How DMM works? How to o/p to MCU?

Discussion in 'General Electronics Chat' started by Merlysys, Jan 21, 2014.

  1. Merlysys

    Thread Starter New Member

    Nov 17, 2013
  2. MrChips


    Oct 2, 2009
    The chip under the big blob is much more than an ADC.
    It contains a complete MCU that would contain the ADC, switch inputs and LCD driver.

    Most inexpensive DMM will not have a computer interface. If you shop around you will find DMM with RS-232 or USB interfaces (or even GPIB and SCSI if you want to go that route).
  3. cl10Greg

    Active Member

    Jan 28, 2010
    Voltage mode
    The big resistors are used for current limitation A small current is feed to the load and then amplified and analyzed by the MCU that gives you a voltage.

    Current mode
    The resistor is used as a sense resistor. The current flows through the resistor and the MCU analyzes the different from before and after the resistor. The voltage difference and known resistance gives the resistance. This should always be fused for protection.

    You should be able to ID the shunt resistor (very small resistance, milliohms) to find the voltage input pins to the MCU. The output port is obviously the load so you could trace that to see what resistor is for which mode and that would tell you some pinning for the MCU.
  4. takao21203

    AAC Fanatic!

    Apr 28, 2012
    cheap DMM does not neccessarily contain a controller. it is just an LSI chip containing A/D and display drive.