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shyam4uall
09-14-2008, 07:35 PM
Please help me....i can't get those bursts ??? I can generate 33Khz frequency through 555 but its continuous one ,how to make those with bursts ??

I am not using any PIC.I have heard that the bursts can be produced through another 555 but how in which mode they should operate and what frequency it should generate ?

I am using TSOP 1333 for IR detection.

shobhitkukreti
09-15-2008, 12:36 PM
use and gate with another 555

shyam4uall
09-15-2008, 05:48 PM
Thanks shobhitkukreti for your reply...but can you..explain it a little bit more.

shobhitkukreti
09-16-2008, 09:37 PM
Please read this http://www.roboticsindia.com/modules.php?name=Forums&file=viewtopic&p=8548&highlight=#8548

Also take a 2 input and gate and couple both inputs of the and Gate with outputs of different 555. One will supply the 33Khz frequency signal, and other will provide the bursts. Please refer to the datasheet to check out the burst length. Since the other 555 will be at lower frequency than the main one which generates the 33khz freq, it will allow the 33khz frequency to pass through for some time depending on the burst length.

shyam4uall
09-16-2008, 10:34 PM
I tried a lot but its not working...I have used the circuit in the below link

http://home.cogeco.ca/~rpaisley4/IrProximity.html

the basic one with 3Hz pulse (556A) and 33Khz for 556B.

but its not working....and one thing..when i align the IR LED in the direction of TSOP then there is a slight voltage variation but when used for objects i.e reflection of IR is needed the TSOP is not responding.

What should I do ?? Is there any other way out for obstacle detection ?

vikas
09-16-2008, 11:24 PM
Use tsop 1738 , first time heard using anyone 1333.

Generate a continues 38khz from 555.

And use it for obstacle detection , no need for bursts ... it works just fine.

Not exactly this ... but this might help :)

http://www.electronicsforu.com/electronicsforu/lab/ad.asp?url=/EFYLinux/circuit/January2006/CI-Jan06-02.pdf&title=IR%20Burglar%20Deterrent

shyam4uall
09-16-2008, 11:54 PM
Thanks...Vikas for your reply..

I have worked on TSOP 1738 when i first designed the circuit and hopefully..it was detecting..a continuous 38 Khz signal but when I tried to make the circuit once again with the same TSOP 1738 ,it was not responding(or you can very small i m saying very very..small change was detected)

i don't know whether its sensitivity is decreased due to continuous 38 Khz when i experimented for the very first time.

vikas
09-17-2008, 01:57 AM
TSOP outputs a digital signal , there is no small or big . Just high or low.

Incase a carrier is detected it goes low.

Check ur circuit. Are ur emitters working fine , use a web cam to check ... and CRO to check if frequency is correct. Check if TSOP working ok , they easily go bad with incorrect connections etc.

There are few things that can be wrong , just check the circuit.

shyam4uall
09-17-2008, 11:02 AM
I have checked the frequency with CRO which is within the 38Khz bandwidth varying 37.XX to 38.XX so I think this part is ok.

As far as the TSOP is concerned....how to check whether its working or not.

The output goes low when it detects the IR for the very first time (when the IR is aligned in the direction of TSOP not any reflection stuffs..) and then the output remains high even if the IR is continuously aligned to the TSOP.

docel
09-19-2008, 05:07 AM
1. TSOPs dont respond to continuous 38khz signal. It will just output a momentary low and go back to high. This momentary low will occur with ordinary sunlight too.

2. The correct operation of the TSOP is output LOW. This is a pulsing low, depending upon the 'burst' frequency.

3. The TSOP is a very sensitive device. It will detect even low 38khz signals, from ALL directions, but the detection has maximum range from the built-in cylindrical "lens".

4. Do NOT connect LEDs directly to the output pin. This will gradually fry the TSOP. You need a buffer, either a TTL/CMOS inverter or a simple transistor to drive an LED.

Some Forums blatantly publish wrong information regarding the TSOP series. It is up to the user to decide if it is wrong or right, ofcourse. A through understanding of the Manufacturers datasheet is the right way to start.

shyam4uall
09-19-2008, 07:56 PM
thanks docel

i m trying both TSOP1738 and TSOP1333 whichever works but seems neither working for me.

