My multimeter has 4 probe sockets. The black probe is the ground (or common-COM) and the red probe is the positive.

If you are measuring voltage or resistance or frequency you plug the black probe into the COM socket (white arrow) and the red probe into the far right socket (red arrow) .

OK so now you know your way around a multimeter lets look at some practical uses.


There are 3 main reasons to use a multimeter;

1.Measuring Voltage

2.Measuring Resistance

3.Measuring current


Voltage requirements vary from circuit to circuit and LED to LED. If you are powering some LEDs you can use anything from 3-12 V if you attach resistors to the LEDs.If you are powering a microcontroller like an arduino you need 5V. You may find that you can find a battery or power supply that provides the voltage or you may need to use a voltage regulator to change the input voltage to match the voltage.The multimeter can check to make sure the voltage you are supplying is what you need.if apply too much voltage to you may damage the circuit or LEDs.


Measuring resistance is really useful if you are using a bunch of resistors in a project.Mark showed you how to read the bands on a resistor to determine the resistance.You can also use a multimeter to check the value of the resistor.I always do this before soldering a resistor onto an LED or circuit because it is a pain de solder and remove a resistor is you mess up.


Measuring current is extremely useful to determine what kind of power supply you need. If you have a circuit that draws 800ma of current and you power it with a battery rated at 800maH the circuit will drain the batter in less than 1 hour. if you buy a DC power supply rated at 1 amp and your circuit needs 2 amps of current the circuit wont work.SO if you can measure thr current draw of your circuit you can pick the best power source.A good rule of thumb is to use a power supply that is rated for at least double the current draw of your circuit because pwoer supplies are rated for maximum current draw and if you are close to that with your circuit the power supply may not be able to consistently provide enough current and weird things may happen to your circuit.
So say your circuit draws 500ma of current I would go for a 1 amp power supply.

Measuring resistance


I have a resistor on my bench .I think it is 470 ohm, but I am too lazy to go online and check the color band coding.So I hook up the probes in the same way as measuring voltage and then switch the selector to resistance.I then connect one probe to one end of the resistor and the second probe to the other end (doesnt matter which way round) and I get 470 ohms. I always check my resistors especially if I am soldering them onto a circuit board because desoldering is a pain.

To use the multimeter it has to be connected in series to the circuit.Here is the modified circuit with the multimeter incorporated.

The positive wire from the power supply is attached to the black probe plugged into the COM socket.The red probe is now plugged into the A socket (far left). When you are not sure how much current will be drawn it is safer to use the higher rated plug because remember the uAmA socket has a 400ma limit. The red probe is then connected to the positive input to the lcd screen.Current passes from the power supply through the multimeter and into the screen. The ground from the pwoer supply still goes to the ground of the screen.

So the power supply is saying 103ma and the multimeter is saying 101ma.Pretty close.

Now I know the screen draws about 100ma of current.So if I want to put it in a hand held prop like a Star Trek Tricorder or Space 1999 communicator I need a battery that can provide 12v with at least 200ma current (remember double the current draw).If I use a boost power converter and a lipoly battery rated at 800mah I could power the screen for several hours.

Great addition to the topic Carl.... Appreciate the effort you've gone to in putting this together and I know it'll be very helpful to members, especially me.... .. Thanks for sharing....

Regards

Alan