# 11.11: Multimeter

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The multimeter is an essential tool for debugging electric circuits.

## Measuring Voltage

The voltmeter is placed in parallel with the circuit component you wish to measure the voltage drop

Plug the ground probe into the common port and the hot probe  into the voltage port

SparkFun YouTube Video at 2:40 minutes showing how to use multimeter to test for voltage.

## Measuring Resistance

To measure resistance you disconnect the device you are measuring from everything else (make sure to disconnect the power), and then connect the probes across the device.  The multimeter will then send a small current through the circuit and measure the resistance. Note the different ranges have different SI prefixes.

• Reading of 1 indicates the resistance is beyond the range of current setting and you need to increase the range.
• Reading 0f 0.01 indicates the resistance is too small and you need to decrease the range.
• Note, if you are measuring across a polar device like a diode or LED you must send the current in the correct direction (switch the direction of the probes).

SparkFun YouTube Video at 4:59 minutes showing how to use multimeter to test for resistance

## Measuring Current

To measure current you need to set the multimeter in series with the circuit you wish to measure.  Most multimeters have a seperate port for measuring current. Note, you may need an oscilloscope to see fluctuating current due to capacitors, inductors and other electrical components.

SparkFun YouTube Video at 6.32 minutes showing how to use multimeter to test for current

## Applications of Multimeters

### Testing a Battery

0:59 min YouTube by AdaFruit Industries: Test Batteries with a Multimeter - Collin's Lab Notes