After searching through forums i got some idea about how to create bursts.But the problem is that i am not so sure about the calculation part (frequency and all).

I have to use another 555 generating a frequency of 3.8 Khz (or it should be 3.8 Hz i dont know) and connecting its output to the trigger of another 555 which is generating 38 khz.

but confused whether the output of the first 555 (3.8Khz) should be inverted or directly connected to the trigger of the second 555 ??

but above shobhitkukreti have written that the output of the both 555 timer should be ORed ???

Confused .....guys please help me.

allbits
09-19-2008, 09:24 PM
As far as the TSOP is concerned....how to check whether its working or not.

.. Use a TV remote, fire it at the TSOP, and check the output to see if the TSOP is working.



.
The output goes low when it detects the IR for the very first time (when the IR is aligned in the direction of TSOP not any reflection stuffs..) and then the output remains high even if the IR is continuously aligned to the TSOP.

.. you need to turn the 38Khz on and off periodically, at a lower frequency. a 555 is held in reset when the reset pin is low. Wire two 555 in astable mode, one with 38 Khz and other with a lower frequency. connect the output of the lower frequency one to the reset of the other one. That will be enough.

By using a logic gate, you are unnecessarily adding an extra chip. Also, it should be an AND gate. (You dont want the IR to be ON most of the time..) I guess shobith meant an AND gate.

Also, many a times, TSOP will work with continuous signals. It has worked with me most of the times, but there were times it did not. The problem comes when you have all your PCB set up, working, and one fine morning , you replace your faulty TSOP just to see that the new one does not respond to continuous signals.

Yes, it works mostly, but its always better to trust the manufacturers data sheet, as doc said.

Good luck.

shobhitkukreti
09-20-2008, 04:06 PM
hey.. sorry.. and gate could be used, was thinking of something else then, i apologise, and you need to read the datahseet of 555 and understand it's working, it is not that tough,


assume : _ _ _ _ _ _ _ _ _ 38 khz freq, where _ is high o/p and empty space is o/p low

this is your low freq signal .____ _____ ______

Basically untill the low freq signal is high the 38khz signal will be received as output on your LED, however as soon as the low freq signal goes low, the 38khz signal will not be received at output.

That is how you will receive bursts of 38khz

shyam4uall
09-21-2008, 12:34 AM
Just one more question....regarding the timer and all....I have made one 555 timer to generate 3hz at 9% duty cycle to trigger another 555 timer generating the 38Khz at 52% duty cycle.

As u said that the TSOP will only give O or 1( Vcc) as output but I am not getting that instead the voltage at PIN 3 is continuously changing from around 2.8 V to 2.4-2.1 V at a very fast rate.

And also..the LED connected to PIN 3 of the TSOP is blinking even if the IR is covered from all side. Don't know why ??So can't find out whether the IR is getting reflected from any obstacle...or not bcoz even in the absence of obstacle it remains in that state i.e blinking (opposite to that of IR -active low).

Do I need to change the duty cycle of any 555 or its fine ??Do i need to increase the duty cycle of the lower frequency timer ??

shyam4uall
09-27-2008, 02:10 PM
hey.. sorry.. and gate could be used, was thinking of something else then, i apologise, and you need to read the datahseet of 555 and understand it's working, it is not that tough,


assume : _ _ _ _ _ _ _ _ _ 38 khz freq, where _ is high o/p and empty space is o/p low

this is your low freq signal .____ _____ ______

Basically untill the low freq signal is high the 38khz signal will be received as output on your LED, however as soon as the low freq signal goes low, the 38khz signal will not be received at output.

That is how you will receive bursts of 38khz

what should be the low frequency ? Will 380 Hz do the work or i need to lower the frequency ??

shobhitkukreti
10-02-2008, 11:36 AM
For reliable operation burst length> 10cycles/burst. So think about this way the ON Period of Lower frequency should allow at least 10 cycles of 33/38khz. It is just like switching the 33/38 khz frequency circuit ON/OFF very rapidly but lower than 38 khz to allow at least 10 cycles.
According to the circuit 3hz should also be fine, try 1.8khz or lower

shobhitkukreti
10-02-2008, 11:43 AM
The output of TSOP is average value which you are getting. read the post by docel, it is pulsing low and voltmeters are not good enough to catch that pulsing low that quickly