Blog Entry

Build Your Own Transistor Based Mobile Line Follower Robot (LFR) – First Part

July 11, 2009 by , under Robotics.

The mobile line follower robot is a type of mobile robot with only has one specific task which is to follow the line made with black tape over the white background or vise verse. The LFR perhaps is one of the most popular robot build by the roboticists. What makes this LFR is so popular, I think because of its simplicity and yet it could be used as the teaching tools of how we could implement the industrial standard control system such as the PID (Proportional Integral Deferential) control system on this robot. Another factor probably is the increase of the LFR annual tournament conducted in many countries.

Build Your Own Transistor Based Mobile Line Follower Robot (04)

The basic principal of the line follower robot actually almost the same as the light follower robot, but instead of tracking the light the LFR sensor is used to track the line, therefore by differentiating the line color and it’s surrounding (black over white or vise verse) any light sensitive sensor could be used to navigate the mobile robot to follow this track.

Base on the above fact, I designed the simplest possible electronics circuit that use the navigation principal shown above to track the black tape line.

Build Your Own Transistor Based Mobile Line Follower Robot (05)

The 2N3904 NPN Bipolar Junction Transistor (BJT) is designed to operate as the current gainer amplifier; this means we operate the 2N3904 transistor in its linear region. The advantages of using the transistor in its linear region is; the transistor collector current passed through the DC motor will varying according to the base current which controlled by the LDR (Light Dependent Transistor) and 10 K trimmer potentiometer (trimpot). Therefore the current through the DC motor will vary according to the light intensity received by the LDR.

Using this simple principal we could easily used this circuit to track the black tape by locating the LDR and the white LED in such a way that the LDR will receive less light from the white LED when the LDR position right on top of the black tape and this will make the DC motor to turn slowly (less collector current). When the LDR position outside the black tape (on the top of the white background) the LDR will receive more light from the white LED; this will make the motor to turn faster (more collector current).

The trimpot is use to adjust the DC motor speed, while the 1N4148 diode is use to protect the transistor again the EMF (Electromotive Force) generated by the DC motor inductor when its switch off. The key of successfully building this circuit is heavily depend on the geared DC motor we choosed.

Build Your Own Transistor Based Mobile Line Follower Robot (03)

You have to choose the geared DC motors which rated 5 volt that have low power consumption (small current) as the 2N3094 transistor only allowed max 100 mA current on its collector (you could replace it with 2N2222A transistor, max 800mA) and try to use a low RPM (rotation per minute) geared DC motor (remember must be the geared DC motor). The lower RPM is required here because the LDR has a slow response comparing to other light sensitive component (e.g. photo transistor), so the Line Follower Robot could keep follow the black track line. You could always experiment with your own geared DC motor speed on different track’s route by adjusting the 10 K Ohm trimport.

One of disadvantage using the transistor on its linear region to control the DC motor’s speed is the power dissipation (power loss as heat) on the transistor especially if we use large power DC motor, the common and efficient method to control the motor’s speed is to use the PWM (pulse width modulation) which make the transistor on and off rapidly; but for the geared DC motor used in this Line Follower Robot project we simply take advantage of the transistor in its linear region to change its speed (i.e. by changing the transistor collector current). You could read more information about building the PWM based Line Follower Robot on “The LM324 Quad Op-Amp Line Follower Robot with Pulse Width Modulation” project on this blog

This line follower robot use what is called the “differential drive” steering method, which use two independent motor mounted in fixed positions on the left and right side of robot’s chassis. This mean by slowing the rotation speed of the left DC motor will make the robot to arc to the left and slowing the rotation speed of the right DC motor will make the robot to arc to the right. If both motor rotate at the same speed than the robot will simply go straight as shown on this following picture.

Therefore by arching to the left and to the right or go straight the robot could easily follow the black line track. As you know how this two transistors line follower robot circuit works, now its time to build the robot chassis.

