Some Experiments with the help of Multimeter

LED when exposed to light,it generate DC voltage:-

Now switch multimeter to the lowest DC voltage range available, and touch the meter's test probes to the terminals (wire leads) of the light-emitting diode (LED). An LED is designed to produce light when powered by a small amount of electricity, but LEDs also happen to generate DC voltage when exposed to light, somewhat like a solar cell. Point the LED toward a bright source of light with your multimeter connected to it, and note the meter's indication.

Motor Acts As Generator:-

Another source of voltage through energy conversion a generator. The small electric motor specified in the "Parts and Materials" list functions as an electrical generator if its shaft is turned by a mechanical force. Connect voltmeter (multimeter, set to the "volt" function) to the motor's terminals just as connected it to the LED's terminals, and spin the shaft with fingers. The meter should indicate voltage by means of needle deflection (analog) or numerical readout (digital).

If it difficult to maintain both meter test probes in connection with the motor's terminals while simultaneously spinning the shaft with fingers, one may use alligator clip "jumper" wires.

Multimeter  fuse checking:-

One may test the condition of a multimeter's fuse by switching it to the resistance mode and measuring continuity through the test leads (and through the fuse). On a meter where the same test lead jacks are used for both resistance and current measurement, simply leave the test lead plugs where they are and touch the two probes together. On a meter where different jacks are used, this is how one insert the test lead plugs to check the fuse.

Bread board continuity:-

Although multimeter is capable of providing quantitative values of measured resistance, it is also useful for qualitative tests of continuity: whether or not there is a continuous electrical connection from one point to another. For instance, test the continuity of a piece of wire by connecting the meter probes to opposite ends of the wire and checking to see the the needle moves full-scale. What would we say about a piece of wire if the ohmmeter needle didn't move at all when the probes were connected to opposite ends?

Digital multimeters set to the "resistance" mode indicate non-continuity by displaying some non-numerical indication on the display. Some models say "OL" (Open-Loop), while others display dashed lines.

Use meter to determine continuity between the holes on a breadboard: a device used for temporary construction of circuits, where component terminals are inserted into holes on a plastic grid, metal spring clips underneath each hole connecting certain holes to others. Use small pieces of 22-gauge solid copper wire, inserted into the holes of the breadboard, to connect the meter to these spring clips so that one can test for continuity.

How to use a MultiMeter

Usage of Multimeter

Note: Multimeter being used to measure the varies quantities such as Voltage ,Resistance, Current.Apart from this it is also used in continuity test, diode check etc.

Multimeter

Description: 

A multimeter is an electrical instrument capable of measuring voltage, current, & resistance.Digital multimeter have numerical displays, like digital clocks, for indicating the quantities. Analog Multimeter indicate these quantities by means of a moving pointer over a printed scale.

Some digital multimeters are autoranging. An autoranging meter has only a few selector switch (dial) positions. Manual-ranging meters have several different selector positions for each basic quantity: several for voltage, several for current, and several for resistance. Autoranging is usually found on only the more expensive digital meters.

Set multimeter's selector switch to the highest-value "DC volt" position available. Autoranging multimeters may only have a single position for DC voltage, in which case need to set the switch to that one position. Touch the red test probe to the positive (+) side of a battery, and the black test probe to the negative (-) side of the same battery. The meter should now provide with some sort of indication. Reverse the test probe connections to the battery if the meter's indication is negative (on an analog meter, a negative value is indicated by the pointer deflecting left instead of right).

If meter is a manual-range type, and the selector switch has been set to a high-range position, the indication will be small. Move the selector switch to the next lower DC voltage range setting and reconnect to the battery. The indication should be stronger now, as indicated by a greater deflection of the analog meter pointer (needle), or more active digits on the digital meter display. For the best results, move the selector switch to the lowest-range setting that does not "over-range" the meter. An over-ranged analog meter is said to be "pegged," as the needle will be forced all the way to the right-hand side of the scale, past the full-range scale value. An over-ranged digital meter sometimes displays the letters "OL", or a series of dashed lines. This indication is manufacturer-specific.

