White Line Follower

1.    INTRODUCTION

   

        

                Line follower is a vehicle or robot that can follow a path. The path can be visible like a white line on a black surface. Sensing a line and maneuvering the vehicle to stay on course, while constantly correcting wrong moves using a feedback mechanism forms a simple yet effective closed loop system. The line follower has a classic introductory design and requires a minimal amount of resources. These systems can use simple digital or analog control systems and are highly visual and entertaining to watch.

This project is intended to showcase basic sensor design and robot control systems in the form of a small autonomous vehicle which must follow a white line over a black surface. As a programmer we get an opportunity to teach the vehicle how to follow the line thus giving a human like property of responding to stimuli. A line follower sensor circuit consists of infrared LEDs. It works by illuminating a surface with infrared light; the sensor then picks up the reflected infrared radiation and, based on its intensity, determines the reflectivity of the surface in question. Light-colored surfaces will reflect more light than dark surfaces, resulting in their appearing brighter to the sensor. This allows the sensor to detect a dark line on a pale surface, or a pale line on a dark surface. We can use a line follower to help the vehicle navigate along a marked path, or in any other application involving discerning the boundary between two high-contrast surfaces.

                                       

2. BLOCK DIAGRAM

Figure.1 Block Diagram

         

3. BLOCK DIAGRAM EXPLANATION

           3.1 LIGHT SOURCE                                            

           A light source is used in the system in order to provide a path for the robot. The black surface absorbs the light and the white surface reflects it, this is the basic concept behind sensing mechanism. We can use LED, IRLED etc as a light source.

          3.2 WHITE TRACK

            It is a path that can be visible like a white line over a black surface. This can be done by painting a black surface with white color and vice versa.  

                  

Figure.2   White track

          3.3 LIGHT DETECTOR

            The light source continuously emits white light; then the Light detector picks up the reflected light and, based on its intensity, determines the reflectivity of the surface. White surface reflects lights completely and black surface    absorbs it.

            The electrical resistivity of certain materials changes when exposed to light and they are known as photosesistive or photoconductive materials. All semiconductors are photoresistive in nature and their resistivity falls when light is incident on them. The effect is noticeable in selenium, silicon and germanium. Also, compounds such as lead sulphide, activated polycrystalline cadmium sulpho selinide exhibit this property and they are used as basic materials for the construction of photoconductive cells. The resistivity is high in dark and it may

change by three decades for a change of light intensity by three decades. Here we use light dependent resistors (LDR) as the light detectors.

           

Figure.3  Commercially used LDRs

          3.4 SWITCHING CIRCUITS                                              

            Different types of switching circuits are used today such as mechanical switching circuits, electronic switching circuits etc.  Mechanical switching circuits have several demerits compared to electronic switching circuits. The advantages of electronic switching circuits include high operating speed, minimum wear and tear, long life etc.

          Transistor is an electronic device which can be used for switching purpose. Here we use transistor switches.

          3.5 DC MOTOR

          An Electric motor is a machine, which converts electric energy into mechanical energy. Its action is based on the principle that when a current carrying conductor is placed in a magnetic field , it experiences a mechanical force whose direction is given by Fleming’s Left Hand rule and whose magnetic field is given by F=BIl Newton . Where F is the force acting on the current carrying conductor, B is the magnetic field intensity, I is the current through the conductor and l is the length of conductor. Constructionally , there is no basic

difference between a DC generator and a DC motor. In fact, the same DC machine can be used interchangeably as a generator or as a motor. Torque is defines as rotational effect of  force.

                      

                                  

Figure.4   Dc motor

          

                                   

4. CIRCUIT DIAGRAM

Figure.5 Circuit Diagram

5. CIRCUIT DIAGRAM EXPLANATION

         The LED emits light when the power is on. A series resistor is used to limit the current through the circuit. It is used not to exceed the current to the upper limit. When both the sensors (LDR s) are placed on the black surface both motors will rotate in equal speed. When the sensor is kept on a black surface the light reaching on  the  LDR will be minimum. The resistance of the LDR decreases as incident light increases. Here no light is received by the LDR , so, the resistance is  maximum. Hence   voltage at the basis of transistors Q1 and Q2 to cut off. So the voltage at the bases of Q3 and Q4 will be equal to the collector voltages of Q1 and Q2 respectively. Which is greater than the transistors .that is base collector junction and base emitter junction.

