About I.R. sensors.......

[RITESH29]

Hello Everyone,

I was just testing SOR IR circuit .....
I was just confused that above it was R2 20kohm Pot and at below R2 = 220 Kohms (calculate as above, or use Pot for white line following) so, is that any mistake ??
http://www.societyofrobots.com/schematics_infraredemitdet.shtml

and is there any cathode and anode of photo diode also if yes how to know?

[Cristi_Neagu]

If you would have looked above, you would have noticed this:

Or use a 20kohm Pot here in series with a 100ohm resistor for white line following calibration.

You either use a resistor, or, if the one resistor doesn't work properly, you could use a pot to calibrate the line follower.

[RITESH29]

I think you don't get me any way...
In above it is 20K then R2 changes too 220k

[Soeren]

Hi,

I think you don't get me any way...
In above it is 20K then R2 changes too 220k

You're mentioning R2 values for two different circuits.

[RITESH29]

ohhh.... It was may mistake.
Anyway I want to add some more doubt:-
1.) I am little confused how to find cathode and anode of Photo diode as it is black(opaque) from out.
2.) As per schematic value of all resistance is given, whenever i use pott. meter they never set to accurate and changes every time. so I want to have five sensors in BOT can i do multiplex with resistance to reduce the numbers of resistance.

[Soeren]

Hi,

Anyway I want to add some more doubt:-
1.) I am little confused how to find cathode and anode of Photo diode as it is black(opaque) from out.

You need photo transistors (PT), not photo diodes (PD), but perhaps it is PT that you have(?)

Some PT's have 3 pins (base, emitter and collector)and look exactly like a common transistor, only with a window (whether "black" to the naked eye or water clear), while others have only two pins (collector and emitter).

The incoming light goes to the base in both configurations and the PT's with the base brought out can be used to bias the PT to speed it up a little or a lot (while lowering its sensitivity proportionally).

Since I don't know which device you have (they come in many shapes), I can only give general advice...
Connect it up with like in the drawing in series with anything between 22k and 220k and measure the voltage over R2. Now cover the PT and the voltage should fall, then let light shine on it again and the voltage should rise - if it don't, reverse the pin connections.

The exact voltage change (light/dark) depends on the value of the resistor as well as your specific device, but anything from 1V upwards is proof it works.

If you cannot get at least 1V of change (no matter the way you connect it), it's probably a PD instead and that won't work in this simple circuit.

A datasheet will tell the connections as well (and have a lot more useful content). Always find datasheets on the components that you use - only way to know all the details.

2.) As per schematic value of all resistance is given, whenever i use pott. meter they never set to accurate and changes every time. so I want to have five sensors in BOT can i do multiplex with resistance to reduce the numbers of resistance.

Not sure I understand what you mean?
If light changes, so does the resistance value needed for a given output, but I don't think that's what you think of.

Do you want to have five sensors just to make up for the varying light, or do you want to 5 sensors and want to save 4 resistors by using more I/O pins?

Or is it just to save trimming potentiometers?
If so, take a look at this circuit, which is a 4 sensor circuit. It can be extended easily, but since op-amps comes in either singles, duals or quads, it made sense making a 4 sensor module, but in principle, any number is possible.

If you meant something else, please try to rephrase it

[RITESH29]

Hi,

I am using this as show in images....

Some PT's have 3 pins (base, emitter and collector)and look exactly like a common transistor, only with a window (whether "black" to the naked eye or water clear)

In three terminal the surface are is big so, i think it will pick some stray Infrared rays also,right?

or do you want to 5 sensors and want to save 4 resistors by using more I/O pins?

Yes...

The circuit you are telling  is totally diff. is there anyy way to find Resistance values?

[Soeren]

Hi,

In three terminal the surface are is big so, i think it will pick some stray Infrared rays also,right?

That's not determined by the area. A larger area just means it's more sensitive (and more sensitive to noise, but that's not an issue in this circuit).

I think you're really thinking of angle of incident light, rather than surface area and the angle has nothing to do with the number of pins.

