mulitimeter help

[LaCozTe-2028]

ok so could anybody tell me how to find a + and a negative source with it and how blizzerd and other ppl finds the ground thing and stuff

**edit** so now that kick has given me a proper class on all of the acid mods rules dont want to break the so . wow gr8npwrfl you are a true jedi now time to go poke my mobo for my new mod shake reactive lights i ripped the pcb of a toy and moded it a bit so i could have 2 modes direct current or to turn on for a few seconds flashing but i dont know what to do that or a pulse muv chip please give me your opinion.

[psp339]

yea i would like to know how to use the multimeter too. i got one but no idea how to use mine.

[gr8npwrfl]

These articles are in part from http://www.ladyada.net/library/metertut/index.html

Part 1

Introduction

The most important debugging tool in any E.E.'s toolbox is a trusty multimeter.
A multimeter can measure continuity, resistance, voltage and sometimes even current,
capacitance, temperature, etc. It's a swiss army knife for geeks!

What you will learn!

You should go through all of these sections in order, as they build on each other.

   1. Continuity measurements
      How to tell if two points are electrically connected

   2. Resistance measurements
      How to measure resistance - resistors, potentiometers and sensors

   3. Voltage measurements
      How to measure voltage - battery testing, wall-wart adaptor testing, and
      the terror of mixed AC/DC measurements.

What is continuity?

You might be asking, "What is continuity?" But don't worry, it's quite simple! Continuity means,
are two things electrically connected. So if two electronic parts are connected with a wire,
they are continuous. If they are connected with cotton string, they are not: while they are
connected, the cotton string is not conductive.

You can always use a resistance-tester (ohmmeter) to figure out if something is connected
because the resistance of wires is very small, less than 100 ohms, usually. However,
continuity testers usually have a piezo buzzer which beeps. This makes them very useful
when you want to poke at a circuit and need to focus on where the probes are instead of
staring at the meter display.

For some basic circuits you can just look to see where the wires go to determine continuity
but it's always wise to use a multimeter. Sometimes wires break or you're tired and can't
easily follow all the PCB traces. I use continuity check all the time!

What is it good for?

Continuity is one of the most important tests. Here are some things it is good for

    * Determine if your soldering is good. If your solder joint it is a cold solder connection
      it will appear connected but in actually it is not! This can be really frustrating if you
      are not experienced in visually detecting cold solder joints
     
    * Determine if a wire is broken in the middle. Power cords and headphone cables are notorious
      for breaking inside the shielding, it appears as if the cable is fine but inside the wires
      have been bent so much they eventually broke.
     
    * Making sure something isn't connected. Sometimes a solder joint will short two connections.
      Or maybe your PCB has mistakes on it and some traces were shorted by accident.
     
    * Reverse-engineering or verifying a design back to a schematic

Remember!

You can only test continuity when the device you're testing is NOT powered. Continuity works by
poking a little voltage into the circuit and seeing how much current flows, its perfectly safe
for your device but if its powered there is already voltage in the circuit, and you will get
incorrect readings

Always test to make sure your meter is working before starting the test by brushing the two
tips together, and verifying you hear the beep. Maybe the battery is low or its not in the
right mode.

Continuity is non-directional, you can switch probes and it will be the same.

If you are testing two points in a circuit and there is a (big) capacitor between those points
you may hear a quick beep and then quiet. That's because the voltage the meter is applying to
the circuit is charging up the capacitor and during that time the meter 'thinks' its continuous
(essentially)

Small resistors (under 100 ohms or so) and also all inductors will seem like short circuits to a
multimeter because they are very much like wires.

Likewise, continuity doesn't mean "short" it just means very very low resistance. For example,
if you have a circuit that draws an Amp from a 5V supply, it will appear to be a 5O resistor.
If you measure that with your meter it will think its a short circuit, but really its just a
high-drain circuit.

Get into the mode

First step is to get your multimeter into the correct mode. Look for the icon that looks sort
of like a 'sound wave'

Here are three examples. Note that sometimes the mode is "dual" (or possibly more) usage,





Turn the multimeter knob so that it points to this symbol

Touch and go

For a majority of multimeters, you're ready to go, just touch the tips of the probes together
so that they make a beeping sound!

