How to Use a Multimeter

Pages

Contributors: Nate

Measuring Resistance

Normal resistors have color codes on them. If you don’t know what they mean, that’s ok! There are plenty of online calculators that are easy to use. However, if you ever find yourself without internet access, a multimeter is very handy at measuring resistance.

Pick out a random resistor and set the multimeter to the 20kΩ setting. Then hold the probes against the resistor legs with the same amount of pressure you when pressing a key on a keyboard.

alt text

The meter will read one of three things, 0.00, 1, or the actual resistor value.

  • If the meter reads 9.90, well then you’ve got a 9.90k Ohm (Ω) resistor (remember you are in the 20kΩ or 20,000 Ohm mode so you need to move the decimal three places to the right or 9,900 Ohms).

  • If the multimeter reads 1 or displays OL, it’s overloaded. You will need to try a higher mode such as 200kΩ mode or 2MΩ (megaohm) mode. There is no harm if this happen, it simply means the range knob needs to be adjusted.

  • If the multimeter reads 0.00 or nearly zero, then you need to lower the mode to 2kΩ or 200Ω.

Remember that many resistors have a 5% tolerance. This means that the color codes may indicate 10,000 Ohms (10kΩ), but because of discrepancies in the manufacturing process a 10kΩ resistor could be as low as 9.5kΩ or as high as 10.5kΩ. Don’t worry, it’ll work just fine as a pull-up or general resistor.

alt text

Let’s say you go into 2kΩ mode and the multimeter reads “0.329” (0.33 of the 1,000 setting is 330), then you probably have a 330Ω resistor commonly used to limit current into LEDs. As a rule of thumb, it’s rare to see a resistor less than 1 Ohm. Remember that measuring resistance is not perfect. Temperature can affect the reading a lot. Also, measuring resistance of a device while it is physically installed in a circuit can be very tricky. The surrounding components on a circuit board can greatly affect the reading.


Want more information about SparkFun's classes? Interested in getting involved with teaching electronics? Just want to talk? Sign up for our newsletter, or contact our education department.

SparkFun is a company built around one core idea – sharing ingenuity. We think everyone should have the hardware and resources to learn and play with cool electronic gadgetry.

Share, give, learn, SparkFun.

Do you regularly instruct classes and workshops in a formal or informal learning environment? SparkFun offers Educator Discounts to people teaching and sharing electronics.

Find out more.