View Full Version : Ambient light reduction in line followers

11-24-2007, 08:13 AM
I guess this (ambient light reduction) topic was not discussed much in this forum (please correct me if i am wrong - )

The problem statement would be with visible light -

1) Ambient light effects on the sensors of a line follower
2) Ambient light effects on a look ahead sensor

even though ambient light reduction calls for modulation, I would like to have a discussion on the techniques used by members including methods to cover up the sensors, sensor placements etc, along with successful modulation with visible light.

11-24-2007, 11:00 AM
Good topic for discussion Allbits!
A lot of problems with failed projects is the little understood science of light and its behaviour [i]- in the Sensor's point of view[/i !!

Ambient light and its effects are also dependent on the Light source and the Sensor band-pass and beam-width

There should be a keen discussion on this!

11-25-2007, 12:22 AM
excellent topic... i have been facing this problem for my life, lets finish it once for all!

now i shall tell you what i used to achieve the task...

1.in my first line follower i had used ldr, now i needed to shield it from ambient light, so the sensor assembly was completely shielded with a black paper...the most natural idea...

2.but now there is some space left between the floor and the paper, and now imagine some light falling on the floor and getting inside the sensor assembly...so when i used to flash a torch ldr used to trigger...so i thought of new idea,
a vertical paper, and at the bottom side fold it for around 3-4cm parallel to the floor.And the paper,s lower side is colored black. Now when idiot light tries to get in it has to reflect from the floor, then from the black surface of the paper, and so multiple reflections. And the black surface makes the intensity of the light to go down almost to zero...we fooled light!! now when i flash torch, ldr does not trigger!

3.Using IR emitter receiver...put on the IR take the analog reading, put it off and take the reading, and consider the difference between these two readings as your actual reading...when we put off the emitter we get ambient light reading say 'ambient'...now when we put on the emitter. the intensities of IR and ambient light get added, so what we get is 'ambient+IR' now when we take the difference we get 'IR'!! so thats done.
Works OK for line sensors. Not good for distance measuring actually.And the villain are, sunlight, halogen light...

4.Modulated IR. Right now i am working on these. And i want heavy help from the experienced folks! as for the newbies...we transmit IR at a particular frequency say 40khz. Then at the reciever point we receive the IR.These IR is the sum of ambient IR (which is relatively of constant intensity, or changes with very less frequency) and our friend IR which is at 40khz. now we first amplify the signal. then we pass it through band pass filter, which allows only the contents which are at particular freauency and blocks other frequency signals. so naturally we let go our friends, 40khz and block stupid low frequency ir. so we get the signal which is at 40khz, and carries information of how far the obstacle is or of what color the floor is...

5.Filtering through coding. I have to work on this after i finish with filter circuit. here also i need help from seniors...[/quote]

11-25-2007, 08:36 AM
.......have you, at anytime, looked at the world through a pipe....... :?: :wink: :wink:

12-06-2007, 08:53 PM
And i did really wish there was a keen discussion on this..


Looks like there are few competitions which have to consider the ambient light!! and that there are very few who have plenty of free time (like me??
:roll: )

I was always bugged by ambient light, So often, I have avoided any sensors which uses visible light, except in the case of a line follower. Now, I have heard of people using modulation for ambient light elimination. I would like to know different aspects of this.

My question would be - Even if we use modulation, how do they solve issues like saturation?? as if the noise did override the modulated signal??

Or have anyone tried with double sensors- one for ambient light, and other for the reflected wave ?? and a subtraction??
( I am referring to problems in VISIBLE light, not the IR ones.. )

12-07-2007, 07:58 AM
Ya Allbits,
Differential Light Sensors....Wonder how many have tried it?? But if someone did try, he would have realised it really isn't necessary. By the time anyone reaches the multi sensor level, they'll KNOW the sensor behaviour thoroughly.

Shreek..! ( do you really need that loooong handle? :D:

Modulated IR:

I don't see the need for a Microprocessor at all.
:idea: I always propagate non-uC designs at all my Workshops.
One of our Logic design LFR is beating all uC driven LFRs at 2:1 timings, at complicated LFR tracks. 8 1st places till now... A lot of my students are competeing with these simple designs at Bangalore and its nice to see the competition: Logic Vs uC !!

This Forum is full of only uP designs. You can achieve good results only with some real "slick" software. Otherwise , the uC advantage is lost. There is no point in burdening the uC with unwanted processing of Analog signals and doing so is paid for with the price of Time.

:arrow: Now i suggest :
Try your hands on common Logic design with an Analog front-end.
Review methods of analog signal processing. The output can interface to a uC , or directly to a Motor driver.

:idea: We have some fantastic band-pass filter ICs around......all you need to do is FIND them!!

Let me know what all of you think and we can rediscover some excellent designs to beat the ambient !.

01-01-2008, 09:25 PM
We have some fantastic band-pass filter ICs around......all you need to do is FIND them!!

I only found MAX263-68 IC ... they needs to be programmed ? :?

Please put some more light on it ...
Do you know any other ...

01-02-2008, 02:51 AM
Hi Thirthankar,
MAX 26X is an overkill for this simple application!!!!!

All you need is a pre-settable active filter, for a not so narrow band-width. This is easily achieved with simple components.

There is , also, a simpler solution: just use a PLL.

Me? Well, I use an Audio Equaliser circuit......... :wink: :!: :!:

01-02-2008, 09:19 PM
Me? Well, I use an Audio Equaliser circuit.........

Bro you rock !! ..thats where the experience comes into play .....

01-06-2008, 01:06 AM
I guys had I been there I would have initially tried by covering the robot platform with a black paper skirt around the perephere.......If it failed I would have tried all other options .