The LFR Chassis Construction

The LFR construction in this tutorial is very simple as I just use a 1 mm cardboard for the main body construction and use caster (the third wheel) made from bead and paperclip as shown on my previous posted blog Building BRAM your first Autonomous Mobile Robot using Microchip PIC Microcontroller.

By using this easy to handle construction material hoping you could easily build this Line Follower Robot, these following pictures show how to assembly all these parts together.

Build Your Own Transistor Based Mobile Line Follower Robot (02)

Build Your Own Transistor Based Mobile Line Follower Robot (01)

I use double tape to hold the 3 x AA (4.5 volt) battery holder and the micro geared DC motor (now you understand how important this double tape to the robot’s builder); the DC motor also is reinforced with the plastic cable’s ties. The electronics component is soldered on the 18 x 38 mm prototype PCB and I just use the duct tape to hold the LDR and LED together as shown on the above circuit. To make it more interesting I put one  three colors auto flashing LED for the indicator.

Bellow is the complete list of material and electronics component used to build this line follower robot:

1. Thick paper (1 mm), double tape, duct tape, plastic cable’s ties
2. One paper clip and bead for the caster (the third wheel)
3. Adequate Bolts and Nuts
4. One 3 x AA Battery holder and 3 x AA (1.5 Volt Alkaline) Battery
5. Two micro geared DC motor rated 5 volt, unloaded RPM < 50, unloaded current: < 50mA
6. 18 x 38 mm prototype PCB
7. Two 220 Ohm 0.25 watt resistor
8. Two LDR (about 2 ~ 5K Ohm in the bright light and 100K Ohm in the dark).
9. Two 3mm white LED
10. One auto flashing RGB LED with one 220 ohm resistor 0.25 watt (optional)
11. Two 10 K Ohm Trimmer Potentiometer
12. Two 1N4148 Diodes
13. Two 2N3904 or 2N2222A Transistors.

Now it’s time to show the capabilities of this simple and easy to build line follower robot.

The Final Thought

As you’ve seen from the demo video above this two transistors Line Follower Robot sometimes out perform many of the microcontroller based line follower robot designed and for sure using more complex circuit (e.g. the 8-bits microcontroller and the motor controller) and not to mention the microcontroller’s programming; which eventually do the same job as demonstrated by this simple two transistors based line follower robot.

For higher speed line follower robot with more complex track, we need to use the microcontroller, although it’s possible to use just a discrete electronics components but its required more complex circuit which than the microcontroller based solution become more simple and cheap to be used. On my second part of the line follower robot (LFR), we will build the microcontroller’s based LFR which using more advance sensors to track the line compared to this one.

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104 Responses to “Build Your Own Transistor Based Mobile Line Follower Robot (LFR) – First Part”


Comment by RajuDolly.

Thanks a lot again for this fantastic project. Eagerly waiting for 2nd part
Thanks again and again



Comment by robotics.

I can’t get the robot to change speeds, i have followed the instructions to the letter and still no luck. Do you any tips or ideas to help me?


Comment by rwb.

Could not change speed means the transistor is not working properly. Try to disconnect the LDR (transistor’s base lead is open) and see if the motor is still spinning, if it still run then the transistor is bad; if not then try to connect again the LDR and adjust the 10K trimport to it’s maximum value (10K Ohm max) slowly and examine the motor’s speed.


Comment by newbie999.


one question.

do you connect the + and – to the two motors reversely?


Comment by rwb.

Because the motor is placed on the opposite position than positive (+) and the negative (-) voltage will also opposite for the left and right motor; you have to make sure when both left and right motor rotating, they should move the robot forward.


Comment by newbie999.

Thank you. Hope you will show newbies like me
more on this wonderful blog.


Comment by danny.

hi rwb,

your work is really inspiring.i am new to this field.i couldn’t get any geared motor for buiding the LFR using transistor.could you suggest an alternative for that?
yours sincerely,


Comment by rwb.

You should use the geared DC motor which has low RPM in order this LFR circuit to work. The other alternative is to use the modified servo motor where you only use the geared DC motor parts, discarding the servo electronic parts.