ILLUSTRATION

Voltage:

Voltage is the measurement of electrical “push” ready to motivate electrons to move through a conductor.It is the specific energy per unit charge,defined as joules per coulomb. It is analogous to pressure in a fluid system: the force that moves fluid through a pipe, and is measured in the unit of the Volt (V).

INSTRUCTION

To measure voltage, follow these steps:

1. Plug black and red probes into the appropriate sockets (also referred to as "ports") on multimeter. For most multimeters, the black probe should be plugged into the socket labeled "COM," and the red probe into the socket labeled with a "V" (it might also have some other symbols).
2. Choose the appropriate voltage setting on multimeter's dial. Remember that most battery-powered circuits will have direct current.. If working with a manual-ranging multimeter, estimate the range need based on the battery (or batteries) powering your circuit. For example, if circuit is powered by a single 9V battery, it probably doesn't make sense to select the setting for 200V, and 2V would be too low. If available, would want to select 20V.
3. Touch the probe tips to your circuit in parallel with the element you want to measure voltage across. For example, Figure shows how to measure the voltage drop across a light bulb powered by the battery. Be sure to use the red probe on the side connected to the positive battery terminal, and the black probe on the side connected to the negative battery terminal (nothing will be harmed if one get this backwards, but voltage reading will be negative).

Figure. Measuring voltage across a lightbulb by attaching the multimeter probes in parallel. Current flow  is represented by the yellow arrows. In voltage-measurement mode, the multimeter's resistance is very high,  so almost all of the current flows through the lightbulb, and the multimeter does not have a big impact on  the circuit. Notice how the knob has been set to measure DC voltage (DCV) and the red probe is plugged  into the correct port for measuring voltage (labeled "VΩ" because it is also used to measure resistance).

4. If  multimeter is not auto-ranging, one might need to adjust the range. If  multimeter's screen just reads "0," then the range you have selected is probably too high. If the screen reads "OVER," "OL," or "1" (these are different ways of saying "overload"), then the range you have selected is too low. If this happens, adjust range up or down as necessary. 

Resistance:

Resistance is the measure of electrical "friction" as electrons move through a conductor. It is measured in the unit of the "Ohm," that unit symbolized by the capital Greek letter omega (Ω).

INSTRUCTIONS

Set your multimeter to the highest resistance range available. The resistance function is usually denoted by the unit symbol for resistance: the Greek letter omega (Ω), or sometimes by the word "ohms." Touch the two test probes of meter together. Then, the meter should register 0 ohms of resistance. If one using an analog meter, will notice the needle deflect full-scale when the probes are touched together, and return to its resting position when the probes are pulled apart. The resistance scale on an analog multimeter is reverse-printed from the other scales: zero resistance in indicated at the far right-hand side of the scale, and infinite resistance is indicated at the far left-hand side. There should also be a small adjustment knob or "wheel" on the analog multimeter to calibrate it for "zero" ohms of resistance. Touch the test probes together and move this adjustment until the needle exactly points to zero at the right-hand end of the scale.

Although your multimeter is capable of providing quantitative values of measured resistance, it is also useful for qualitative tests of continuity: whether or not there is a continuous electrical connection from one point to another. One can, for instance, test the continuity of a piece of wire by connecting the meter probes to opposite ends of the wire and checking to see the the needle moves full-scale. What would we say about a piece of wire if the ohmmeter needle didn't move at all when the probes were connected to opposite ends?

Digital multimeters set to the "resistance" mode indicate non-continuity by displaying some non-numerical indication on the display. Some models say "OL" (Open-Loop), while others display dashed lines.Connect the meter's test probes across the resistor as such, and note its indication on the resistance scale:

The needle points very close to zero, you need to select a lower resistance range on the meter, just as you needed to select an appropriate voltage range when reading the voltage of a battery.

