How to use a digital multimeter for measuring electronics circuits at home or in the car.

How to use a digital multimeter

Volt meter function

To measure DC voltage, set the multimeter dial to Continuous line V symbol and choose with the dial the maximum value measured and precision.

For example, to measure continuous current 12 Volt, set the voltmeter dial to 20V DC.

Insert the back of the black probe into Com / black port on the multimeter and the red probe into the red multimeter terminal marked with V and continuous line for DC.

How to measure voltage

You touch the red probe to the positive terminal and black probe to the negative terminal.

What voltage to measure

You can measure the voltage of your car battery before crank, during crank voltage drop and while the alternator is running.

Measure rechargeable batteries with the 2V  option or the battery tester mode set to in 1.5V.

Resistance ohm meter function

To measure resistance, the red probe must be moved to the resistance measuring port.

The resistance meter function tests the value of the resistance between 2 points in Ohms.

How to measure resistance

To measure resistance in ohms, you place the probes at the 2 points you want to measure how much resistance is between them.

What to measure resistance on

You can check the resistance in Ohms of a resistor component, a diode, measuring a cable resistance at both ends.
You can also use the continuity tester function that beeps when the probles touch eachother and also beeps if 2 points in a circuit or cable are connected to eachother.

DC Current measuring function

To measure DC current, the red probe must be moved to the current measuring port.

The multimeter has fuses that can be blown if you put too much current thru the multimeter by mistake. Fuses can be replaced easily.

How to measure current

Set to measure DC current at a milliamps value that matches your needs. If you need to measure amperes, you have to use the 10A function.
The probles go in series in the circuit. When you comnect the probes, the circuit is closed otherwise the circuit is open and no current flows until you connect both probes in the circuit.

What to measure current on

You can troubleshoot electronics boards power usage as finding the ma / milliamps or amps value and the voltage you can use Ohms law to calculate the power used in Wats.

Ohm’s Law Formulas

Voltage, resistance, power and current are linked together and by knowing 2 you can find the third value using the simple Ohm’s law formulas.

How to find Voltage from Resistence Current or Power

V or E is voltage or energy it’s usually called E, I guess I like V more so I call it V measured in Volts. Note sqrt reffers to the Square Root function.

V = sqrt(P x R)
V = P / I
V = I x R

How to find Power from Resistence Current or Voltage

P is for power measured in watts.

P = V x I
P = I^2 x R
P = V^2 / R

How to find Current from Resistence, Power or Voltage

I is for cureent measured in Amps or Amperes, don’t ask me why it’s symbol is I.

I = V / R
I = P / V
I = sqrt( P / R)

How to find Resistence from Current, Power or Voltage

R is for reaistance and it is measured in ohms Ω symbol.

R = V / I
R = V^2 / P
R = P / I^2

Diode tester function

You can test diodes with the multimeter diode test function usually you find this at the 2k ohms on the multimeter dial.

How to measure a Diode or LED

Place the probes at both ends of a diode or LED module and measure the resistance.

The diode should allow current flow in one way but block the flow of cureent in the opposite direction.

Also in this mode if you test a LED module, the LED will start working dimly so you know the led tested works.

AC high voltage warning

It’s best not to use the AC high voltage test modes as this can be dangerous. That is made to check rhe voltage of your power sockets on the wall. If you have power supply problems, get an UPS or an extension with built in over voltage protection.


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