Comment by andreejimp.

hi rwb…is the geared micro dc motor available in the local market? I’ve been looking for it for almost a month and still i couldn’t find one..i’ve got only a few weeks to submit this project…thanks a lot rwb


Comment by rwb.

I don’t know for the local market, but you could also use the modified servo motor where you could remove all the electronic servo control section (google it) and use only the geared DC Motor part. The servo motor could be easily found on the R/C (Radio Control) hobbyist store.


Comment by ragubond.

boss, can u pls mail me abt the working of this robot.. more over i tried this using toy motor but the motor is not running at all i changed the transistor too
pls inform me boss it ll b gr8 help to me..


Comment by ragubond.

my id


Comment by rwb.

You could not use toys motor, use the geared dc motor or modified servo motor, you could read my previous comment (#3) regarding how to debug your circuit.


Comment by prasadz101.

what should be the rpm of da motor………i mean which is stable……and efficient

mail me at…


Comment by rwb.

The ideal geared DC motor for this LFR circuit is about 120 RPM or less.


Comment by prathmesh.

hey dude ive got a 12 v low rpm motor i have searched whole of lamington street in mubai but i cant get a 5volt low rpm motor can u suggest me sum alternatives plz i need dis badly


Comment by prathmesh.

ma email id iz plz help me fast dude im in a big mess


Comment by rwb.

You could not use the 12 volt DC motor (used for industry and automotive) with the circuit schema above, usually this kind of motor need bigger current in order to work. For the alternative DC geared motor you could use the modified servo motor (please read my previous comment #10).


Comment by prathmesh.

thanx dude
but the fault is that there is not enough potential drop
built by the resistance of LDRs to cause any variation in the speed of the motor on turnings as the variation is only of 3-4 volts it does not affect the speed of the motor too much[wich is itself of 12v] due to wich its not turning on turns can u suggest me sum alternative or shud i use more LDRs
plz reply dude
thanx in advance


Comment by rwb.

That’s why I’ve said that it won’t work with the schema above, for example the 5 Volt DC motor that I used in this project only draw about 30mA in order to work; which is work perfectly on the schema above. But in your case, you need a proper amplification in order to make your DC motor to work. Remember in the schema above, we operate the transistor in its linear region not as a switch (on/off) and the 2N3904 transistor could be operate with 100mA maximum current, therefore I suggest you to use a proper DC motor if you still want to use just two transistor for the Line Follower Robot (LFR), try to search it on the web there are plenty of them that sell this kind of stuff usually in robotics hobbyist website if you could not found the small DC motor in the local market.


Comment by saurabh anand.

hi! i m new to all this.though hve a bit concept. actually i’m nt getting it right as where to start for a lfr . quite cnfused. moreover not getting the right place to get my materials in kolkata. plzzz help….. rply awaited…….
email id:


Comment by rwb.

You have to read the blog/article and just follow the instruction!


Comment by tonestyle.

hey rwb tanx so much 4dis blog i dun tink u can imagine how much it helps pple like me…..i’m quite new 2 all dis but d simplicity in which u present ur project encourages me to try som of dem out.
i intend to start wit d LFR but i would like to know are dere any ways in which d transistor based lfr can b more robust with extra pecs any suggestion on dat?i would really appreciate ur reply tanx…..


Comment by rwb.

This circuit is depend heavily on the DC motor you use, therefore in order to make this LFR circuit work you need this following DC motor specification:

Use small geared DC motor (sometimes its called micro geared DC motor) with targeted for 5 to 6 volt operation with 120 RPM or less and the operating current of 30 mA to 60 mA. If you follow all the instruction on the article above you should get the same result as the LFR shown on the video.


Comment by shamjoshi.

hi, i’m completely new to robotics so i had two queries.
1. What modifications must be made to the circuit so as to detect a white track on a black background?
2. If the motor rating is 5-6V, 30mA to 60mA and 150rpm, will it be safe to implement in the circuit?