Here are some examples covering a couple of different multimeters

Example 1

This meter is very simple. When the probes are not touching, the display shows "1"



When you touch the tips together, the display changes to a three digit mode (it's displaying
resistance, which we will cover later) It also emits a beep



Example 2

This meter is dual-mode but still very easy to use. Turn the dial to the symbol.
When the probes are not touching the display shows "OL" which stands for Open Loop.
(Open loop is another way of saying there is no continuity)



When you touch the probes, the soundwave icon shows up in the display (upper right)
and it also shows a number. The number is not the resistance, actually...its the voltage
(look for the V in the right hand side for Volts). This is because this mode is also a
Diode Test (which will be discussed later)



Example 3

This meter is triple-mode and requires an extra step to get to the continuity
function. Click on the image to get a closer view of the triple-mode. After you dial
to this mode you must press the Mode button, the wave icon will then appear in the
display.



You can see the wave icon in the top right as expected. This meter also displays
OL (I've noticed that nicer meters do this)



Unlike the other meter, this one displays Ohms (see the symbol on the right of
the display). The resistance is low (4.7Ohms) but not 0 (the ideal value) because
the probes and wires act as resistors. Usually with these sorts of meters they will
beep whenever resistance is under 100 ohms or so.


 
Probing a PCB

Here is an example of testing a PCB for continuity.The first test shows that
the two points are not connected.



The second test shows that these two points are connected



What is resistance?

Resistance is just what it sounds like, its the characteristic that makes a component
fight current flow. The bigger the resistance value (in ohms O) the more it fights.
Most resistors you'll see range between 1 ohm and 1 megaohm (1.0 MO) they often have
5% tolerance but you can buy 1% or even 0.1% accuracy resistors.

In general, resistance testing is best for measuring resistors, but you may find yourself
measuring the resistance of other things, such as sensors and speakers.

Resistor coding

Resistors are color coded, at first it seems like a bad way to print the values but
with a little time it becomes faster because you dont have to read any numbers and the
stripes are visible no matter how it is rotated. You can use this calculator to play
around with resistor color codes

Remember!

You can only test resistance when the device you're testing is not powered. Resistance
testing works by poking a little voltage into the circuit and seeing how much current
flows, its perfectly safe for any component but if its powered there is already voltage
in the circuit, and you will get incorrect readings

You can only test a resistor before it has been soldered/inserted into a circuit. If you
measure it in the circuit you will also be measuring everything connected to it. In some
instances this is OK but I would say that in the vast majority it is not. If you try, you
will get incorrect readings and that's worse than no reading at all.

You can make sure your meter is working well by having a 'reference resistor' to test against.
A 1% 1KO or 10KO resistor is perfect! Low batteries can make your multimeter wonky.

Resistance is non-directional, you can switch probes and the reading will be the same.

If you have a ranging meter (as most inexpensive ones are), you'll need to keep track of what
range you are in. Otherwise, you will get strange readings, like OL or similar, or you may
think you're in KO when really you're in MO. This is a big problem for beginners so be careful!

Get into the mode

Look for an ohm (O) symbol, if its a ranging meter there will be a bunch of subdivided modes.
If its auto-ranging there will be only one.

This meter has the O symbol and then 7 submodes, ranging from 200O to 2000MO (wow!)



This meter has the O symbol and then 5 submodes, ranging from 200O to 2MO



This meter has a multi-mode (you need to press a seperate MODE button to change between
capacitor sense, diode test, resistor test and continuity!) It does not, however, have any
numbered submodes, as it is auto-ranging



Ranging vs. Auto-ranging

As long as it works, it doesn't matter which type you have. But auto-ranging meters are a
little slower.

Which takes about 4 seconds to settle on a final value, and a 10KO resistor with a ranging meter:

With an auto-ranging meter, its easy, just put the two probes across the resistor and read the
number. For example, this 1KO 5% resistor is actually 0.988 Kohm.



And this 10KO is really 9.80KO. Note that the numbers look similar but the decimal point has moved.