If one using a digital multimeter, should see a numerical figure close to 10 shown on the display, with a small "k" symbol on the right-hand side denoting the metric prefix for "kilo" (thousand). Some digital meters are manually-ranged, and require appropriate range selection just as the analog meter. If yours is like this, experiment with different range switch positions and see which one gives you the best indication.

Note ....When touch the meter probes to the resistor terminals, try not to touch both probe tips to fingers. If one do, he will be measuring the parallel combination of the resistor and your own body, which will tend to make the meter indication lower than it should be! When measuring a 10 kΩ resistor, this error will be minimal, but it may be more severe when measuring other values of resistor.

You may safely measure the resistance of your own body by holding one probe tip with the fingers of one hand, and the other probe tip with the fingers of the other hand.

Current

Current is the measure of the rate of electron "flow" in a circuit. It is measured in the unit of the Ampere, simply called "Amp," (A).

INSTRUCTIONS

OR.............................................................................

The most common way to measure current in a circuit is to break the circuit open and insert an "ammeter" in series (in-line) with the circuit so that all electrons flowing through the circuit also have to go through the meter. Because measuring current in this manner requires the meter be made part of the circuit, it is a more difficult type of measurement to make than either voltage or resistance.

Some digital meters, like the unit shown in the illustration, have a separate jack to insert the red test lead plug when measuring current. Other meters, like most inexpensive analog meters, use the same jacks for measuring voltage, resistance, and current.

When an ammeter is placed in series with a circuit, it ideally drops no voltage as current goes through it. In other words, it acts very much like a piece of wire, with very little resistance from one test probe to the other. Consequently, an ammeter will act as a short circuit if placed in parallel (across the terminals of) a substantial source of voltage. If this is done, a surge in current will result, potentially damaging the meter:

Caution:

Ammeters are generally protected from excessive current by means of a small fuse located inside the meter housing. If the ammeter is accidently connected across a substantial voltage source, the resultant surge in current will “blow” the fuse & render the meter incapable of measuring current until the fuse is replaced. Be very careful to avoid this scenario!

Conclusion (while measuring Voltage & Current Of a Circuit)..... 

L298 MOTOR Driver

L298 IC:

Description:

A very popular and reasonably priced all-in-one H-bridge motor driver is the L298. It can control two motors, not just one. It can handle 2 amps per motor, though to get the maximum current be sure to add a heat sink. The L298 has a large cooling flange with a hole in it, making it easy to attach a homebrew metal heat sink to it.If there’s a downside to the L298 it’s that it comes in a special “Multiwatt 15” package, with 15 offset pins that don’t match the standard 0.100" spacing of breadboards. But with care, the pins can be rebent as needed. Or you may prefer to simply get a breakout board for the L298, which is a small circuit board with holes drilled in it to accept the chip. You then plug the breakout board into your breadboard. Problem solved.The schematic below shows a basic connection diagram for controlling two motors using the L298 motor bridge IC. There are three input pins for each motor: Input1, Input2, and Enable1 controls Motor1. Input3, Input4, and Enable2 controls Motor2. The motors connect to Output1/Output2 and Output3/Output4, as shown.

The L298 uses two different supply voltages. The voltage on pin 9 powers the chip itself and should be 5 volts. The voltage on pin 4 supplies the motors, and it can be up to 46 volts.

Let’s look at how to control just one of the motors, Motor1. In order to activate the motor, the Enable1 line must be HIGH. You then control the motor and its direction by applying a LOW or HIGH signal to the Input1 and Input2 lines, as shown in this table.

Input1	Input2	Action
LOW	LOW	Motor breaks and stops*
HIGH	LOW	Motor turns forward
LOW	HIGH	Motor turns backward
HIGH	HIGH	Motor breaks and stops*

* To coast a motor to a slower stop, apply a LOW signal to the Enable1 line.

The L298 does not have built-in protection diodes, so you’ll need to add those. The datasheet for the L298 specifies “fast recovery” 1-amp diodes; an inexpensive selection is the 1N4933, available from most online electronic parts outlets.

