Whisper detector. High sensitive wire bug. AVT 732 A series of "do-it-yourself" sets for beginners. The kit makes an incredible impression on the user. Low-pitched whispers or sounds, normally undetected by human hearing get amplified several-fold. The sound effects the user gets are unforgettable. Recommendations: the kit is recommended to people who are fond of listening to allegedly undetectable sounds, to people who are hard of hearing and for monitoring infant sleep. The kit is ideal for a variety of experiments related to amplifying different sounds. It may be of some use to people with hearing problems. It will probably turn out to be indispensable as a monitor of infant sleep. We hope it will also be highly appreciated by nature lovers.. Electrical characteristics • • • • • • built-in microphone headset or loudspeaker output smooth gain regulation frequency characteristics shaping battery-fed power supply 3…6VDC power supply AVT 732 Whisper detector. High sensitive wire bug. 1 Description The M1 electret microphone signal drives the U1A non-inverting amplifier. The gain set by the R5 and R6 resistors is constant and amounts to 23x (27dB). The pre-amplified signal is delivered to the inverting amplifier with the U1B IC. The negative value gain is determined by the ratio of the PR1 potentiometer and R2 resistances. It can be adjusted within the 0…1 range. The circuit is powered by single voltage while the R7, R8 and C5 components constitute a floating ground circuit. The C9, R2, C6 power supply filtering components as well as R1and C4 are necessary at high gain and they protect the circuit from self-oscillating caused by signals penetrating through power lines. The popular U2 TDA 7050 power amplifier is used. It works in the typical application mode as a 2channel amplifier with gain fixed at 20x (26dB). Figure 1. Schematic diagram Assembly and test The circuit schematic and the PCB layout is shown in figures 1 and 2. The components should be soldered to the PCB. The best way to do this is to follow the order of soldering given in the component list. The three wire jumpers should be soldered in first. During assembly a lot attention should be paid to the correct polarity of the components when soldering them in namely, the electrolytic capacitors, transistors and diodes. The pin 1 mark on the socket and IC must correspond to the component layout printed on the PCB. The handset plug and potentiometer must be connected as shown in the photo. Correctly connecting the potentiometer will cause the increase in volume while turning the volume knob clockwise. The electret microphone can be connected by short links of wire leads. This can also be done with the help of a long cable. In each case the correct polarity of the parts used must be observed (see the schematic and PCB). The negative terminal inside the microphone is connected to the metal can. After assembling the circuit it must be thoroughly checked that the components used have not been reversely soldered, that they are in their correct places and that the solder pads do not touch each other as this might lead to short circuits. After checking the correctness of assembly both the headset and the circuit can be plugged in. Once 2 AVT 732 Whisper detector. High sensitive wire bug. properly assembled, the amplifier will work instantly. Before using the circuit the potentiometer knob should be set at low volume (by turning it anti-clockwise) and then it should be gradually turned clockwise in order to increase volume. Too high gain will cause the circuit to oscillate (in the headset-to-microphone path) and screech unbearably. The circuit should operate when powered by the two AA or AAA batteries or even by a single 3V Li-Ion battery. It can also be powered from four batteries or from the 4.5…6V plug-type power supply. ATTENTION! The supply voltage should never exceed 6V! ! Figure 2. Components layout Component list In the order of soldering: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 below the U1IC wire jumper P2 - P3 connected by a wire jumper The boxes with drafts P4 - P5 connected by a wire jumper of pins and symbols of R1 - 1kW (brown-black-red-gold) the components used on R2 - 100W (brown-black-red-gold) the PCB as well as the R3 - 2,2kW (red-red-red-gold) photos of assembled sets may R4…R10 - 10kW (brown-black-orange-gold) come in useful. R5 - 220kW (red-red-yellow-gold) The U1 IC 8-pin socket! The U2 IC 8-pin socket! C10 - 470pF (also marked as 471) C1…C3 - 220nF (also marked as 0.22) C4…C9 - 100µF/6,3V (or higher voltage)! wire/connect the 10kW B potentiometer mount the knob on the potentiometer wire/connect the stereo headset (see the photo) wire/connect the electret microphone connect the battery snap-in terminal (red wire +; black wire -) to points P.O! insert the U1-LM358! insert the U2-TDA7050! connect the 3…6V power supply! AVT 732 Whisper detector. High sensitive wire bug. ! 3 1 2 3 4 The kit was made on the basis of a project bearing the same trade name published in "Elektronika dla Wszystkich" 12/04 www.elportal.pl The sale offer of our "do-it-yourself" sets is available on our website www.sklep.avt.com.pl Producer: AVT-Korporacja, Sp. z o.o. Leszczynowa 11 03-197 Warsaw fax: (+48 22) 257-84-55 phone.: (+48 22) 257-84-50 Poland 4 Technical Assistance Dept. Phone: (48 22) 257-84-58 firstname.lastname@example.org AVT 732 Whisper detector. High sensitive wire bug.