This kit does not need any adjustments, if you follow the building instructions.


If they are used as part of a larger assembly and any damage is caused, our company bears no responsibility.

While using electrical parts, handle power supply and equipment with great care, following safety standards as described by international specs and regulations.

If it does not work

Check your work for possible dry joints, bridges across adjacent tracks or soldering flux residues that usually cause problems. Check again all the external connections to and from the circuit to see if there is a mistake there.

See that there are no components missing or inserted in the wrong places.

Make sure that all the polarised components have been soldered the right way round. Make sure that the supply has the correct voltage and is connected the right way round to your circuit. Check your project for faulty or damaged components.

If everything checks and your project still fails to work, please contact your retailer and the Smart Kit Service will repair it for you.


R1 =  180 KOhm C1, 6 = 10uF/16V TR1, 2, 3 = BC547 , BC548
R2 =  12 KOhm C2 = 47uF/16V P1 = 10 KOhm trimmer
R3, 8 =  47 KOhm C3 = 4,7 pF P2 = 47 KOhm trimmer
R4 =  3,9 KOhm C4, 7 = 1 nF IC1, 2 = 741 OP-AMP
R5, 6, 16 =  10 KOhm C5 = 10nF IC3 = 4093 C-MOS
R7, 10, 12, 14, 17 =  100 KÙ C8, 11 = 4,7 uF/16V R = TRANSDUCER 40KHz
R9, 11 =  1 MOhm C9 = 22uF/16V T = TRANSDUCER 40KHz
R13, 15 =  3,3 KOhm C10 = 100 nF D1, 2, 3, 4 = 1N4148
C12 = 2,2 uF/16V
C13 = 3,3nF
C14 = 47nF

How it Works

As it has already been stated the circuit consists of an ultrasonic transmitter and a receiver both of which work at the same frequency. They use ultrasonic piezoelectric transducers as output and input devices respectively and their frequency of operation is determined by the particular devices in use.

The transmitter is built around two NAND gates of the four found in IC3 which are used here wired as inverters and in the particular circuit 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 receiver similarly 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. The 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 output of IC2 changes abruptly and the Schmitt trigger circuit which is built around the remaining two gates in IC3 is triggered. This drives the output transistors TR1,2 which in turn give a signal to the alarm system or if there is a relay connected to the circuit, in series with the collector of TR1, it becomes activated. The circuit works from 9-12 VDC and can be used with batteries or a power supply.

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