Ultrasonic Sensor Circuit

This Ultrasonic Sensor Circuit consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered the circuit’s fine balance is disturbed and the alarm is triggered. The ultrasonic circuit is very sensitive and can be adjusted to reset itself automatically or to stay triggered till it is reset manually after an alarm.

The ultra sonic transmitter is built around two NAND gates wired as inverters and they form a multivibrator the output of which drives the transducer. The trimmer P2 adjusts the output frequency of the transmitter and for greater efficiency it should be made the same as the frequency of resonance of the transducers in use. The ultrasonic receiver uses a transducer to receive the signals that are reflected back to it the output of which is amplified by the transistor TR3, and IC1 which is a 741 op-amp. The output of IC1 is taken to the non inverting input of IC2 the amplification factor of which is adjusted by means of P1.

Related Products: Flow Sensor Proximity Sensor

How the ultrasonic sensor works?

ultrasonic sensor picture

The ultra sonic circuit is adjusted in such a way as to stay in balance as long the same as the output frequency of the transmitter. If there is some movement in the area covered by the ultrasonic emission the signal that is reflected back to the receiver becomes distorted and the circuit is thrown out of balance. The circuit works from 9-12 VDC and can be used with batteries or a power supply.

Ultra Sonic Detector Construction

The board is made of a thin insulating material clad with a thin layer of conductive copper that is shaped in such a way as to form the necessary conductors between the various components of the circuit. The use of a properly designed printed circuit board is very desirable as it speeds construction up considerably and reduces the possibility of making errors. In order to solder a component correctly you should do the following:

  • Clean the component leads with a small piece of emery paper.
  • Bend them at the correct distance from the component’s body and insert the component in its place on the board.
  • You may find sometimes a component with heavier gauge leads than usual, that are too thick to enter in the holes of the p.c. board.
  • In this case use a mini drill to enlarge the holes slightly. Do not make the holes too large as this is going to make soldering difficult afterwards.
  • Take the hot iron and place its tip on the component lead while holding the end of the solder wire at the point where the lead emerges from the board. The iron tip must touch the lead slightly above the p.c. board.
  • When the solder starts to melt and flow wait till it covers evenly the area around the hole and the flux boils and gets out from underneath the solder. The whole operation should not take more than 5 seconds. Remove the iron and allow the solder to cool naturally without blowing on it or moving the component. If everything was done properly the surface of the joint must have a bright metallic finish and its edges should be smoothly ended on the component lead and the board track. If the solder looks dull, cracked,or has the shape of a blob then you have made a dry joint and you should remove the solder (with a pump, or a solder wick) and redo it.
  • Take care not to overheat the tracks as it is very easy to lift them from the board and break them.
  • When you are soldering a sensitive component it is good practice to hold the lead from the component side of the board with a pair of long-nose pliers to divert any heat that could possibly damage the component.
  • Make sure that you do not use more solder than it is necessary as you are running the risk of short-circuiting adjacent tracks on the board, especially if they are very close together.
  • When you finish your work cut off the excess of the component leads and clean the board thoroughly with a suitable solvent to remove all flux residues that may still remain on it.
  • There are quite a few components in the circuit and you should be careful to avoid mistakes that will be difficult to trace and repair afterwards. Solder first the pins and the IC sockets and then following if that is possible the parts list the resistors the trimmers and the capacitors paying particular attention to the correct orientation of the electrolytic.
  • Solder then the transistors and the diodes taking care not to overheat them during soldering. The transducers should be positioned in such a way as they do not affect each other directly because this will reduce the efficiency of the circuit. When you finish soldering, check your work to make sure that you have done everything properly, and then insert the IC’s in their sockets paying attention to their correct orientation and handling IC3 with great care as it is of the CMOS type and can be damaged quite easily by static discharges. Do not take it out of its aluminium foil wrapper till it is time to insert it in its socket, ground the board and your body to discharge static electricity and then insert the IC carefully in its socket. In the kit you will find a LED and a resistor of 560 — which will help you to make the necessary adjustments to the circuit. Connect the resistor in series with the LED and then connect them between point 9 of the circuit and the positive supply rail (point 1).