The devices you have, do they resemble 3mm LED's, only black?

or do you want to 5 sensors and want to save 4 resistors by using more I/O pins?

Yes...

It could be done, but you'd need an analog multiplexer like 4051 and while you'd save 4 resistors, it would be more expensive and take up more PCB space.

The circuit you are telling  is totally diff. is there anyy way to find Resistance values?

The best way to find the resistance values is looking at the schematic - sort of like Find Waldo actually, just easier

The main difference from the other schematic is, that this circuit uses the op-amps like comparators, rather than as gain-blocks.

Each "op-amp-comparator" has got hysteresis by the 4.7 MOhm resistors, to avoid oscillation around the shifting point and they all share the same reference voltage from the wiper of VR1. This means that the photo transistors needs to be the exact same type and preferably from the same production batch (which they'll usually be if you buy a sealed bag of eg. 10 devices.)
The outputs are high/"1" when they see light.


If you want to make it as cheap as possible, just go with the first circuit on the page you referred to, the one without op-amps. The outputs can go directly to the I/O pins of a controller.

You just need to make one circuit, to find the best resistor value. Use a potentiometer or a trimmer to dial it in, then de-solder it without disturbing the position of the wiper and measure its value. Finally install resistors with the same value as you measured.

[RITESH29]

Hi again,

The devices you have, do they resemble 3mm LED's, only black?

Sorry i don't get u?

Each "op-amp-comparator" has got hysteresis by the 4.7 MOhm resistors, to avoid oscillation around the shifting point and they all share the same reference voltage from the wiper of VR1.

Can you explain me more about hysteresis in comparator, how??
that mean using gain block will not have hysteresis, right??

If you want to make it as cheap as possible, just go with the first circuit on the page you referred to, the one without op-amps. The outputs can go directly to the I/O pins of a controller.

No way i don't want to losses quality of signal...!!

ou just need to make one circuit, to find the best resistor value. Use a potentiometer or a trimmer to dial it in, then de-solder it without disturbing the position of the wiper and measure its value. Finally install resistors with the same value as you measured.

OK, I was just using that second gain block op-amp circuit in SOR the value of R2 was given as 200K but i don't find that efficient as compare to 20-30K .......
so, i think 20K pot. meter is best.

Finally install resistors with the same value as you measured.
But in some cases like outdoor using line follower will causes problem in its sensitivity, then how to change the reff. voltage..?

[Soeren]

Hi,

The devices you have, do they resemble 3mm LED's, only black?

Sorry i don't get u?

Never mind, I took a look at your blurry photos.
Do you know the name of the PT's and do you have a link to the datasheet?

Can you explain me more about hysteresis in comparator, how??
that mean using gain block will not have hysteresis, right??

Sorry, this is not the place for complete tutorials. Google the subject, there's plenty of tutorials on both op-amps and comparators on the web.

If you want to make it as cheap as possible, just go with the first circuit on the page you referred to, the one without op-amps. The outputs can go directly to the I/O pins of a controller.

No way i don't want to losses quality of signal...!!

What makes you think that you'd loose quality in that circuit over the other?

OK, I was just using that second gain block op-amp circuit in SOR the value of R2 was given as 200K but i don't find that efficient as compare to 20-30K .......
so, i think 20K pot. meter is best.

Electronics is not a guessing game. The resistance needs to be tailored to the effective resistance of the PT (under the various conditions it will operate) and the threshold value of the op-amp.

But in some cases like outdoor using line follower will causes problem in its sensitivity, then how to change the reff. voltage..?

There's plenty of ways to do that, but you need to understand the circuit and the components first and building the basic circuit will be a step in that direction.

Measure the needed resistance in all possible environments, outdoor in strong sun light, indoor in semi darkness or whatever. Then use a resistor a little lower in value than the minimum resistance needed and make up for the rest with a potentiometer in series.

It's possible to make automatically self adjusting circuits as well, but you need to start with circuits that you have a decent chance of understanding - and after a while, you'll be able to improve the circuits.