         Hence the transistors Q3 and Q4 are driven in saturation ,and the current slightly less than the saturation current will flow through the output circuit of Q3 and Q4. This drives both the dc motors in equal speed and the robot follow a straight line path.

         When the robot reaches a curved path which bends towards right the right LDR reaches above the white line. The sensor facing white surface receives more intense light. Then the resistance of  the LDR decreases. Hence base of the transistor Q2 gets sufficient voltage to drive the transistor in to saturation. So the voltage at the collector of the transistor Q2 is Vsat, which is not enough to drive the power transistor Q4 in to saturation. There for no current flows through the output circuit to drive the motor. Consider the sensor facing the black surface it receives minimum amount of light. So the resistance of LDR becomes maximum.  The voltage at the base of transistor Q1 will be minimum. It makes the transistor Q1 to cut off. So the voltage at the base of Q3 will be equal to the collector voltage of Q1 which is greater than the voltage required to forward bias the two junctions in the transistor. Hence the transistor Q3 is driven in to saturation and the current slightly less than the saturation current will flow though the output

circuit of Q3.It drives the left motor. Here the right motor stop rotating while the left motor keeps on rotating. So the robot makes a right turn. In this manner robot follows the white curves and straight path.

6. COMPONENTS LIST

Sl No:	COMPONENTS NAME	SPECIFICATION	NUMBERS
1.	Transistors	BC 548	2
		SL 100	2
2.	Resistors	1k	2
		220 ohm	1
3.	Variable resistor (pot)	10 k pot	1
4.	LDR	CdS Photoconductive  Cell or Photoresistor	2
5.	LED	White LED	2
6.	Motor	Low rpm dc motor	2
7.	Battery	9 volt	3

7.   PCB FABRICATION METHODE

           7.1 PCB PREPARATION

       You need to generate a positive (copper black) UV translucent art work film. You will never get a good board without good art work, so it is important to get the best possible quality at this stage. The most important thing is to get a clear sharp image with a very solid opaque black. Art work is done using ORCAD software. It is absolutely essential that your PCB software prints holes in the middle of pads, which will act as centre marks when drilling. It is virtually impossible to accurately hand-drill boards without these holes. If you are looking to buy PCB software at any cost level and want to do hand-prototyping of boards before production, check that this facility is available when defining pad and line shapes, the minimum size recommended (through-linking holes) for reliable result is 50 mil, assuming 0.8mm drill size; 1 mil=(1/1000)^th  of an inch. You can go smaller drill sizes, but through linking will be harder. 65 mil round or square pads for normal components.

Figure.6   Copper clad laminate:

ICs, with 0.8 mm hole, will allow a 12.5mil, down to 10mil if you really need to. Center-to-centre spacing of 12.5 mil tracks should be 25 mil-slightly less may b possible if your printer can manage it. Take care to preserve the correct diagonal track-track spacing on mitered corners; grid is 25 mil and track width 12.5mil. The art work must be printed such that the printed side is in contact with PCB surface when exposing, to avoid blurred edges. In practice, this means that if you design the board as seen from the component side, the bottom (solder side) layer should be printed the ‘correct’ way round, and top side of the double-sided board must be printed mirrored.

          7.2 ETCHING

            Ferric chloride etchant is a messy stuff, but easily available and cheaper than most alternatives. It attacks any metal including stainless steel. So when setting up a PCB etching area, use a plastic or ceramic sink, with plastic fitting and screws wherever possible, and seal any metal screws with silicon. Copper water pipes may be splashed or dripped-on, so sleeve or cover them in plastic; heat-shrink sleeve is great if you are installing new pipes. Fume extraction is not normally required, although a cover over the tank or tray when not in use is a good idea. You should always use the hex hydrate type of ferric chloride, which should be dissolved in warm water until saturation. Adding a teaspoon of table salt helps to make the etchant clearer for easier inspection. Avoid anhydrous ferric chloride.