This ranged meter requires that you dial in the range. We'll guess that this resistor is under 2KO
then measure it. We get 0.992 which means its 0.992 KO (or, a 1KO resistor)



Now testing a different resistor, we will again guess its under 2KO. However, this time we get a
strange response, a 1. which means out of range. Some meters will display an OL which you may
remember from the continuity secion as meaning "open loop" here it means "the measurement is
higher than the range"



We try again, changing the range to 20KO



Aha! It is a 9.82 KO resistor (10KO)

Its a little clumsier than auto-ranging but if you are pretty sure you know about how big the
resistance you are expecting is, its very speedy.

Example 2. Testing a potentiometer

You can test the max-value of a potentiometer by measuring across the two 'ends' as shown
here with a rotational 10KO pot. To find the 'range' look at the dial.



You can also use a multimeter to tell whether the potentiometer is a linear or logarithmic
(audio) pot. When the pot is centered, if the resistance between the wiper and one end is
half of the total value, its linear. (I used clips instead of probles to make it easier to
take these photos)

This is a 10KO linear potentiometer



The minimum resistance of the pot, 0O (a short) as expected



Potentiometer centered, about 5KO



Maximum value is 9.5KO (it should be around 10KO)

Here are photos of a 50KO audio potentiometer



Minimum is 0O as expected



Middle is 8KO



Maximum is 54.2KO, close to the ideal 50KO

If, when centered, the resistance is more like 85% or 15% of the total resistance, then
its a log pot. This is a 50KO analog potentiometer. When centered, the resistance is about 8KO.

Potentiometers are resistors that change value when they are moved. A Light Dependent Resistor
(LDR) is a resistor that changes value with the amount of light it receives. This one has a
range of about 20K max.

First, set the range, in this case 20KO seems pretty good. In bright light, it measures about
610 O



Slightly shaded it's 5.84KO (remember this is still a well-lit photo)



See Part 2

[Bhawan]

ok set the multimeter to voltage mode (if on a psp or something its the DC volt one) and then use the tester things and if it just shows a number then the point on the red tester is + and if it says [-] beside the number then the point on the red one is [-]. i hope that helps

[gr8npwrfl]

Part 2

What is voltage?

So what is voltage anyhow? Well, its a pretty abstract term but a lot of people like to use the
term "potential energy" which is that thing you heard about in high school physics and then forgot
immediately.

Some people like to draw an analogy to water to describe voltage. A water pump is like a voltage
supply (also known as a battery).

The pump pushes water through a hydraulic system, and the voltage supply pushes electrons through
an electronic system.

The higher the rated pressure of the pump, the more 'work' the water can do.
Likewise, the higher the voltage the more 'work' (Watts) the electrons can do.

Voltage is used to provide power (via a battery or wall plug) and its also used as a way of
transmitting data. For example, music is recorded from a microphone as an analog voltage signal,
if that voltage waveform is applied to a speaker the voltage performs the work of making air move
and produces sound.

Voltage is also used to in digital circuits to talk back and forth in binary, usually 5V or 3.3V
is a "1" and 0V is a "0", by alternating the 1's and 0's millions of times a second, data can be
moved around rather quickly.

AC/DC

Not just an 80's hair metal band! Voltage comes in two flavors (yum): Alternating Current (AC)
and Direct Current (DC). Here is a quick tour of the differences.

Direct current voltage is what comes out of batteries. The battery is at 9V, and it pretty much
keeps that voltage constant, until it dies. The chemical reactions inside the battery creates DC
voltage.

Electronic circuits really like DC voltage.

Alternating current voltage is what comes out of the wall. The generator at the US power plant
creates a voltage that oscillates, going from -60V to 0 to +60V to 0 again, 60 times a second.
At the European power plant its -120V to +120V at 50 times a second.

AC voltage is great for power plants because its easy to transform AC voltages (using a transformer)
up to 50KV for long distance travel and then down to 240V or 120V to safely power your home. Those
big honking grey things that you see next to buildings that hum are the huge transformers.

Motors (like your washing machine and refrigerator compressor pump) like running off of AC voltage.

