infrared IR motion detector circuit - Accurate Proximity Detector Circuit

Accurate Proximity Detector Circuit

The post explains an accurate infrared (IR) based motion detector circuit which incorporates the IC LM567 for ensuring reliable and foolproof operations. The circuit also works as a obstacle or a proximity detector circuit.

The Circuit Concept

I found this design on the net while searching for an accurate and reliable yet cheap proximity sensor circuit.

The circuit may be understood with the help of the following description:

Referring to the below shown infrared (IR) motion detector circuit, we see  the design consisting of two main stages, one involving the IC LM567 while the other with the IC555.

Basically the IC LM567 becomes the heart of the circuit which solely performs the functions of the generating/transmitting the IR frequency and also detecting the same.

Moreover the IC has an internal phase locked loop circuitry which makes it highly reliable with frequency detecting  circuit applications.

It means once it reads and latches to a given frequency, its detection feature gets locked to that frequency and therefore any other stray disturbance no matter how strong it may be doesn't influence or rattle its functioning.

Circuit Description

An internal oscillator frequency determined by R3, C2 feeds the IR diode D274 via a current controlled stage consisting T1, R2. This frequency decides the center frequency of the chip.

With the above conditions the IC gets set and centered at the above frequency generating a constant high at its output pin#8.

Input pin#3 of the IC waits to receive a frequency which may be exactly equal to the above "centered" frequency of the IC.

The IR receiver or the sensor connected across pin#3 of the IC is positioned exactly for this purpose.

As soon the IR beam from the LD274 finds an obstacle, its beam gets reflected and falls on the appropriately positioned detector diode BP104.

The IR frequency from the LD274 now passes to the input pin#3 of the IC, since this frequency will be exactly same to the set center frequency of the IC, the IC recognizes this and instantly switches its output from high to LOW.

The above low trigger at pin#2 of the IC 555 which is configured as a monostable  in turn switches its output high, causing the connected alarm to blow.

The above condition persists for so long as the interruption from of the IR sensor/ detector stays and allows the beams to get reflected. With the inclusion of R9 and C5, the output of IC555 exhibits a certain delay off condition for the connected buzzer even after the motion or the obstacle moves away.

For adjusting the delay-off effect, R9 and C5 may be tweaked as per preference.

The above explained circuit may also be used as a  proximity detector circuit and obstacle detector circuit.

Circuit Schematic


LM567 - Accurate Proximity Detector Circuit



42 thoughts on “Accurate Proximity Detector Circuit

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. dear Swagatam Majumdar,
    greetings! i've been reading some of your blogs. it's really really great! i don't know what to say, as i read your generous. anyway i hope you can help me with these noob questions. i really like to learn electronics, building circuit board with your help. sorry for posting it here not in the right section.

    i use 1 ups(220v) 400watts 12volts battery. i placed 3 parallel arrangement 12 volts battery instead of one. i would like to charge the 3 parallel 12v battery without damaging the ups or should i place switches every terminals and turn it off when i'm going to charge 2 batteries. or it's better to place diod or something.

    i've uploaded what i did. kindly see the link below.


    • The diode curent will depend on charging current, or the AH of the battery under charge. The diode rating should be twice of that.

      Yes your connections are correct, the output common cathode points of the diodes will go to the inverter positive.

    • I've test the charger's current there's 12v slow charging, 13v for medium and fast 14v. maybe i'll used the 13v for charging all three of them(car battery i think 3pc of 2sm battery).
      i haven't reached the diodes lecture part yet. sorry bout that. please enlighten me more. thanks again.

  3. thank you very much. will get 3pc. for 3 battery of 6A4 diodes and 1pc mosfets P-channel 50 and 470 ohms. finally my first time of assembling with diodes and mosfets.

    I've been reading your timer circuit. but can't find an easy diagram for noob (me) is it possible to build a small and easy circuit board for a dc fan 12v. power on time 5 to 10 mins, then off within 20 to 30 mins. thank you very much engineer Majumdar!

  4. oh…ok i'll get the diodes.. many many thanks!
    yes probably more time on learning electronics first before i can build Programmable Timer Circuit. thanks again. will let you know a few more weeks if i have built your Programmable Timer Circuit. thanks again for not giving up on me, take care Swagatam!