            It creates a lot of heat when dissolved. So always add the powder very slowly to water; do not add water to the powder, and use gloves and safety glasses. The solution made from anhydrous ferric chloride doesn’t etch at all, so you need to add a small amount of hydrochloric acid and leave it for a day or two. Always take extreme care to avoid splashing when dissolving either type of ferric chloride, acid tends to clump together and you often get big chunks coming out of the container and splashing into the solution. It can damage eyes and permanently stain clothing. If you are making PCBs in a professional environment where time is money you should get a heated bubble-etch tank. With fresh hot ferric chloride,

the PCB will etch in well under 5 minutes. Fast etching produces better edge-quality and consistent line widths. If you aren’t using a bubble tank, you need to agitate frequently to ensure even etching. Warm the etchant by putting the etching tray inside a larger tray filled with boiling water.

          7.3 DRILLING

Figure.7 Drilling of PCB

If you have fiber glass (FR4) board, you must use tungsten carbide drill bits. Fiber glass eats normal high-speed steel (HSS) bits very rapidly, although HSS drills are alright for older larger sizes (> 2mm). Carbide drill bits are available as straight-shank or thick-shank. In straight shank, the hole bit is the diameter of the hole, and in thick shank, a standard size (typically about 3.5 mm) shank tapers down to the hole size. The straight-shank drills are usually preferred because they break less easily and are usually cheaper. The longer thin section provides more flexibility. Small drills for PCB use usually come with either a set of collets of various sizes or a three-jaw chuck. Sometimes the 3-jaw chuck is an optional extra and is worth getting for the time it saves on changing collets. For accuracy, however, 3-jaw chucks are not brilliant, and small drill sizes below 1 mm quickly formed grooves in the jaws, preventing good grip. Below  1mm, you should use collets, and buy a few extra of the smallest ones;

Keeping one collect per drill size as using a larger drill in a collet will open it out and it no longer grips smaller drills well. You need a good strong light on the board when drilling, to ensure accuracy. A dichroic halogen lamp, under run at 9V to reduce brightness, can be mounted on a microphone gooseneck for easy positioning. It can be useful to raise the working surface above 15 cm above the normal desk height for more comfortable viewing. Dust extraction is nice, but not essential and occasional blow does the trick! A foot-pedal control to switch the drill ‘off’ and ‘on’ is very convenient, especially when frequently changing bits. Avoid hole sizes less than 0.8 mm unless you really need them. When making two identical boards, drill them both together to save time. To do this, carefully drill a 0.8 mm whole in the pad near each corner of each of the two boards, getting the center as accurately as possible. For larger boards, drill a hole near the centre of each side as well. Lay the boards on the top of each other and insert a 0.8 mm track pin in two opposite corners, using the pins as pegs to line the PCBs up. Squeeze or hammer the pins into boards, and then into the remaining holes. The two PCBs are now ‘nailed’ together accurately and can be drilled together.

8.  SOLDERING

Figure.8 Soldering

Soldering is the joining together of two metals to give physical bonding and good electrical conductivity. It is used primarily in electrical and electronic circuitry.

Solder is a combination of metals, which are solid at normal room temperatures and become liquid between 180 and 200 degree Celsius. Solder bonds well to various metals, and extremely well to copper. Soldering is a necessary skill you need to learn to successfully build electronics circuits. To solder you need a soldering iron. A modern basic electrical soldering iron consists of a heating element, a soldering bit (often called a tip), a handle and a power cord. The heating element can be either a resistance wire wound around a ceramic tube, or a thick film resistance element printed on to a ceramic base. The element is then insulated and placed into a metal tube for strength and protection. This is then thermally insulated from the handle. The heating element of soldering iron usually reaches temperatures of around 370 to 400 degree Celsius (higher than need to melt the solder). The strength or power of a soldering iron is usually expressed in watts. Irons generally used in electronics are typically in the range of 12 to 25 watts. Higher powered iron will not run hotter. Most irons are available in a variety of voltages; 12V, 24V, 115V and 230V are most popular. Today most laboratories and repair shops use soldering irons, which operate at 24V.