You can turn AC voltage into DC voltage very easily by using a very small transformer to bring the
120V down to a reasonable level like say 16VAC and rectifier. This is basically what's inside a wall
wart plug or your laptop power supply.

Its much harder to turn DC into AC, you will need an inverter which are more expensive than
transformers/rectifiers.

Batteries only supply DC voltage and wall plugs only supply AC voltage. However, it is totally
possible to have both AC and DC voltage at a certain point:

If an AC voltage is oscillating between -60V and +60V it has 120V AC and 0V DC because the
average voltage of -60V and +60V is 0V.

If an AC voltage is oscilating between 0V and 120V then it has 120V AC and 60V DC because the
average voltage of 0V and 120V is 60V.



In the above oscilloscope image, the dashed horizontal line in the center is ground (0V) and each
dashed division is 5V. The scope is displaying a signal that has both AC and DC components. There
is an alternating voltage (a square wave) that is about 4V high at about 100Hz and a DC
(mean average) voltage that is around 7V. Use the dashed divisions to verify for yourself that
this is so.

What is voltage testing good for?

Voltage testing is very common, you'll use it a lot

    * Test if your power supply is working, are you getting 5V out of that 7805 regulator?
    * Verify that your circuit is getting enough power: when all of the blinky lights are on,
      is the power supply drooping too low?
    * Verify signals to and from chips to make sure they are what you expect once the circuit
      is up and running
    * Testing batteries, solar cells, wall plugs, and power outlets (carefully!)
    * With a current sense resistor you can perform current testing on a project without
      possibly damaging your meter.

Remember!

You can only test voltage when the circuit is powered If there is no voltage coming in
(power supply) then there will be no voltage in the circuit to test! It must be plugged
in (even if it doesn't seem to be working)

Voltage is always measured between two points There is no way to measure voltage with only
one probe, it is like trying to check continuity with only one probe. You must have two
probes in the circuit. If you are told to test at a point or read the voltage at this or
that location what it really means is that you should put the negative (reference, ground,
black) probe at ground (which you must determine by a schematic or somewhere else in the
instructions) and the positive (red) probe at the point you would like to measure.

If you're getting odd readings, use a reference voltage (even a 9V battery is a reasonable
one) to check your voltage readings. Old meter batteries and wonky meters are the bane of
your existence but they will eventually strike! Good places to take reference voltages are
regulated wall plugs such as those for cell phones. Two meters might also be good

Voltage is directional If you measure a battery with the red/positive probe on the black/
negative contact and the black probe on the positive contact you will read a negative voltage.
If you are reading a negative voltage in your ciruit and you're nearly positive (ha!) that this
cannot be, then make sure you are putting the black probe on the reference voltage
(usually ground)

DC voltage and AC voltage are very different Make sure you are testing the right kind of
voltage. This may require pressing a mode button or changing the dial.

Unless otherwise indicated, assume DC voltages

Get into the right mode

There are often two seperate modes for AC and DC voltage. Both will have a V but one will
have two lines, one dashed and one solid (DC) and one with have a wave next to it (AC).



This meter has the double line for DC voltage, and 5 ranges, from 200mV to 600V. The lightning
bolt symbol is a gentle reminder that this voltage is extremely dangerous.



There is also the V-wave symbol for AC, and two ranges since most AC voltages that are measured
are power voltages and are pretty big. (For small AC waveforms, a scope is best since you will
be able to see the waveform itself)



This autoranging meter makes it pretty clear which mode you want to be in



This ranged meter has 5 ranges, the top range is 750 VAC or 1000 VDC, to switch between DC and
AC you need to press the DC/AC button on the upper right.

When the probes are not connected to anything, they should display 0V. They might flicker a
bit if they pick up ambient voltage (your home is a big radiator of 60Hz voltage which can
couple into your meter probes).



Example 1: Testing batteries

Testing batteries is a super useful skill and is one of the best ways to practice with your
multimeter

The first battery we'll test is a new 1.5V alkaline. This one is a AAA but a AA, C or D cell
will be the same voltage. Set the range to 2V DC .



