How to Monitor Current Flow

Discussion in 'General Electronics Chat' started by bsfrye, Mar 1, 2009.

  1. bsfrye

    Thread Starter Member

    Feb 20, 2009
    I want to monitor the amount of current being drawn by a DC motor. What is the easiest way to do this? I have a Microcontroller with analog input... Any ideas?
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    It's easier with some idea if the magnitude of the current.

    In general, a small value resistor in series with the motor will develop a voltage proportional to the current. After suitable amplification, you can read it with a meter or input it to a uC.
  3. masa6614

    Active Member

    Nov 9, 2008
  4. bsfrye

    Thread Starter Member

    Feb 20, 2009
    That chip (ACS712) looks promising. But would be nice if I could just use a resistor as beenthere was saying - Under normal operation my circuit will draw up to about 2 amps. However, my dc motor will stall and draw up to 5 -7. All operating on 6 volts... So how do I hookup a resistor to this and what value should I choose? My microcontroller has a 0 - 5vdc ADC on it.
  5. mik3

    Senior Member

    Feb 4, 2008
    Be aware that high voltage spikes may be developed across the current sense resistor and destroy your circuitry.
  6. russ_hensel

    Distinguished Member

    Jan 11, 2009
    Just a few more words. You could use a special IC but a low side sense resistor of about .1 ohms should convert the current to a measurable voltage. An op amp amplifier ( with cap filer and or diode snubbers ) can be used to boost/shift voltage to one sutiable for the ADC in the PIC. Use a 5 v single supply rail to rail op amp, and you will have a fairly easy time.