[RITESH29]

Hi again,

Do you know the name of the PT's and do you have a link to the datasheet?

I think its local Photo transistor....no data sheet provided.
and how to differ between photo diode and photo transistor?

Measure the needed resistance in all possible environments, outdoor in strong sun light,

I have measure the resistance in sunlight it was very less (negligible), can i use freq. modulation then filter it ..?
as we do this in Television remote control???

[Soeren]

Hi,

I think its local Photo transistor....no data sheet provided.
and how to differ between photo diode and photo transistor?

Since you can measure a large difference with a DMM, it's a transistor.

I have measure the resistance in sunlight it was very less (negligible),

"very less (negligible)" doesn't really tell me that much, as I have no idea of your frame of reference. I'd guess that anything from 10mOhm to a few hundred Ohm, perhaps a few kOhm might be considered a small value compared to the dark value, but you need exact numbers to complete the circuit.
Whenever you make measurements, take notes - they will come in handy when you need them but cannot make them, like measuring sun light at night (only works in two very cold areas ).

Since you need this for a line follower, you need to make the measurements like the sensors will be used, which is close to the ground and pointing down. Don't point the PT's into the sun, that wont give you a realistic result.
A shade can be made to shade the sensors, if the sun is still too bright when measured correctly.

can i use freq. modulation then filter it ..?
as we do this in Television remote control???

Yes, when you have learned to use them. For now, just build a single version of the simplest (i.e. non op-amp) circuit and mount it in a way that will give you realistic data. Then experiment and take notes along the way.
IOW, don't dream up more ways to solve a problem that you haven't verified the existence of yet - build the plain one and see if there is any issues that needs attention, you're just wasting time as it is.

[RITESH29]

Hi again,

I am really suck with this circuit, i don't understand this simple circuit is creating so much problem with IR as there is no datasheet for Photo diode I can't surely identifies the -ve and +ve terminal ( cathode and anode) + The value of R2 as i am using 50K pot. meter varying it is also not changing so much reference voltage to op-amp .....

any hint or suggestion that any one wants to give me for this problem will be appreciated..!!

[Soeren]

Hi,

I am really suck with this circuit,

Then compensate by listening

i don't understand this simple circuit is creating so much problem with IR as there is no datasheet for Photo diode I can't surely identifies the -ve and +ve terminal ( cathode and anode) + The value of R2 as i am using 50K pot. meter varying it is also not changing so much reference voltage to op-amp .....

Don't blame the missing datasheet. Identifying is simple - if it doesn't work, it's the other way around.

Do not use a potentiometer without a series resistor of a least 2..5kOhm. If you do and you then turn it fully to one side, you have close to 0 Ohm and bright light may then make the PT self destruct.
Perhaps you already did and then you probably need a new PT.

any hint or suggestion that any one wants to give me for this problem will be appreciated..!!

OK, but if you don't follow this, I'll stand down.
Build this basic circuit:

With the values:
V_cc = 5V
R1 = 220 Ohm
R2 = 100 kOhm

No potentiometers, just the above mentioned resistors (and the LED and the PT of course)!
Then measure the voltage at V_out (referenced from GND) under 3 different lightning conditions; Outdoor in sunshine, indoor in well lit room and finally in a semi-dark room. Remember to position the PT as it will be used on a 'bot.

Note each voltage reading and post the numbers with the condition under which it was taken (dark, light or inbeteen), then I can calculate the approximate value needed for R2 to get the output voltage you need.

Mind you, that if you do not produce these number, I'll consider you out of reach, as this really is a 2 posts max. problem.

[RITESH29]

Remember to position the PT as it will be used on a 'bot.

Sorry, i didn't get you..!!

[newInRobotics]

Remember to position the PT as it will be used on a 'bot.

Sorry, i didn't get you..!!

Put photo-transistor to where it has to be on the robot and then take measurements Soeren asked You for.

[RITESH29]

Hi again,

Put photo-transistor to where it has to be on the robot and then take measurements Soeren asked You for.

