Long range Ir proximity detection

Discussion in 'The Projects Forum' started by varuntejavarma, Jun 5, 2014.

  1. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
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    Hello,

    I have to design a low cost Ir proximity sensor for long range detection upto 1.5 metres. I have modulated my signal using pic mcu and used a tsop sensor at receiver side. But i could get only upto 10 cms range maximum. I have tried using high intensity Ir emitters but saw no improvement.
    I am a newbie in this field and have no idea on how to increase the detection range. Anyone kindly help me out to solve this problem. I dont want to give up. any kind of help is appreciated.


    Thanks
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The focus (dispersion angle) of your LED emitter and the focus angle of your detector (photodiode or photo resistor). Look for something under 15 degrees for emitter and more than 30 for detector.

    Also, the frequency is important, some phototransistors cannot pick up with good sensitivity above 15khz. Some work up to 100khz or so. A photodiode (reversed biased LEd emitter) works much better at high frequencies.
     
  3. ronv

    AAC Fanatic!

    Nov 12, 2008
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    What are you detecting?
     
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Something is VERY wrong there!

    I have modulated an IR LED at 38kHz with a PIC, and the sensor can pick it up after bouncing off walls metres away!

    Mayeb you are not pulsing the 38kHz? You have to send pulses, because if you send constant 38kHz the sensor will reduce its gain and give you weird problems. Pulsing the 38kHz at 1mS on, 1mS off is pretty standard and works fine.
     
  5. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
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    Really!! I was wondering if i could acheive a long detection range with 5v supply and normal led's and photodiodes.
    I have checked the output of 555 timer. it shows the freq 56 khz.
    it would be very helpfull if you could post your circuit diagram though which i could know my mistakes and correct them
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Photodiodes? :eek:

    No for long ranges you need to use a 3pin IR sensor device, which has inbuilt amp and gain control;

    [​IMG]

    Normally they are used for remote controls, so they can easily detect the IR pulses from across a room.

    You generally need two 555 timers, one to generate the 38kHz carrier and one to switch it on and off for 1mS intervals.

    That is because the gain control circuit in the IR sensor like to receive pulses.

    I have heard one brand is OK with receiving constant 38kHz carrier but sorry i don't know which one, you would have to do some googling.
    :)
     
  7. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
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    hey, sorry for late reply. was on a vacation.

    I have used a tsop56 sensor. I have tried using pwm from pic mcu for pulsing signals at 56khz. but was getting a detection range less than that of 555 timer. I dont know what is wrong. maybe i am missing some basic things. I have attached the circuit diagram with 555 timer. when using the mcu, the o/p from mcu goes to base terminal of transistor.

    It would be very helpfull if you could tell me the changes to be made to acheive a better range.

    I was hoping to give up the idea of ir and trying other ways. But you said you acheivead a good range. could you also tell me what range have you acheived with Ir sensors. so that i can still work on this project.

    Regards
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    TSOP4856, pin 1= output, pin 2 = ground, pin3 = Vcc, pin no as per your drawing. Emitter should be in 950 nm range. Data stream needs to broken into bursts and blank, need 2 555's.
    Thumbnail is old beam break ckt just to give ideas, pin nos different.
    I forgot the error; V1 pin 3 only goes to reset on V2, caps go to + 5V.
     
    Last edited: Jul 9, 2014
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I have not used the 56kHz type of sensor.

    Normally the 38kHz ones tolerate a couple of kHz frequency deviation with no issues. And their range is excellent, across the room no problem. You should get close to that range with a 150 ohm LED resistor and 5v PSU.

    You could try varying the carrier frequency and testing if it affects range.

    Like Bernard said (and I mentioned earlier) you need to modulate the carrier frequency by turning it on/off so the receiver doesn't reduce its gain right down.
     
  10. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
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    sorry, my mistake, i drew the Rx pins wrong. so, i wasnt sending burts of data all these time. But there is a formula for dutycycle while calculating frequency. what does that mean. Isn't it the on off period??

    But thanks for the circuit. could you please clarify some doubts regarding the ckt:
    1.which one of the two 555 timers is for freq and period setting because, I am getting different values other than 38khz and 1 khz when i calculate the frquencies of both the timers
    2.the pin 3 of v1 goes to pin 4 of v2. where should i connect c5 and c6
    3, the cap values are uf right?