Connect the power supply across points 1 (+) and 2 (-) of the p.c. board and put P1 at roughly its middle position. Turn then P2 slowly till the LED lights when you move your fingers slightly in front of the transducers. If you have a frequency counter then you can make a much more accurate adjustment of the circuit. Connect the frequency counter across the transducer and adjust P2 till the frequency of the oscillator is exactly the same as the resonant frequency of the transducer. Adjust then P1 for maximum sensitivity. Connecting together pins 7 & 8 on the p.c. board will make the circuit to stay triggered till it is manually reset after an alarm. This can be very useful if you want to know that there was an attempt to enter in the place which are protected by the radar.

Source – read the rest of it.

Ultrasonic Sensor Components

ultrasonic radar components

UltraSonic Sensor Circuit Diagram

ultrasonic sensor circuit diagram

PBC Layout

ultrasonic detector pcb


Join the conversation!

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  • charly

    Hi Artois. First time I built this circuit on a copperboard (veroboard) and powered it with a pp3 9volts battery, it worked for a while and later stopped. I built another one using another set of transducers and same thing happened. I think that the transmitter transducer works still cos I can hear the tweet when I adjust P2. Pls what do you think I should do cos my time is running out. Thanks.

  • artois

    hi all
    c4 is between ic1 r2 end an tr3 coll

  • artois

    n1 n2 n3 n4 make up ic 3 look at. Schematic pin 3 and 5, and 6 are linked but not on the pcb. Pcb has a mistake they 3 5 6 should be linked and u will see it works

  • artois

    hi jim keith,i’m not an electonic spe i do this as a hobby an things to use. this unit does work as i have used to capture snakes, rats etc for relocation their r mistake if u read all the posts i have posted and build it u will c it does function feel free to email me if the webmaster will allow
    regards john

  • Matt

    Where is C4? Please someone help me.

    • Ludmil

      I mean C4 is between TR3 and IC1, connected bellow R2 and R17.

    • Ludmil

      C4 is a coupling capacitor between R2 and R17 value 2nF.

    • artois

      send me ur email an i will send u pic

    • Matt

      Trying this again since last time the post with my email got removed :S


    • Jim Keith

      C4 does not appear on the schematic –this is my take:

      C3 is wired as a phase compensation capacitor for OP amp IC1 –however, IC1 is listed as a 741 and a 741 has internal compensation and does not /cannot use an external capacitor. Most likely C4 was used as a compensation capacitor for IC2.

      The initial circuit design probably used the ancient LM709 OP amp that requires external compensation, and in the course of time was updated to the LM741, but the schematic was only partially updated.

      I have a problem with the circuit because IC2 is configured as an AC amplifier, but appears that it is supposed to detect a DC signal coming out of voltage doubler detector (D1 & D2)…and then AC coupled via C10 into IC2 non-inverting input that is DC fixed biased via R7 to the positive rail…cannot work…
      Looks all screwed up…that is my take.

    • Jim Keith

      It appears that artois has built it successfully –post your email and get his info.

      My take must be incorrect –first time that ever happened… 😉

    • Matt

      So this circuit doesn’t work at all? Or is there something that can be done to make it work? I guess i have to cancel my project if it’s all screwed up 🙁

  • darwin

    i need ur help guys!

  • darwin

    hi all, can i use this circuit in my electronic cane project?

  • Tabish Faheem

    Hi frnz.I am looking forward to make this project.Please let me know if i assemble it exactly the same way,will it work or is there any error in pcb.What is the max range???Please send me a prototype(clear image) of the assembled ckt on my id( reply promptly.
    Tabish Faheem

  • Costin

    Hello! What is the maximum distance of this circuit and what output has?

  • shalam

    Hi. We are a group of students from Temasek Polytechnic, Singapore. We are currently doing a project on ultrasonic tranducers to measure blood flow rate in a hemodialysis machine. This is done by placing a pair of transducer on the tube of the machine.

    First of all, since the diameter of the tube is about less than 1cm, we require the transducer to be around 1mm and we require more than 1 pair of transducer for accuracy.
    Secondly, we don’t know how to come up with the schematic to operate the tranducer.

    Our supervisor insist on using ultrasonic method with very small probe and also transceiver and receiver method(ie. One transmit on side, one receive on the other).

    Hence, we would like to know your opinion or suggestion on our project. thank you.

    pls do email me if there’s anything. thank you….