    • Dear Andrea,

      I think it can be tried.

      you can replace the transmitter diode LD274 with the IR diode of the module and remove T2/D2 and replace them with the modules phototransistor

  5. Hi sir,

    what is range for sensing? how these LD274 are placed?
    I want to detect movement in restricted area for big space like CCTV camera when movement is happen camera capture visual like this i want a circuit for movement capture & responce alarm.
    What is diffrence between Phototransistor Photo diode & LDR?

    • Hi Ashok,
      the range is about 5 meters approximately.

      both sensors are pointed outwards (in parallel) for throwing and capturing reflected beams when an object is detected in the range .

      function of photodiode and photo transistor are basically the same and these will produce a tiny electrical signal in response to light triggers.

      An LDR is a light dependent resistance and will change its resistance value in response to light intensities.

  6. hello sir, how can i simulate this circuit? my professor requires me to simulate the circuit first before prototyping it to check whether the circuit functions well, i have tried to simulate it in Multisim, but i dont know if its really working with the output that i got, thank you sir! hope you can help me.

  7. Dear Swagatam Majumdar,
    What is the approximate range of this proximity sensor? Anything between 10 cm to 80 cm will do, since I'm going to build a parking sensor for a vehicle.

    • Dear Pinaki, its range is equivalent to our TV remote control range, may be around 5 meters or a little more.

      the range can be decreased as required by appropriately adjusting the angle of the Tx/Rx sensor devices…

  8. Dear Mr. Majumdar,
    1) I want an output port to monitor the voltage level with micro-controllers. Voltage level should be readable with multi-meters and MCU's ADC.
    2) A preset resistor is required to adjust the distance precisely.
    3) An on board LED to indicate obstacles at defined range is also required.
    Please suggest me accordingly.

  9. Can I get an analog voltage reading from somewhere else, so that I can at least measure the voltage with a multi-meter?
    How can I adjust the distance? I also need an on board LED for obstacle indication. I'm looking forward. So, Please..

    • at what points do you want to measure the voltages?

      the distance cannot be altered with a resistor, you'll need to change the angle of the sensors in order to vary the range of the sensors.

      LED can be added across pin#8 and the positive line with a series 1K resistor…this will light up whenever an obstacle is detected

    • I just want to measure the voltage just because I want to calculate the distance of the object in terms of voltage.
      Our MCUs those who have an on-board Analog to Digital Converter (ADC), act like a volt-meter, e.g. AVR. If a data is expressed in terms of voltage it can be used with an MCU with its on-board ADC or a dedicated ADC IC. I will write the code for this. It would take a while but the job will be done. But the question is to measure it somehow.
      Can I measure the voltage when the distance of the obstacle varies?

      If there was a way to vary the distance from the circuit it would have been be so useful. I am going to build a car parking sensor so I need the sensor to be adjusted at 2 feet only.

      If I could light up 4 LEDs at different distances, at least the issue would have been fixed by now. Waiting to hear from you.

    • OK, but here the distance is no way related to voltage levels anywhere in the circuit…the distance is a just matter of changing the sensor angles…for example if the angle is made acute that would result in a shorter range detection, while if the angle is widened that would allow obstacles to be detected from longer distances.

    • The above circuit is based on IR principle identical to our TV remote controls…these remotes as we know have the ability to switch ON the TV even when it's pointed to an opposite wall…so the concept can be pretty sensitive and long ranged.

      I could not publish your recent comments because of the external links in it….

  10. Dear Swagatam

    I am hobbyist in electronics for last so many years and 48 years old person.
    I have made Simple Proximity Detector Circuit from an other circuit and designed the PCB my self. Actually I need a long range IR prox. Detector for my washroom, car, main gate etc. I am already using it out side my washroom. When I made this circuit as proto type on bread board it was giving full range like 1m to 1.5m. But made on pcb it is not giving proper range. I operate it with 1.5m capacitor dc power supply as well as on 150ma transformer. but the transformer supply is giving little bit more rang but not full range. I can send you JPG and Coreldraw CDR files. Pls Suggest me about the PCB design errors as well as diagram.
    I need your help.

    Thanks & Regards


    • Dear Rakesh, It would be difficult to point out the fault just by referring to the PCB, it won't be a foolproof approach….so I think you may have to redesign the PCB or compare the present design with the schematic stagewise for locating the exact possible fault.

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