OK, i am just testing it on Bread board for now..!!

my reading are:-----

a.  Dark condition 3.8V max 1V min
b.  Bright             .7V max  .21V min
c.  Normal           3.3V max .20V min

max mean black and white -> min.

[RITESH29]

I forget to add these value of Resistance used..!!

R2-> 28K(pot) + 4.7K ( series)
R1 with IR Tx -> 600Ohms

[newInRobotics]

It works 

[RITESH29]

It works 

No need to add op-amps??

[newInRobotics]

If R2 is well picked - then no need for op-amp. Just wait for Soeren to come back to You with calculations he promised

[RITESH29]

Help needed......

[newInRobotics]

It would help if You wrote what help exactly You need. Or are we supposed to guess? 

[RITESH29]

I want to add gain block op-amps....
and why we use these op-amp why not this voltage divider circuit for IR sensors??

[newInRobotics]

I'm not sure I understand what You ask.

If You want to add op-amp to amplify the signal from IR circuit, why do You ask what op-amps are used for?

[RITESH29]

I was just asking as we have the voltage divider was giving good result....that mean using op-amp will give more result.
So, I was just confuse many time that what point to keep in mind while calculating the resistance..

[Soeren]

Hi,

OK, i am just testing it on Bread board for now..!!

my reading are:-----

a.  Dark condition 3.8V max 1V min
b.  Bright             .7V max  .21V min
c.  Normal           3.3V max .20V min

max mean black and white -> min.

I forget to add these value of Resistance used..!!

R2-> 28K(pot) + 4.7K ( series)
R1 with IR Tx -> 600Ohms

Next time, just use the "Modify" link to add it into the other post.

Even if on breadboard, you can take the entire breadboard and hold it upside down to imitate the intended use.

It's amazing how you, in a simple circuit with 2 resistors, can get 4 things wrong!

I'll just repeat it here...

Build this basic circuit:

With the values:
V_cc = 5V
R1 = 220 Ohm
R2 = 100 kOhm

No potentiometers, just the above mentioned resistors (and the LED and the PT of course)!
[...]
Remember to position the PT as it will be used on a 'bot.

Apart from that, where did you get a 600 Ohm resistor? There's no 600 Ohm resistors in the standard ranges.

If you want the circuit done and working, stop acting like a 9-year old that had way too much sugar and pay attention.
Forget about hooking up an op-amp, if you cannot even make this simple circuit work, an op-amp will just complicate matters - a lot.

You also need to understand how each component work, so keep things simple and you may have a chance of getting it together (although I'm starting to have serious doubts).

Try once more and do it as directed - including turning the breadboard (or at least the LED and PT) upside down. Don't let the sun shine into the PT, not even from the back - use black tape on the sides and the wire end if needed.

And please stop writing "Help needed......" posts - we already know that and such post are just annoying.

[RITESH29]

Hi again,

Apart from that, where did you get a 600 Ohm resistor? There's no 600 Ohm resistors in the standard ranges.

It was ~~600ohms

OK, i will try once more time using 100K and 220ohms...

thanks

[RITESH29]

Hi again,

I was waiting for clear cloud as there was raining regular.

So, today the climate was better than previous.

1.  in room medium white -> 0.12V black-> 0.16V
2.  in room bright    "            0.14V "           0.18V
3.  outside not so bright         0.13V             0.17V

[Soeren]

Hi,

1.  in room medium white -> 0.12V black-> 0.16V
2.  in room bright    "            0.14V "           0.18V
3.  outside not so bright         0.13V             0.17V

Looks like you have more light indoor than out in the sun.
I assume this is using 5.0V and a 100k resistor? (Always mention your measuring conditions to avoid mistakes).

If you had adjusted your voltmeter from the 20V range to the 2V range, the numbers would have been more reliable with better resolution - always adjust to the lowest range that will show what you measure without over-ranging.

Now change the 100k resistor to a 10k resistor and repeat the measurements in the correct voltmeter range, and confirm the component values and conditions. Then we'll see a more clear picture of the PT's range of equivalent resistance.

If you have overcast sky, just do the indoors measurements for now.