Thanks !


Comment by rwb.

You need to use two stage transistor circuit for each motor, therefore you will need 4 transistors for the robot. My suggestion is to experiment with the schema above before going further. For the DC motor you could try to experiment with it by supplying 4.5 volt (3xAA battery) on it; as it will lower the motor’s RPM.


Comment by richiereynolds.

Hi there, hoping you can clarify a few things from the circuit diagram, I’m not too familiar with electronics.

Where the motros are marked, is this just one pole of the motor that’s connected here and the other pole is connected to ground?

For the variable resistors are, I guess I attach pin 1 to the LDR and pin 2 to the base on the transistor, is that right? What about pin 3? Does it connect to pin 2 or ground or nothing at all?

Thanks, Richard.


Comment by rwb.

Hi Richard, the DC motor poles are connected to the Vcc (4.5 Volt) and Transistor’s Collector (C) terminal. For the trimport (variable resistor); the first pin connected to LDR and the second pin (center pin) connected to the transistor’s base (B) terminal and you could let the third pin open or connected to the second pin.


Comment by richiereynolds.

Ah, I see, thanks very much!


Comment by richiereynolds.

Got it working, well, kind of. Is there a way to adjust this circuit to increase the ratio between the motors? i.e. to get a higher voltage for light and lower for dark than I’m currently getting?

I’ve tried the extremes of the trimports but can only manage very gentle curves.

Mind you, the paper I’m using for the surface I’m driving on is pretty dull i.e. the contrast between it and my black tape could be a lot better so that’s probably my main issue but I’m wondering if I can increase the difference electronically too.

Thanks, Richard.


Comment by rwb.

To enhanced this circuit means we have to use more transistors (hmm,..perhaps I will consider it in my future LFR post). When you use just two transistors the first thing you have to consider is the motor speed, because the LDR sensor responds is slow; therefore you should choose the lowest RPM DC geared motor you could get. The second thing is to maximized the sensors; this means make sure you experiment with the LDR position towards the black line over white surface and make sure the LDR only receive the light from the LED. The last; this simple LFR circuit is not designed to work on a sharp curve. Try to experiment with the different curves until it work for your LFR, you could watch the video where it show the speed and the curve which is suitable for this LFR.


Comment by cheerfulari.

my robot is not dc micro motor and gear motor same??


Comment by rwb.

DC micro motor is just the name (perhaps because of its size). The important is to use geared DC motor where the gear is used to reduce RPM and increase the motor torque.


Comment by venkatesh.

sir, i am a new person to the field of electronics………….so can u pls give me the step by step procedure to construct this LFR………….SO that it will be usefull to me to construct it………..sir pls rply me as soon as possible…………….
my advance hearty thanks to u………..


Comment by rwb.

All the instructions needed to build this LFR is already here. It might be helpful if you also read all the question and answer regarding this LFR. You could also read the comments that I made in this link and watch this LFR version built by djhesit8 in this link


Comment by venkatesh.

thank u for our rply…………………..
when u r going to realise LFR part 2……….


Comment by rwb.

You could read my previous posted blog “Build Your Own Microcontroller Based PID Control Line Follower Robot (LFR) – Second Part” in this link


Comment by cheerfulari.

the motors are working.but it is too heavy and it cannot take the load.thus the motors are spinning but the wheels are not moving.what can i do?


Comment by rwb.

You have to use geared DC Motor and make sure the LFR platform is suitable with the DC Motor capacity.


Comment by venkatesh.

can u provide me a video of construction of this LFR………pls


Comment by rwb.

I only made one video as you’ve seen from this blog. Just follow the picture provided here as this LFR is the simplest one to built.


Comment by cheerfulari.

Hey!!!I am having a problem.I am using a 6v source and because I couldn’t find a 5v motor,i had to use 12v motors.Now the problem is that one of the wheels is making more rotations than the other and as a result,the motor is moving circularly.Secondly,it is detecting almost any light.Please can u reply me the solutions fast.


