Proximity sensor

Discussion in 'General Electronics Chat' started by varuntejavarma, Jul 9, 2014.

  1. varuntejavarma

    Thread Starter Member

    Apr 16, 2014

    I want to build a Low cost proximity sensor for an automatic sense and spray device and i have choosen IR reflective property for this application. I have modulated the signal at 38khz frq and used a tsop38 sensor at detector side. But, I could acheive only a range of 10 cms. I have also tried using high intensity IR led's. I have tried different means but I could not acheive a long range with IR sensor.

    1. In general, I want to know, what is the maximum range of detection possible using a low cost IR sensor with 5v supply??

    In the mean time i have bought this product and opened the circuit.–-round-two/#comments

    It consists of only one diode. but i dont know which type of sensor it is. It cannot be PIR sensor. I think it triggers output with the change of light falling on it. It works very well upto 1.5 metre. The yellow led is just to indicate the status of the freshner. it blinks to show that the freshner is ready to detect any movement. if its stable it means the freshner is in sleep mode after completing a spray.
    The actual detection is done by the large diode. It works on passive detection. so there is no transmitter in the circuit. And it is not even pir sensor.
    my observation:
    when an obstacle is in front of the sensor, it doesnt trigger the output. it triggers only when the obstacle moves away. by this i think it works on movement of shadows. maybe it takes in the surrounding light as default and when there is a obstacle movement there would be change of light and the output is triggered. This is what i am thinking. I am not sure. Is there any possibility for a diode to work in that way. If yes, which type of diode is used and how does it work.

    How to find out which type of sensor is used in this circuit.
    how does this sensor work and what is its principle.

    It would be very helpfull if anyone could assist me in this project. It is my first project in electronics and i am tring the method of learning by doing and got no help around me

  2. Sensacell

    Senior Member

    Jun 19, 2012
    If you are using an IR remote receiver module and modulating the source at the required frequency, the range should be very long, 10's of meters at the least.

    Note that most IR receiver units are designed to receive pulses of modulated IR, a continuous signal is not what they like.

    Look at the specs for IR data transmission, the data is transmitted as short bursts of modulated IR, with idle time in between.

    Try pulsing the modulated (38 khz) beam on and off at 500 Hz., this will make the receiver's internal AGC work correctly.
    Last edited: Jul 9, 2014
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    the tens of cm's might not be possible for proximity detection, a tv remote is direct reception, a prox detector would be reflection, and depend on the reflectivity of what ever you were sensing.
  4. varuntejavarma

    Thread Starter Member

    Apr 16, 2014
    Exactly alfacliff. its a reflective Ir sensor not a direct reception. I have selected the res, cap values so as to modulate the transmitter at 56khz and did not do anything for the period. as it is in astable mode i assumed that the signals are switched on off on off with 50% dutycycle, but i have read in forums that i have to use 2 555 timers, one for frequency and other for period setting. so, could anyone tell me what to do and what should i modify in my circuit. a circuit diagram with some explanation would be very helpfull :)
  5. shakilabanu


    Jul 8, 2014
    1. your frequency should be 38Khz if you are using one of the standard TSOP modules.
    2. You will need a second timer or similar circuit, because the TSOP doesn't work with continuous signals.
    3. Have you considered one of the reflective optical proximity switches? There are some relatively cheep one that will cost about 500Rs or 10USD, that can work with ranges of even a meter.
  6. bertus


    Apr 5, 2008

    I have changed the size and colors of your picture for better readability: