line follower

[zharie]

hi guys,
this is my first time to write in here and i really need your help. I'm in the midst of my line follower circuit project. It is actually a transistor based line follower. I'm using a 2N3904 NPN BJT. Does anyone have an idea on how can I include an IC here. my professor wants me to use LOGIC gates and implement it on the circuit. It should be done without the use of microcontrollers. If you have any schematic diagram it would be of great help. I need to submit it on monday. I hope you could help me.
thank you very much!

 

[stephen87]

you need to contruct a logic truth table which need to switch off/on the transistors (as outputs) by the Infra red led's (as inputs). my line following robot: **broken link removed**

 

[zharie]

how? can you give me an example please?

 

[stephen87]

check this link: Build Your Own Transistor Based Mobile Line Follower Robot (LFR)

 

[DerStrom8]

You say you want to use a chip instead? When I built a line-following robot, I used a 393 comparator. I'm not sure if this is exactly what you want, but it does include a chip. It is the first diagram on site.
I hope this helps!
Der Strom

 

[zharie]

this is actually the exact circuit i'm doing. I don't know where to put the IC because the circuit itself is complete and functioning properly.

 

[zharie]

will I obtain a truth table if I use 393 comparator? what's the main use of comparator in the circuit? how does it functions?

 

[DerStrom8]

this is actually the exact circuit i'm doing. I don't know where to put the IC because the circuit itself is complete and functioning properly.

Are you saying you are already using the comparator? This circuit schematic shows you how to replace the transistors with the 393. What exactly are you looking for?

will I obtain a truth table if I use 393 comparator? what's the main use of comparator in the circuit? how does it functions?

The comparator takes the place of transistors and measures the relative resistance of the LDR sensors. If there is a dark line on a light floor, when the left LDRs sense dark, they will turn off the left motor, causing the robot to turn left. The same goes for the sensors on the right side. Does this make sense?
Der Strom

 

[zharie]

Are you saying you are already using the comparator? This circuit schematic shows you how to replace the transistors with the 393. What exactly are you looking for?



The comparator takes the place of transistors and measures the relative resistance of the LDR sensors. If there is a dark line on a light floor, when the left LDRs sense dark, they will turn off the left motor, causing the robot to turn left. The same goes for the sensors on the right side. Does this make sense?
Der Strom

Hi i've already implemented the circuit you had sent. But it seems that it doesn't function well. Can I ask what is the specs of LED used, the position of LDR and LED is the LED in between the 2 ldr, and the differential height of sensor with respect to height. Thank you so much!

 

[DerStrom8]

Hi i've already implemented the circuit you had sent. But it seems that it doesn't function well. Can I ask what is the specs of LED used, the position of LDR and LED is the LED in between the 2 ldr, and the differential height of sensor with respect to height. Thank you so much!

The LEDs are only indicators of which motor is on at which time. They can be put on the top of the robot so that you can see them, but they can be eliminated if you wish. They are really only there for aesthetics. The circuit I actually used was a little different in the sense that it had a 10K trimmer potentiometer to balance the sensors, and the LEDs helped to show when they were balanced. You may be able to find a copy of this circuit somewhere on David Cook's website or contact him to ask for the schematic. I found his circuit to operate rather well.
Though you could eliminate the other LEDs, it would be a good idea to have bright white LEDs at the front between each set of sensors to act as a sort of "headlight." This would illuminate the floor better so that the sensors can "see" the line better. This, also, is in David Cook's design.
As for the LDR sensors, they are bent to face toward the ground, approximately 1/4 inch from the surface. This will allow the white LEDs to light up the floor enough to help the sensors sense the line.
I hope this answered your question!
Der Strom

 

[zharie]

The LEDs are only indicators of which motor is on at which time. They can be put on the top of the robot so that you can see them, but they can be eliminated if you wish. They are really only there for aesthetics. The circuit I actually used was a little different in the sense that it had a 10K trimmer potentiometer to balance the sensors, and the LEDs helped to show when they were balanced. You may be able to find a copy of this circuit somewhere on David Cook's website or contact him to ask for the schematic. I found his circuit to operate rather well.
Though you could eliminate the other LEDs, it would be a good idea to have bright white LEDs at the front between each set of sensors to act as a sort of "headlight." This would illuminate the floor better so that the sensors can "see" the line better. This, also, is in David Cook's design.
As for the LDR sensors, they are bent to face toward the ground, approximately 1/4 inch from the surface. This will allow the white LEDs to light up the floor enough to help the sensors sense the line.
I hope this answered your question!
Der Strom

how can I contact him for the schematic?

 

[DerStrom8]

how can I contact him for the schematic?

Sorry, zharie. I was just reading his contact page and found that he doesn't send free schematics. Instead, he recommends you buy the book, which is called "Robot Building for Beginners." If you can't find it in any bookstores, he suggests you try your local library or try getting it on an inter-library loan.
Der Strom

 

[zharie]

how can I contact him for the schematic?

Is this a black line follower or a white line follower?

 

[DerStrom8]

Is this a black line follower or a white line follower?

It depends on how you connect the drive transistors to the 393. In his book, David Cook explains how to connect a DPTT switch that allows the robot to follow a white line, a black line, or just stand still.
I would definitely recommend you look for his book.
Der Strom