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This assembly is a real radar. Simplified to the extreme, it will alert you when an obstacle presents itself at a preset distance. For example, you can install it under the rear bumper of your car, powered by the reversing lights, it will warn you when you go back in your garage or during the execution of a niche ...

Before going into detail, let us look at the principle together. Ultrasounds are emitted which return after reflection to the obstacle and are detected. The return time is compared to a preset time. And if this time is lower, a buzzer is activated. This may seem complex, in fact, only two integrated circuits and two transistors are used! Clic is mounted in oscillator, it delivers pulses of 0.5 ms every 10 ms. Clib oscillates at the frequency of an ultrasonic piezoelectric transducer that sends wave trains. These waves are received by a transistor amp. P3 adjusts the polarization and sensitivity of the detection. Chc resets the RS flip-flop Cl2a / b and triggers the monostable Chd. P2 will set its time constant, hence the detection distance. The comparison is ensured by a second flip-flop RS whose output 11 goes to the high state if the reflection takes place before the end of the monostable time constant. C7 / R7 detect the absence of pulse. By connecting a voltmeter between Cl2b and the + of the power supply, the distance (to be calibrated) can be read. Cha will be tuned on the frequency of the piezo buzzer. (Possibly playing on R8)

Piezoelectric transducers are conventional, no special component here. We will of course respect the usual precautions concerning assemblies. The values ​​of the potentiometers have been calculated so that by placing the cursors at the center an average setting is adopted. We draw your attention to the necessarily restricted possibilities of this type of detector: ultrasounds have an unfortunate tendency to attenuate by moving away, and in addition reflection introduces a wave diffusion, so that the received signal is not Very important. Higher performance could have been obtained but at the cost of complex techniques. An editing that you can develop yourself, it would be necessary for example an amp whose gain varies as a function of time, or increase the transmission power. It's your turn !


Résistances 1/4W, 5%

R1 : 680 KR
R2,R13:47 KR
R3:56 KR
R4,R10,R12: 10 KR 
R7,R9: 1 M 
C1 : 47nF MKT 5mm
C2 : 470 pF céramique
C3: 22nF MKT 5mm
C4, C5, C8 : 2,2 nF céramique
C6 : 22 nF MKT 5 mm ou céramique
C7: 10nF MKT 5mm
C9, Ç10 : 1MF Tantale
CI1, CI2 : circuit intégré 4093 
CI3: régulateurs 8V: 78L08 
T1 , T2 : transistor NPN BÇ 238 B, 550 B, etc. 
D1, D2 : diode au silicium 1N 4148
PJ : 47 kR, potentiomètre ajustable vertical 
P2 : 100 kR, potentiomè­tre ajustable vertical 
P3 : 220 kR, potentiomè­tre ajustable vertical 
TP1, Tp2 : transducteurs piézo-électriques 
Un haut parleur piézo (buzzer)

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