You should always use this low voltage where possible, as it is much safer. For advanced soldering work, you will need a soldering iron with temperature control. In this type of soldering irons, the temperature may be usually set between 200 and 450 degree Celsius.

            Many temperature control soldering iron designed for electronics have a power rating of around 40 to 50 watt. They will heat fast and give enough power for operation, but are mechanically small.

            You will occasionally see gas-powered soldering irons which use butane rather than the main electrical supply to operate. They have a catalytic element which once warmed up, continues to glow hot when gas passes over them. Gas powered soldering irons are designed for occasional ‘on the spot’ used for quick repairs, rather than for main stream construction or for assembly work.

            Currently, the best commonly available, workable, and safe solder alloy is 63/37. That is, 63% lead, 37% tin. It is also known as eutectic solder. Its most desirable characteristic is that it solids (‘pasty’) state, and its liquid state occur at the same temperature -361 degree Fahrenheit. The combination of 63% lead and 37% tin melts at the lowest possible temperature. Nowadays there is tendency to move to use lead free solders, but it will take years until they catch on normal soldering work. Lead free solders are nowadays available, but they are generally more expensive or harder to work on than traditional solders that they have lead in them.

      The metals involved are not the only things to consider in a solder. Flux is vital to a good solder joint. Flux is an aggressive chemical that removes oxide and impurities from the parts to be soldered. The chemical reactions at the point(s) of connection must take place for the metal to fuse. RMA type flux (Rosin Mildly Active) is the least corrosive of the readily available materials, and provides an adequate oxide removal.

In electronics, a 60/40 fixed core solder is used. This consists of 60% lead and 40% tin, with flux cores added to the length of solder.

There are certain safety measures which you should keep in mind when soldering. The tin material used in soldering contains dangerous substances like lead (40-60% of typical soldering tins are lead and lead is poisonous). Also the various fumes from the soldering flux can be dangerous. While it is true that lead does not vaporize at the temperature at which soldering is typically done.

            When soldering, keep the room well ventilated and use a small fan or fume trap. A proper fume trap of a fan will keep the most pollution away from your face. Professional electronic workshops use expensive fume extraction systems to protect their workers. Those fume extraction devices have a special filter which filters out the dangerous fumes. If you can connect a duct to the output from the trap to the outside, that would be great.

            Always wash hands prior to smoking, eating, drinking or going to the bathroom. When you handle soldering tin, your hands will pick up lead, which needs to be washed out from it before it gets to your body. Do not eat, drink or smoke while working with soldering iron. Do not place cups, glasses or a plate of food near your working area.

Wash also the table sometimes. As you solder, at times there will be a bit of spitting or sputtering. If you look you will see tiny balls of solder that shoot out and can be found on your soldering table.                                

                         

         

9. PCB LAYOUT

 9.1. COMPONENT SIDE VIEW

Figure.9 Component Side View

9.2 SOLDER SIDE VIEW

Figure.10 Solder Side View

10. ADVANTAGES

·         Low cost.

·         Easy to make.

·         Easy To Handle.

·         It is portable.

·         Requires minimum materials.

11. DISADVANTAGES

·         Slow speed.

·         Instability on different line thickness.

·         Instability on hard angles.

·         Lack of decision making capacity at the junctions.

12. APPLICATIONS

·         Industrial automated equipment carriers.

·         Automated vehicles.

·         Tour guides in museum and other similar applications.

·         Transfer luggage in airports. 

13. CONCLUSION

           

          White line followers are the basic forms of autonomous robots. The usual robots in this category are complex, costly, bulky and after all slow.

            The prototype which we have developed is a simple demonstration of how simple a robot can be. We have brought up an alternative to the usual ones. Ours is a better, efficient and fast version of the same. The tracking is faster with lesser response time.

             Hence we have succeeded in making a robot that is more efficient and less costly than its rivals.

14. FUTURE SCOPE

            There are cases where smarter versions of line followers are used to deliver mail within an office building and deliver medications in a hospital.
the technology has been suggested for running buses and other mass transit systems, and may end up as part of autonomous cars navigating the freeway.

APPENDIX