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breadboard component; press to break/make circuit and measure current

Discussion in 'Electronic Design' started by oldyork90, May 7, 2013.

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  1. oldyork90

    oldyork90 Guest

    I have a breadboard circuit that requires multiple and frequent
    current measurements. Is there a breadboard component that can break
    and make current measurement connections using a probe?

    The action would be, the circuit is broken as the current meter probe
    presses down on an isolated conductive surface (part of this current
    "tap" switch). After the circuit is broken, further travel connects
    this isolated conductive surface to the input circuit. The circuit is
    now complete again, this time with the current meter in series.

    The circuit would suffer a momentary loss of input, but that is of no
    concern. I could build this, but was hoping there was a nice little
    proto compo I could use.

    Thank you.
  2. I assume you know about clamp-on current meters / probes?
  3. Neon John

    Neon John Guest

    Yes. It's called a diode. Place a diode between your test points so
    that it is forward biased. It will drop about 0.7 volts under normal
    conditions. 0.3 volts or so for a Schottkey diode.

    When you attach your ammeter probes to the test point, the meter's
    current shunt, which drops far less than 0.7 volts, now conducts all
    the current and the diode turns off. Just make sure that your test
    leads are heavy enough not to drop significant voltage.

    Using this method there is no interruption of the circuit, not even a
    glitch as the meter is connected and disconnected.

    John DeArmond
    Tellico Plains, Occupied TN
    See website for email address
  4. whit3rd

    whit3rd Guest

    Sure, just put in a momentary contact NC pushbutton. It has
    to be normally closed (NC) so the current meter can be unplugged.

    To make a current reading, plug in the current meter (across the
    switch) and push the button, then read the meter.

    The voltage burden on the meter may allow other switch types (like a pass diode),
    or you might be able to do Hall effect measurements of DC current in a wire loop, but
    those get into accuracy and functional and cost tradeoffs.
  5. oldyork90

    oldyork90 Guest

    Went with the momentary. Thank you. Good suggestion.
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