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I've wired up a simple circuit using:

  • 9V Battery
  • Blue LED
  • 220 Ohm Resistor

    1. I was expecting a much higher value of mA? Is it true it's only 0.8mA?
    2. Shouldn't the LED light up, since we're closing the circuit with our multimeter?

Thank you!

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  • \$\begingroup\$ Does the LED light when you connect the black jumper directly between the negative end of the battery and the LED? \$\endgroup\$ – Elliot Alderson Aug 9 '18 at 16:11
  • \$\begingroup\$ Are we supposed to understand how you do it from the photo? Draw a schematic of what you are doing and clearly write the values you are getting. \$\endgroup\$ – Eugene Sh. Aug 9 '18 at 16:11
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    \$\begingroup\$ Make sure your LED is the right polarity. Easy way to check is by sticking the end you're sensing the current through to ground. If it turns on, you're good to go. If you have your LED reversed, it won't allow any current to flow. Any reading on the meter is simply an artifact thats being measured by your meter. Also measure the voltage of your battery. Make sure you're getting a nice 9V. \$\endgroup\$ – jaredwolff Aug 9 '18 at 16:17
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    \$\begingroup\$ The low-current fuse inside the multimeter is very vulnerable to blowing, but the 10A fuse is less likely to be blown. Go to 10A range, and move the red banana to the "10Amax" jack. If the LED lights, then the low-current fuse is likely blown. \$\endgroup\$ – glen_geek Aug 9 '18 at 16:52
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    \$\begingroup\$ Tobias, the internal low-current fuse is certainly something to check. Could also be blown shunt resistors - look for over-heated resistors. These will likely be printed-circuit-board-mounted. \$\endgroup\$ – glen_geek Aug 9 '18 at 17:27
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The first thing to do is verify that your equipment works, in a lot of cases measurements that don't make sense can be from measurement error.

First test only the resistor from 9V to ground, you should measure 40mA.

If not then check the fuse and also check the batteries in a meter, low batteries can give false readings.

I also see that the LED is not lit, so this could indicate that it may be damaged. It may also be that the LED is backwards which would be a problem. Check the LED with the diode mode on the meter, it should be around 3.5V for the forward voltage. With the LED and resistor you should get somewhere between 20mA and 30mA. And the LED should be lit.

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