Comment by rwb.

Make sure you use the same DC geared motors to drive the LFR, also you could adjust the trimport to make them balance. Isolate the LDR from the surrounding light; so it only receive the light from the white LED.


Comment by venkatesh.

can u send me the application of this lfr……….or the related web site about it……. pls……..


Comment by rwb.

The LFR usually is used as a tools to show of how to implement the closed loop control principal found in many industrial in the attractive way and easy to understand.


Comment by venkatesh.

sir i need a brief application of it ………………..sir pls can u send me the details of the application of lfr……….
pls sir i need that for my project……….


Comment by rwb.

You could read my previous posted blog where the full industrial standard Proportional, Integral and Derivative control (PID) is being applied to the LFR here


Comment by venkatesh.

sir i mean that what are the uses of this LFR……………… which field……….how……..for what it is used……..


Comment by rwb.

As I said in my first comment “The LFR usually is used as a tools to show of how to implement the closed loop control principal found in many industrial in the attractive way and easy to understand”. Therefore the “LFR” is one of the application of the closed loop control. Some of the experimental LFR application is to automatically store and take out the goods from shelves in the warehouse; the LFR is controlled by the warehouse management system software through the wireless connection.


Comment by venkatesh.

what is the expense for buliding this LFR?.


Comment by rwb.

The most expensive parts is the DC geared motor, it will cost about USD 20 for two motors with wheels. The LDR, Resistors, Trimports, LEDs, Transistors, Cables, Prototype Boards and 3AA battery holder are about USD 8. Therefore the total cost to build this LFR should be less than USD 30.


Comment by peet.

i hope we can do this!! XD
actually, we are having a project regarding this. i really thank you for the infos you have shared!


Comment by wangui_esther.

hi rwb. I finally started coding with atmega32 with your program simple tutorial with avr the one for blinking leds. the thing is when i connect the stk 500, it keeps giving me an error saying i must have chosen something wrong. is there any additional thing i should do apart from installing avrstudio and win avr like setting some fuses?


Comment by rwb.

How did you connect the atmega32 with STK500? Did you use it as programmer or use the STK500 development board with atmega32 microcontroller on it?


Comment by wangui_esther.

i placed the atmega32 in the stk500 and hit the connect icon on avrstudio4 and chose stk500 as the device and wanted to then download the program onto it. i used a 12v supply and when i switched the stk500 0n there were two green lights and the four leds on on one end lit.


Comment by rwb.

Ok, because this topic is not related anymore within this post, therefore I will email you directly my comment.


Comment by Mike.

Hey rwb Iam a new user for this site, I just viewed your video on Youtube and read your blog, I constructed a two transistor Line follower just like you have written on this page, but the problem is I didn’t get a Micro-motor, so I just fixed the High RPM Toy motor . Its not working, even if I increase the voltage from 4.5V to 9.0V. I need your help solving my problem with this, plz help me , plz tell me if there are any alternatives like Amplifying the current or the voltage ( with the circuit diagrams ) plz. Plz e-mail me with your solution to my e-mail id i.e;
I am waiting for your reply. Bye , n thanks for the line follower, its awesome.


Comment by rwb.

You have to use the geared DC motor for the LFR, since this circuit is designed to be as simple as possible therefore you need to follow the requirement especially for the geared DC motor. You could use any 5-6 volt DC geared motor available on the market such as shown on this following video


Comment by Mike.

Hey thanks rwb, it helped me a lot.
And can u help me in digital electronics ideas like Making a simple calculator using some ICs which just performs the basic operations? plz reply to me.
And one more time thanks for your two transistor line follower robot.


Comment by rwb.

To make a simple calculator you could use microcontroller which connected to LCD and Keypad


Comment by Mike.

Thanks, and But can you please tell about which Microcontroller (some number or name of it), That would be more helpful to me.
Thanks for your reply once again.


Comment by rwb.

You could start with 40 pins 8-bit microcontroller such as Microchip PIC16F887 or Atmel AVR ATmega8515 as you will need plenty of I/O ports for the calculator project


Comment by Mike.

