A different type of remote control circuit employing ultrasonic signals is given here.

The transmitter part of the circuit is build around IC1(NE 555).The IC1 is wired as an astable multi vibrator operating at 40KHz.The output of IC1 is amplifier the complementary pair of transistors ( Q1 & Q2) and transmitted by the ultrasonic transmitter K1.The push button switch S1 is used the activate the transmitter.

The receiver uses an ultrasonic sensor transducer (K2) to sense the ultrasonic signals. When an ultrasonic signal is falling on the sensor, it produces a proportional voltage signal at its output. This weak signal is amplified by the two stage amplifier circuit comprising of transistors Q3 and Q4.The output of the amplifier is rectified by the diodes D3 & D4.The rectified signal is given to the inverting input of the opamp which is wired as a comparator. When ever there is an ultrasonic signal falling on the receiver, the output of the comparator activates the transistors Q5 & Q6 to drive the relay. In this way the load connected via the relay can be switched. The diode D5 is used as a free wheeling diode.

Circuit diagram with Parts list.




  • Assemble the the circuit on good quality boards.
  • The switch S1 can be a push button switch.
  • The ICs must be mounted on holders.
  • The transmitter can be powered from a 9V PP3 battery.
  • For low power applications the receiver can be also powered from a 9V PP3 battery.For high power applications, use a  9V DC power supply.
  • The preset R16 can be used to adjust the sensitivity of the receiver.
  • The frequency of the ultrasonic signal can be varied by adjusting the preset R17.Adjust it for optimum performance.


  1. Hi,
    NE555 pins 1 and 5 are mixed. Pin 1 should be GND.

  2. What is a good sub for the SK100 and SL100 matched transistors? The originals do not seem to be available and I have been searching the subs, but I cannot find a set that are evenly matched up.

    • I am going to try a TIP102 and TIP107 set. They are a bit over the top, but are matched and available. I have ordered these parts from Digi-Key and I’ll post the results when I get the circuit built.

  3. Theater application, Looking for a circuit to receive an audio que in a track to initiate a remote relay. Can anyone assist?


  4. Seetharaman, what is the Range between the Transmitter and Receiver.

    • seetharaman

      Hi Rex in the line of sight you can get between 20 to 50 feet depends on the supply, the set sensitivity and tuning of the frequency to match the transducer such that the performence is optimised.

  5. I need the modification of the circuit or rather an equivalent components.i’m from nigeria.

  6. when iam connecting an ultrasonic transducer at the astable output(pin3)
    output waveform is distorted pulse ie. pulse with ON and OFF. during ON time the pulse is distorted. what is the reason? is it becoz of transmitting of transducer?

  7. first of all, thank u alot ..

    i want to ask u if i can remove the relay , because i dont have another stage -I DONT WANT SWITCH-, i just want the output signal ,( i will connect it to a pic for display it on LCD) ..

    i hope u understand my point …

  8. Seetharaman

    Hi Kenneth it is for protecting the be junction of Q1 & Q2 from larger reverse bias, while out put of IC1 is swinging between + and – rail as their emitters are connected half the supply voltage through R4 & R5.

  9. what is the work of d1 & d2 of the ultrasonic transmitter?

  10. what is the work of d1 & d2 of the ultasonic transmitter

  11. Keep up the good work. I trust you would have actually made this circuit and checked it out.

    An modification is suggested. The output of the amplifier can be provided to a LM 3914 and the distance can be measured too. Could be useful while backing up the car.

  12. Good one. Keep it up. At the same time, I would like to suggest the following modification. After the signal at the receiver is amplified, we could effectively employ a LM 3914 to tweak the output to indicate the distance with a little calibration.

  13. sugiman/the-g-man

    mr seetharaman. if i want use it, to remote motorcycle to many function, how can i built it? i want to control ignition switch key/lock, electric starter, horn, turn light, and alarm from my simple ultrasonic remot. it’ll possible? tks

  14. Is this circuit working?? can anyone please help me………

  15. peace be upon u .

    Hello, is there anybody have tried this circuit ?
    it is working ?
    please , i need confirmation cause i gonna to use this circuit .

    Thankz for any feed back .

  16. Hellow guys! Am doing my min project cöncerning ultrasonic switch bt am facing the problem concrng the following cmpnt: relay switch 6volt 200 ohm, ceramic capacitor 560n, variable resistor 250k and 18k potentiometer, 680Pf, plz help me for the equivalent of these component if supply needed is 9v.

  17. please help me, i need a project write up on Ultrasonic switch

  18. Seetharaman

    Hi Sindhu the potential free contact of the relay RL1 can be used for any on off function. you can use it in the power supply feeding the transformer. be careful as the relay contacts now have 230 volts mains potential

  19. Can i use this circuit for ON and OFF the LEDs in the Automatic Emergency Light !!! Did any one tested this ?????PLzz reply mee…..

  20. Can i use this circuit for ON and OFF the LEDs in the Automatic Emergency Light !!!!Did any one tested ????Pzz tell me……….

  21. is it tested n verified………plz answer
    n do anyone has its pcb layout

  22. ok….i want buy the complete ultrasonic switch circuit..
    how can i buy it?

  23. seetharaman

    Hi Boy As I understand the above circuit is an ultrasonic remote “switch on” device( the device will be on till such time the ultrasonic wave is available at the receiver) the equipment will switch off once the ultrasonic wave stops at the input. hope my understanding is correct?!

  24. Do u know the function of ultrasonic switch ciccuit Seetharaman?

  25. Seetharaman

    Hi I have not yet tried the circuit. but I have few doubts. the emitter resistance of Q4 should be 1.5K, in the comparator R11, R13, D4 & R14 form a potential divider hence the voltage at inv input of IC1 will be >8 volt. Hence the DC should be blocked by providing a 100nF capacitor between Q4 collector and R13. Even R13 can be removed and linked to D4. Now D4 and D3 will act as a rectifier cum voltage doubler, when ever ultrasonic signal is received. You can connect Q5 collector itself to relay and delete Q6, as it serves no purpose. IC1 can be replaced with freely available TL071. I will try this circuit and give feed back.

  26. ok sekhar…i already add u at google talk
    talk there later…k thx

  27. who supplier circuit ultrasonic switch?
    can contact my number–> 0179321889
    i will buy your product

  28. hello,who can help me do this project name ultrasonic switch?who can help me?
    plz reply