View Full Version : White Line

06-23-2006, 03:22 AM
Hi, im gonna share in robocon Egypt 06 , i wanna ask a question about white line tracking or following , we have used LDRs + Leds ( to inverter)::
LDR in series with 10K and Leds in series with an LED and the output of the LDR is put to the inverter .. this worked but in outside enviroment it doesnt work , we've tried to shield it nothing new :( ... we have only one week till the beginning of the contest , need your opinions please :( everything works except the sensor .

thanks alot

06-23-2006, 03:49 AM
use the ldr's o/p to feed a comparator .....

set the threshold of d comparator using a potentiometer...

wen u r using it in an environment, see wat r d voltage values u r getting wen the ldr is above d white line and wen not... set the reference{threshold} value in between these two extremes...

u ll get clear logic with it and this ll work anywhere...u ll just need to tune the potentiometer...

06-23-2006, 04:02 AM
the problem is we dont have time at the beginning of the contest to tune the pot at the contest's enviroment... :(

06-23-2006, 11:45 AM
then tats sher stupidity if they re not allowing u to tune ur sensors...

anyway... go for infrared led based line following..
they ll hopefully not need tunning every now and then...
but be sure tat there re no infrared sources nearby in d competition,...

06-23-2006, 11:55 AM
thats right...they should be giving some time to first tune your sensors....IR sensors work best only when there are no IR sources nearby. And with lots of people, machines and lights around ur machine, i dont think an IR sensor would work satisfactorily unless you get a good one that will cost a bit more....

the best solution that i would recommend is to completely enclose your sensor by covering it and light the enclosed space by a simple LED and then fine tune your sensor...That will solve your problem i guess...
Best of Luck

06-23-2006, 01:00 PM
You can try using inbuilt ADCs of your microcontroller (if they have it) and then program it in such a way that it takes the initial value as the reference and then looks for the fluctuations as per that value.

06-23-2006, 06:09 PM
thanks alot
what about pulsing the emitter and use TSOP ? but i dont know how to differentiate betweeen white and green in that circuit ? by using a pot i know but where to put it ?

about the ADC method unfortuantely we use 89C52 , this is a good method but you know there's no time , but i do know is this method will take little time in experimting and my do a good result from your experience tell me please .

i wanna check an infrared circuit and connected to 74HC14 what about it ?

thanks alot , i've put three methods im really confused of which to choose now :( .

06-24-2006, 12:20 PM
http://img91.imageshack.us/img91/802/ldrckt32ee.th.jpg (http://img91.imageshack.us/my.php?image=ldrckt32ee.jpg)

Connect 10Ufd capacitor to the PWR+ pin to ground in parallel with .1uFd ceramic cap.
Use A for whiteline=Lo :arrow: OP 1C= HI
A =Hi :arrow: OP 1C= Lo

Use B for Whiteline=Hi :arrow: OP6C= LO
B =LO :arrow: OP 1C= HI

1. Use LED holders for both LED and LDR. Use Ultrabright White or Blue LED for better performance.
2. Arrange LED/LDR pairs at an angle so that the LED light reflects up into the LDR (say 30degrees. Put the LDR on the outer and the LED on the inside from the edge. This way the LDR is pointing inwards so that external light reflections dont reach it.
3. Adjust 100K preset/Potentiometer carefully for consistant triggering between Black and White.

4. Once adjusted, no further adjustment is necessary.

* Use a multi-turn pot, if necessary.
** This circuit is blind to all external light sources.

06-24-2006, 12:27 PM
Thanks alot, gonna Try it :D
but i need output 1 or 0 .. i mean need a A/D compartor ..etc ??

06-24-2006, 01:32 PM
oh docel....
u really narrowed it down to giving d ckts itself...
i thought u were against giving it????
u wantd guys to work dem out demself... right???

06-24-2006, 03:04 PM

The thing works both as analog as well as TTL level. The threshold of switching voltage is decided by the potential divider formed between Pot and LDR. If you assume 2Mohms for the Ldr in the dark and a few 100 ohms at full bright light, you can see that it achioeves trigger voltage at some light condition, decided by the POT resistance. This can be anywhere between .65 volts to 4.8v.

Put a 4.7volt zener , reverse biased between the Ldr-pot junction to the input pin. Then, the bias voltage for the Transistor/Ic input will be provided by the zener as it conducts.

I have made many LFRs with these: they work without problems.

# Can try a photodiode/phototransistor too.

Addy, I never said / is against giving circuits :lol: Just too lazy !!
Besides, this guy ahmedragia sultan is in a great terrible hurry and, may be I want him to win! Egypt is not across the road, is it??
Soooo.... :oops:

Actually this was supposed to be a PM 8O

06-24-2006, 10:47 PM
Actually this was supposed to be a PM Shocked

tat was a gud one!!!!!!!!! :D

# Can try a photodiode/phototransistor too
this ll work better than a tsop receiver...
so ahmed... go for a normal tx rx or a photodiode....

get up and get ur hand dirty now...