Ok thanks for the information about microcontrollers,
I’ll Work out .
Thanks. Bye.


Comment by preetham.

Hi……thanks for the amazing project
i have a doubt,
will adding more LDR’s help in sensing correctly??


Comment by rwb.

No, it won’t make any improvement!


Comment by yash.

hey this is my first project so plzzz tell where to connect the -ve port of the battery in the circuit diagram!!! plzzz tell me ? ????


Comment by rwb.

The battery negative (-) terminal connect to the GND sign and the battery positive (+) terminal connect to the 4.5 volt sign.


Comment by pramod.

HI,this is Pramod kumar.g from mysore………i could not find dc geared motor n servo motor any where,so can u give me any alternative regarding dat…..pls do reply for my id


Comment by rwb.

You need to use the DC geared motor in order to successful build this LFR


Comment by ranjan.

hi rbw
in the ckt i am using 6-12v geared dc motors they r working too but while working,one part of my ckt sensing correctly but another is not sensing same as first(slowly from very close) ,i ‘ve changed ldr still same problem…..can u help??
i am using 6v supply.


Comment by rwb.

The two sensor circuits should be identical. Try to swap the transistor or/and the DC motor!


Comment by ravi03071991.

cn i noe wat does removing electronic part of servo motor??


Comment by rwb.

The servo motor usually contain the electronics parts and the geared DC motor. You need to carefully remove the electronics parts and connect directly the power leads to the motor, please google it of how to do this modification. My suggestion its easier and cheaper to use an ordinary geared DC motor on this project.


Comment by o2jhoule07.

Good day sir, what if i use a toy’s dc motor and i integrate a gearbox on it, and i change the transistor to BC 639 as said in the info that it can give you up to 1000 mA for the motor to work. is there a possibility on the circuit to work? please reply here as soon as possible. thanks in advance.


Comment by rwb.

Yes you could give it a try; and make sure a gearbox will reduce the DC motor RPM to about 120 or less.


Comment by o2jhoule07.

alright, i absolutely give it a try. thanks a lot sir!


Comment by ravi03071991.

should we include any resistor in series to ldr or else just d ldr is sufficient??


Comment by rwb.

Just follow the schematic, you only need to use 10K trimport and LDR.


Comment by o2jhoule07.

sir, one more question. i followed the schematic diagram and i used 2N3094 transistor and a toy’s DC motor. when i test the circuit, the motor did not start but the lights are working. so i troubleshoot it and i placed a LED instead of the motor as an output test. and i observed that the output for the motor has a low current. my question is if i change the 2N3094 to BC639 Transistor, did you think it can supply a better current so that the motor will work? thanks in advance sir!


Comment by o2jhoule07.

sir, I’ve got a problem, i can’t find any BC639 in the market. how can i run a toy’s DC motor using the 2N3094 transistor? or is there a substitution value for BC639? i think that’s the only choice for me to work this project. again, thanks in advance sir!


Comment by ravi03071991.

what is the purpose of diodes across motors??


Comment by rwb.

The schematic is designed to work with the low current geared DC motor. Most of the toy’s DC motor especially the one that used in tamiya toy race car is consumed more than 1 A, as it specially designed for racing. You need to examine your DC motor current consumption before deciding the transistor type to be used in your LFR.

The diodes across motors is used for EMF protection, you could read more about Using transistor as Switch articles at


Comment by aravind.

wow! this is awesome…. i was lookin out for a follower widout a microcontroller…. tanq for ur post sir!!! am gonna try it out…if any doubts il catch u bak wen i need ur help!!!

gr8 work!!! keep rockin!


Comment by agnes.zhang14.

thank you very much
i’ve tried this project and it works
I used double geared gear box…
and I add TIP41 to the board…
here is the picture
I’ve recorded a video when it walks following the line
post later..