L298 based Motor Driver

Fig. of Motor Driver

Features

·         Maximum motor supply voltage: 46V

·         Maximum motor supply current: 2A per motor

·         Current Sense for each motor

·         Heat sink for better performance

·         Power-On LED indicator

 Using the board to drive motor

Motor driving is extremely simple with the board. The board has two ChannelsA and B. It has 2 inputs and 2 corresponding outputs for each Channel. Each channel also has an enable pin and a sense pin. The Input pins are the labelled as INP A and INP B. The enable pin is labeled As EN A and EN B, and the sense pin is labelled as SNS A and SNS B.To drive a DC motor in a particular channel, the enable pin of the Channel has to be supplied with a logic high (+5V) signal. Then, a logic high signal has to be supplied to the input pins to control the direction of the motor. Supplying logic high to any one of the input pins will drive the DC Motor in one direction. On supply logic high to the other Input pin, the motor will run in the opposite direction. Supplying logic high to both input pins will brake the rotation of the motor and Supplying a logic low (0V or Gnd) signal to both the input pins will allow the DC motor to rotate freely.The sense pin can be used to sense and limit the amount of current the motor in corresponding channel is consuming. By default this option is not enabled on the board and the sense pin is directly connected to GND through a jumper.

 Internal and external logic supply for the board

   

The L298 requires an input voltage of 5V for its operation. The board has an on board 5 V regulator (LM7805) for the same. It takes the motor input voltage and regulates it to 5V. The regulated voltage can also be supplied to external circuits and can be tapped through the 5V and Gnd header

The on board voltage regulator can work on a maximum input voltage of 35 V. If you wish to drive motors with voltages greater than 35 V, you will have to supply external 5 V for the board, and cut of the input supply to the on board regulator. This will prevent it from getting damaged due to a high input voltage. You can do this by de-soldering the jumper on the bottom side of the board between Pin 1 of the voltage regulator and the+ve Input Voltage pin.

Advantages of L298 over L293

Reason of Choosing L298 Motor Driver 

The L298 chip is the bigger brother to the L293 chip (a popular small-motor driver IC), but the L298 handles more current, and more voltage - just what you need for those robots that need more power!

One of the first realizations in robotics is that making something move isn’t an easy task. There are many ways to strengthen (”buffer”) a signal so it’s strong enough to drive a large load like a motor. Transistor H bridge circuits, buffer chips, and dedicated motor driving chips are all suitable candidates, with their own benefits and

limitations.

We’re using the well-proven L298 for this design, as it has practically all the features that r need in a good motor driver, including thermal-shutdown, meaning that it will slow down and stop if overloaded (rather than melting down in a catastrophic manner!).

Adding a low-drop out regulator lets you tap off 5V for any other circuitry you may want to drive, and the indicator LEDs are always very useful when monitoring the behaviors of circuit.

Tech Spec:-

L298 has current capacity of 2A per channel @ 45V compared to 0.6 A @ 36 V of a L293D. L293D’s package is not suitable for attaching a good heat sink, practically you can’t use it above 16V without frying it. L298 on the other hand works happily at 16V without a heat sink, though it is always better to use one.

There are several versions of the 16 pin L293s.

The 293D is a 600 ma. 16 pin DIP that has on chip suppressor diodes. 

The 293B is a 1 amp 16 pin DIP that does not have on chip diodes.

For ease of circuit use the L293 is much easier to use due to is dip package, and the L298 is a right bugger of a package to route the pins out from, but it is a bigger driver and will handle more current. it also works very well when used with the L297 chip.

L293D MOTOR DriVER

             L293D DIP16 Package

Description:-

L293D is a typical Motor driver or Motor Driver IC which allows DC motor to drive on either direction. L293D is a 16-pin IC which can control a set of two DC motors simultaneously in any direction. It means that you can control two DC motor with a single L293D IC. Dual H-bridge Motor Driver integrated circuit (IC).The l293d can drive small and quiet big motors as well

capable of driving high voltage motors using TTL 5V logic levels. They can drive 4.5V up to 36V at 1A continuous output current!

