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Measuring microamps & milliamps at 3 MHz bandwidth

Posted on Monday, July 29th, 2013 in how-to, measurement by DP

current1

Paul over at Dorkbotpdx writes:

Recently I needed to actually “see” a current waveform in the 100 uA to 5 mA range with at least a couple MHz bandwidth.  This extremely expensive probe would have been perfect, but instead I built something similar for about $30 using the amazing Analog Devices AD8428 amplifier.

This entry was posted on Monday, July 29th, 2013 at 11:00 am and is filed under how-to, measurement. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

4 Responses to “Measuring microamps & milliamps at 3 MHz bandwidth”

  1. blorp says:

    New teensy?

    • The board in the photo is one of several early Teensy 3.0 prototypes. This particular work aims to improve Teensy3’s power usage for battery powered projects. It will soon be published as a software update that improves all existing Teensy 3.0 boards.

      A Teensy++ 3.0 is in development, but technical details of the new chip are still under NDA at this time. :-(

  2. Rubi says:

    Nice!

    I will try this with my Msp430 controllers.
    Always great to measure what is going on there or to see if the low power optimization really worked.

    Please excuse my ignorance, but what microcontroller current consumption are you measuring ?
    I love the violet pcb silk screen.

    Cheers
    Rubi

  3. tom maier says:

    Looks good.

    Here are a few tips on trying to do this:
    – For the current sense resistors (the two 1 Ohms), use either wire wound or metal film composition resistors. Doped metal has the lowest possible noise injection. When you get your tiny millivolt signal you need to start out with the best signal fidelity you can.
    – When trying to go for the high speed measurement, watch out for accidently adding capacitance or inductance to the signal. The breadboard sockets have a fairly high capacitance and so can long leads and DIP sockets. This capacitance can cause injection of unwanted noise and slew distortion and attentuation of the real signal. The sense amplifier should be right on the sense resistors as much as possible.

    High speed transients on the power lines can cause mysterous reboots, jumping over sections of code, and corruption of internal registers. Then you have to power down and clean the junk out.

    That current sniffer can be used for other projects you make.

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