Low current measurement (mA and uA) of a Bluetooth/Wi-fi modules

Discussion in 'General Electronics Chat' started by mscerri, Mar 21, 2015.

  1. mscerri

    Thread Starter New Member

    Nov 22, 2012
    10
    0
    Please Help!

    Dear All,

    I am new to this forum.

    I am having some issues to measure current in low power devices. I have built a transimpedance amplifier (current to voltage converter) from the knowledge I obtained in some books and the internet. Amplification is necessary as my oscilloscope does not have enough resolution to capure sleep/standby events. I would like to observer what's happening by connecting it to an digital oscilloscope. However I am sure I missing something as I am not obtaining the expected results.

    From the attached image you can see my current setup. I am using a single rail OPA335 opamp for the transimpedance amplifier. The output and ground are connected a multimeter. A +5V is supplied through a 220 ohm resistor and an LED (I also tried it without an LED). The non-inverting pin it connected to the '-' of the LED and the inverting pin to the supply ground.

    The reading on the multimeter is completely off when testing with a 220ohm, 1K and 10K resistors.

    Any help would be greatly appreciated.

    Thank you in advance!
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,447
    3,363
    Details, details, details.

    What is this "low power device"?

    Connect an ammeter in series with the power input to the device. You should be able to measure down to 0.1μA on the lowest current scale.
     
  3. mscerri

    Thread Starter New Member

    Nov 22, 2012
    10
    0
    Hi, first of all thank you for your reply.

    I want to build a generic current measurement circuit that is able to convert current to voltage measurements. For example currently I would like to measure power consumption of the Wi-Fi daughter board TI CC3000. I do not have an ammeter with uA resolution and besides I would like to have a plot on an oscilloscope.

    Thank you!
     
    Last edited: Mar 21, 2015
  4. Papabravo

    Expert

    Feb 24, 2006
    10,148
    1,791
    If you're not getting reasonable results it tells me you don't know how to measure current with a multimerter, or a transimpedance amplifier. The picture is nearly useless as a method of conveying information. A schematic would help.
     
  5. mscerri

    Thread Starter New Member

    Nov 22, 2012
    10
    0
    I resolved the isssue i had with my circuit. Thanks anyway. Didn't know I had to spell out everything for you.
     
  6. mscerri

    Thread Starter New Member

    Nov 22, 2012
    10
    0
    I resolved the isssue i had with my circuit. Thanks anyway. Didn't know I had to spell out everything for you.
     
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