L293D Connections

L293D is a 16 pin IC which comes in a DIP Package. Its pin configuration is shown below.

              L293D Pin Configuration

Now let’s have a look at its connections for bidirectional motor control.

                L293D Based Motor Driver

In this way, we can have bidirectional control over two motor. Let’s have a summary of connections:

o    There are two enable (EN) pins, pin 1 and pin 9. Pin 1 EN enables the motor M1 whereas pin 9 EN enables motor M2.

o    Connect motor M1 across OUTPUT1 and OUTPUT2 i.e. across pins 3 and 6.

o    Connect motor M2 across OUTPUT3 and OUTPUT4 i.e. across pins 11 and 14.

o    The inputs for motor M1 is given across INPUT1 and INPUT2 i.e. across pins 2 and 7.

o    The inputs for motor M2 is given across INPUT3 and INPUT4 i.e. across pins 10 and 15.

o    Connect GROUND pins 4, 5, 12 and 13 to ground.

o    Connect pin 16 to Vcc (=5V) and pin 8 to Vs (battery, 4.5V~36V).

As per the diagram, the inputs of motor M1 are M1-A and M1-B, whereas inputs of motor M2 are M2-A and M2-B.

Now consider the following cases for motor M1:

o    M1-A = 1 and M1-B = 0 → M1 moves clockwise (say). Then

o    M1-A = 0 and M1-B = 1 → M1 moves counter-clockwise.

o    M1-A = 0 and M1-B = 0 → M1 stops.

o    M1-A = 1 and M1-B = 1 → M1 stops.

Similar cases can arise for motor M2:

o    M2-A = 1 and M2-B = 0 → M2 moves clockwise (say). Then

o    M2-A = 0 and M2-B = 1 → M2 moves counter-clockwise.

o    M2-A = 0 and M2-B = 0 → M2 stops.

o    M2-A = 1 and M2-B = 1 → M2 stops.

Suppose if you need to control only one motor at a time, you need to enable that particular EN pin. Enabling both pins at the same time will drain your battery unnecessarily.

Concept

It works on the concept of H-bridge. H-bridge is a circuit which allows the voltage to be flown in either direction. As you know voltage need to change its direction for being able to rotate the motor in clockwise or anticlockwise direction, Hence H-bridge IC are ideal for driving a DC motor.

In a single l293d chip there two h-Bridge circuit inside the IC which can rotate two dc motor independently. Due its size it is very much used in robotic application for controlling DC motors. Given below is the pin diagram of a L293D motor controller.

There are two Enable pins on l293d. Pin 1 and pin 9, for being able to drive the motor, the pin 1 and 9 need to be high. For driving the motor with left H-bridge you need to enable pin 1 to high. And for right H-Bridge you need to make the pin 9 to high. If anyone of the either pin1 or pin9 goes low then the motor in the corresponding section will suspend working. It’s like a switch.

Working of L293D

The there 4 input pins for this l293d, pin 2,7 on the left and pin 15 ,10 on the right as shown on the pin diagram. Left input pins will regulate the rotation of motor connected across left side and right input for motor on the right hand side. The motors are rotated on the basis of the inputs provided across the input pins as LOGIC 0 or LOGIC 1.

In simple you need to provide Logic 0 or 1 across the input pins for rotating the motor.

L293D Logic Table

Lets consider a Motor connected on left side output pins (pin 3,6). For rotating the motor in clockwise direction the input pins has to be provided with Logic 1 and Logic 0.   

• Pin 2 = Logic 1 and Pin 7 = Logic 0 | Clockwise Direction

• Pin 2 = Logic 0 and Pin 7 = Logic 1 | Anticlockwise Direction

• Pin 2 = Logic 0 and Pin 7 = Logic 0 | Idle [No rotation] [Hi-Impedance state]

• Pin 2 = Logic 1 and Pin 7 = Logic 1 | Idle [No rotation]

In a very similar way the motor can also operated across input pin 15,10 for motor on the right hand side.