    It would be very helpful if you could explain the imp points of the circuit and which values to change for 56 khz and what to keep in mind while designing
     
  11. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
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    A lot of other Ir sensors would be using 38khz . i thought that would interfere with my object. So, I used 56 khz. I thought that the freq doesnt matter as long as you get the right sensor for it. So, do you think the performance is better with 38 khz and why?? If so, I would buy tsop38 sensor
     
  12. Bernard

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    Aug 7, 2008
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    Look at the values of R2-R4, & C1-C3, which do you think is the higher freq., Did you guess V2. Calculations always forget tollerances, that is why we have pots, & can then sub with fixed values if desired. As said in post # 8, caps go to +5V. Caps in μF. I'm out of time till Monday.
     
  13. THE_RB

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    Feb 11, 2008
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    I can't say because i have not tested a 56kHz type and compared them.

    However it looks very likely that your poor range issues are because you are not modulating the IR carrier, so try the dual 555 circuit first and see how that goes. :)
     
  14. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
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    yes, i shall try the circuit with 2 timers first. but i am confused on how to calculte resistor values for second timer. for the carrier freq in first timer, I have used online calculator to get the cap and r2 value, then i used a pot for r1 and adjusted it using oscilloscope to get 56 khz. But how could i calculate the on off period in second timer. according to the data sheet, i have to send a min of 10 bursts of 56khz and a gap time of 4 times greater than burst length. Please clear my confusion on how to calculate the on off period and how to select the resistor and cap values

    Datasheet (5th page):
    http://www.vishay.com/docs/82459/tsop48.pdf
     
  15. THE_RB

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    Don't worry about that spec. I think it's for minimum burst time to set the gain or something?

    Commercial remote controls modulate the IR carrier with about 1mS ON, and 1mS or 2mS OFF.

    If you set the other 555 to astable at 500Hz, with roughly 50:50 duty cycle (or 40:60, whatever) that will make roughly 1mS On and 1mS OFF and it will work fine. It's not critical.

    Your online 555 calculator should help you with the parts values.
     
  16. Maxfooo

    New Member

    Aug 24, 2013
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    Hey,

    I have been working a little bit with photodetection and I thought I might add something.

    It would wise to start by reverse biasing your photodiode, if you haven't already. Stick Vcc to a resistor(~200k) in series with your photodiode, with the cathode facing the resistor, and anode to ground. This will increase your data photosensitivity because of the diode (PN/PIN and photoelectric effect) property of the photodiode.

    At the junction between the resistor and photodiode stick a series capacitor to the input of a trans-impedance amplifier, an op amp with a huge 1-10 Meg Ohm feedback resistor to maximize your first stage gain.

    You can take low noise amp precautions, but you don't need to for only 1.5 meter.

    Next, thinking with SNR in mind, narrow your bandwidth (using bandpass) to keep the power spectral density of the noise low for however much power you are putting into your operating bandwidth. For filter design go here:
    http://www.ti.com/lit/an/sloa093/sloa093.pdf

    Make sure your fabrication abilities are cautious, because faulty soldering and misplacement of parts can make you go mad.

    I apologize for the lack of images, but I hope this description helps.
     
  17. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Hi MAxfooo, I believe he is using an integrated 3-pin IR sensor now, that has all the electronics inside it (like amp and gain control etc).
     
  18. Maxfooo

    New Member

    Aug 24, 2013
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    Bernard likes this.
  19. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
    36
    1
    Thanx Maxfooo, but i would try building the receiver circuit once i get the desired detection range with tsop sensor.

    Meanwhile, I have tried the circuit with two timers. I have modulated the second timer with 220 us on time and 720 us off time by adjusting the res and cap values using oscilloscope. i got a modulated signal :) . But now, My output indicator LED is on irrespective to the obstacle. It only goes off if i remove the Ir led from the circuit. I have already used an insulation around the IR led and there are no major IR sources around me. I dont know what is wrong and if i am missing any basic rules
     
  20. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Now you are seeing the insane sensitivity of the IR receiver in action!

    Since these things are meant to see IR light from many meters away, they are VERY sensitive, you will need to reduce the IR energy from your LED.

    Try drastically reducing the current in your IR LED by using a larger value series resistor.
     
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