We read 1.588V, which you may think is a mistake, after all its a 1.5V battery so shouldn't it
be 1.5V? Not quite, the 1.5V written on the side is just a nominal voltage, or the "average"
you may expect from the battery.In reality, an alkaline battery starts out higher, and then
slowly drifts down to 1.3V and then finally to 1.0V and even lower. Check out this graph from



Using this graph you can easy tell how fresh your battery is and how long you can expect it to last.

Next, we measure a 9V alkaline battery. If we still have the range set to 2VDC we will get a
mysterious "1. " display, indicating is it over-range.



Fix the range so that it's 20V, and try again.



For this new battery we get 9.6V. Remember that battery voltage is nominal, which means that
the "9V" is just the average voltage of the battery. In reality, it starts out as high as 9.5V
and then drops down to 9 and then slowly drifts to 7V. You can check out the discharge curve in
the Duracell 9V datasheet

If we want to check a rechargeable AA battery, and it's set to a 20VDC range, we will read 1.3V,
which is about what a fully charged NiMH battery will measure.



If we fix the range so it's 2VDC, we can get an extra digit of precision. This meter probably
isnt more than 0.5% accurate so the precision may not mean much.



Finally, I test a lithium 3V coin cell, its at 2.7V which means it's getting near the end of
it's life.



Example 2: Testing wall wart (adapter) plugs

Testing wall adapters is also very handy, especially when you build your own circuits.

The first kind we will test is a transformer-based adapter.





Note that the label says Transformer, its also blocky and heavy which indicates a transformer
as well. It requires 120VAC input, US power only. The nominal output is 9VDC at 300mA. The
polarity symbol shows that the middle is positive, the outside is negative, thus we place the
ground (black) probe on the outside and the positive (red) probe on the inside.



Yow! 14V? That's not anything like the 9V on the package, is this a broken wall wart? Turns out,
its totally normal. Transformer-based wall adaptors are (almost always) unregulated, which means
that the output is not guaranteed to be a particular value, only that it will be at least what is
printed on the box. For example, with this adapter it means that when drawing 300mA, the voltage
is guaranteed to be higher than 9V.

Since the output is unregulated, the voltage supplied will droop as more current is pulled from
it, which means that open-circuit (connected to nothing) the measured output can be as high as 14V.
Glitchbuster has a long page that describes this.

Next, lets check out a Switch-mode adapter



Notice that it's not square, its much thinner and although you cant feel it, its quite light for
its size: There is no big honking transformer inside!



Note that it says Switching (not Transformer) on the label, and you can input US or European power.
Like the transformer adapter, it is center-positive polarity.



Switch-mode wall adapters are regulated which means that the output doesn't droop from open-circuit
to full load. Its not an ultra-high quality supply, the voltage is 12.2V which is less than 5% error.
Still, its much better than the transformer's 50% error!

Lastly, we'll test a 9VAC adaptor, which outputs AC voltage instead of DC. Basically this means that
there's still a transformer inside, but no rectifier. This is also an unregulated supply



Note that is is similar to the transformer-based DC supply we checked out first



Note again that the label says transformer. It requires 120VAC input, US power only. The nominal
output is 9VAC at 300mA. The output is indicated twice, once at the top "AC/AC" and then again in
the output designator "9V AC"

There is no polarity because AC adaptors are not polarized: AC power oscillates between positive
and negative voltages.

We test the output, but get 0V! That's when we remember that the multimeter has to be in AC
voltage mode.



Switching over to AC, we get a good reading, 10.5VAC. This is an unregulated supply so again we
are going to get a voltage higher than 9V.


 
Example 3: Testing Wall output

This is the 'easiest' test, just shove the two probes into a wall socket. If you're clumsy and
think you'll somehow electrocute yourself, don't do this. Many people freak out about this test,
but ironically it's what the multimeter was designed to do.



About 120V, as expected

Conclusion

So now you have seen the basics on using a meter. All you have to remember is most of the metal parts
on your PSP are grounded and you can take the black lead of your meter to use that for ground and
probe around your PSP for the voltages you are looking for.

PLEASE be careful as you will have the power on your PSP and of you short things out with the meter
you can blow out parts or fuses.