Comment by Amar.

with the same specifications as given…
my motor is not running…
i got a 6v DC micro geared motor i find the circuit was correct but i found that the collector current is not sufficient for the motor to there anything i can do?? can i use two 4.5v setup for more current?? will it affect the circuit??
Thank you in advance :)


Comment by rwb.

Yes you could increase the supply voltage but first you need to measure your own DC motor operating current so it will not exceed the maximum collector current allowed by the 2N3904 transistor (i.e. less than 0.1A).


Comment by Amar.

I have a problem with the light focusing to the LDR could u please brief me.. the sensor setup.. just the way i am supposed to fix the LED and LDR i have a 2 M ohms LDR it works only when the LED is kept sort of perpendicular… ant ways to fix it??
Thank you in advance :)


Comment by rwb.

There are many LDR specification on the market, you should try to get more sensitive LDR (lower resistance) in normal room daylight where it give you about 5K to 20K Ohm and more than 200K in the dark (cover the LDR surface with your finger).


Comment by ankur619.

Sir thanks for the whole tutorial…
But i am gettin a problem with this specification…the robot is working on a simple black line a also is takin a nice turn…but when i make a cross path of a black tape over a path perpendiculary…then the robot stops ….please help me with this…i want to make the robot move over the path…please mail me circuit modifications to be made…
thanks in advance


Comment by rwb.

You need to adjust the trimport or the DC motor to the LDR sensor distance or modify the cross path (i.e. the shape is like “+” sign not “x” sign), so when it cross the black line the DC motor still have the momentum to push the LFR body across the cross black line. Remember this LFR is aimed to use a simple black track line. For more accurate LFR you could read the “The LM324 Quad Op-Amp Line Follower Robot with Pulse Width Modulation” article on this blog


Comment by j-pal.

what was the cost to build this robot?


Comment by rwb.

Please read comment #51


Comment by jyothinath.

If we place some extra sensor in this ckt , will this be able to move easily ? how can we increase the rpm of this motor ?


Comment by rwb.

This is a very simple LFR project i.e. only two transistors which is used for processing the sensor and at the same time driving the geared DC motor, therefore adding extra sensor will change the whole circuit design.


Comment by aravind9948.

when we disconnecting ldrs and keeping a wire instead of ldrs the motors are rotating


Comment by rwb.

Check your LDR. It should give you a low resistance value about 2.000 to 5.000 Ohm when it exposed to the light and more then 80.000 Ohm when on the dark.


Comment by aravind9948.

if more than 5 ohms when exposed to light what should be happen.can i use toy dc motor and it can be converted into a gear dc motor with low rpm


Comment by rwb.

I assumed what you really mean is more than 5000 Ohm, try to adjust the trimport. Sure you could convert the toy DC motor into the gear DC motor (low RPM) if you have the adequate gear box to do it.


Comment by aravind9948.

ya i have.if ldr value is more than 5000 how can i adjust the value can i replace another ldr or can i adjust with the trimport.


Comment by rwb.

This project is heavily depend on a good (sensitive) LDR, therefore you need to find a sensitive LDR in order to successfully build this project.


Comment by aravind9948.

hi rwb
Thanks for the last comment rwb,LDRS are working properly.when i am using toy dc motors there is know rotation of motors,if i am removing motors and keeping the leds there is a response from the leds what is the problem i think there is low power from collecter so can i replace the transistor with “BC 639″ if it work properly


Comment by rwb.

Try to use a geared DC motor with small current e.g. less then 60 mA when operate normally (no load) and use the 2N2222A transistor instead of the BC639 transistor.


Comment by polaris589.

we are now made this project but the problem is that we should applied logic gates.. is it possible to used ic in this circuit? how is that possible? thanks


Comment by rwb.

Yes its possible but that will change the entire electronic circuit schematic and its beyond the purpose of this project. You could read more about the Line follower Robot on “Build Your Own Microcontroller Based PID Control Line Follower Robot (LFR) (Second Part)” and “The LM324 Quad Op-Amp Line Follower Robot with Pulse Width Modulation” articles.