Active Member

    Oct 22, 2011
    id be interested in a more detailed diagram of how you are driving the motor? if possible? be interesting as an alternative route to same outcome might be suggested
    i think ernieM is right.. dont think iv seen a time, on here at least, when he hasnt! :D