This article describes the legacy of this article reminded alarm compact, external dimensions of 17 × 35 × 100mm, like two match boxes, control distance of 1-5m (can be raised to 15m), the alarm sound loud and clear, low power consumption, frequency stability, low cost, easy to make, it is suitable for carry out important items to prevent the owner, can also be used to monitor a child walking, those interested may wish to try.
The device is a transmitter and receiver system composed of two parts, work in the frequency modulation (FM) band. Principle of the transmitter circuit shown in Figure 1 (Click to download the schematic diagram ). It is by the transistor VT1, VT2 and its peripheral components, the multi-harmonic oscillator, its frequency is about 1000Hz, the signal out through the capacitor C3 to modulation by the VT3 and LC components, the FM oscillator, the FM signal modulated output from the C10, through the miniature antenna inside the space radiation. One is the role of C6 plus broadband and can effectively prevent human induced effects on the frequency.
Principle of the receiver circuit shown in Figure 2 (Click to download the schematic diagram ). Transistor VT1 and its components from the LC circuit composed of super-regenerative receiver, issued by the FM transmitter to receive signals. Gates A, B, C constitute a signal amplification circuit, the received signal amplification, comparison, fell quite different control gate D, E oscillator circuit composed of 1Hz, and then inverting the output of gate F to control the transistor VT2, VT3 composed of complementary audio oscillator.
When the receiver to the transmitter signal, the output of gate C is positive, diode VD turn, the door D, E composed of low-frequency oscillator to stop, the door F output is low, VT2, VT3 complementary stops the oscillator, the speaker BL is not sound.
When not receiving the transmitter signal that the target or children to leave the host 1-15m, low output of gate C, VD closing, gate D, E form of low-frequency oscillator, inverting gate output frequency F 1Hz complementary positive impulse control oscillator circuit issued a hasty "beep ... beep ..." sound to remind the owner of attention until the target can be controlled from within the child back, the alarm automatically stops.
Selection and production of components
Parts list below.
Transmitter section
Number Name Type the number of R1, 4 resistance 20K2R2, 3 resistance 100K2R5 fine tuning resistance 100K1R7 91K1R6 resistance resistance resistance 51K1R8 470O1C1, 2 ceramic capacitors ceramic capacitor 0.01u2C4 0.005u1C5, 6 ceramic capacitor ceramic capacitor 0.1u1C8 33P2C7 ceramic capacitors 30P1C9 Ceramic capacitor tuning 10-3P1C10 51P1L inductance ceramic capacitors made (see table after the text) 1VT1, 2 Transistor Transistor 90181S 90112VT3 miniature toggle switches switch 1E battery 3V1
Receiver section
Number Name Type Number Number Name Type Number R1 resistance 4.7K1C12 electrolytic capacitors 1u1R2 tuning resistor 200K1C13, 14 ceramic capacitor electrolytic capacitor 0.1u1R3 resistance 470O1C15 10u1R4, 5,7 fine-tune the resistance of resistor 1M3D 100K1VT1 diode IN41481R6 trim resistor 51K1VT2 transistor transistor 90181R8 90131R9 fine-tune the resistance 510O1VT3 90121R10 resistance transistor gate IC CD40691R11 100K1IC six non-inductive resistance 750O1L1 L11C1 with ceramic capacitors transmitter 15P1L2 color code inductance inductance 6.5um 1C2, 3 ceramic capacitors ceramic capacitor 1C4 33P2BL 0.005u1S small speaker small dial switch Activity 1C5 ceramic capacitor 0.5u1E battery 3V1C6-11 ceramic capacitors 0.01u6
To reduce the size, the resistance of micro-components used in all 1/16W, ceramic capacitors and electrolytic capacitors used in all narrow-type, BL using micro-electromagnetic information F12mm Xiangqi. Transmitter coil inductor L1 with F1mm enameled wire around the pencil in the F7.5mm 3 laps, bodiless made. L1 receiver and transmitter coil inductor L1 in the same. Transmitter and receiver of the two sections of the 5 batteries. Selected components will directly affect the quality of the electrical properties of the device, welding is completed, check the confirmation, power can be debugged. FM radio transmitter used to adjust, so that in the low frequency radio transmitter to receive signals from local FM radio stations should pay attention to avoid, careful adjustment of the transmitter circuit R5, R6, C9, and gradually opened to receive the distance, so that received the loudest, the transmitter to the minimum operating current of about 0.3mA or so far.
Then adjust the right to adjust receiver transmitter, the receiver off the electromagnetic hearing Xiangqi BL, access high-impedance headphones, carefully adjusted R2 and the transmitter of the variable capacitor C9 (avoid the attention of local radio stations), transmitter in the headset to hear the loudest, clearest, and then gradually pulled away from the two planes, and then adjust the monitor to the desired distance of R6, when gate C the output voltage of about 1.5V. Turn off the transmitter, the measured output of gate F should be 3V pulse, adjust R7, C12 can change the pulse width. Open the transmitter, F strain output 0V. Then turn off the transmitter, the electromagnetic information access Xiangqi BL, should be given intermittent "beep ... beep ..." sound. Silent or sound, such as small, should be carefully adjusted R8, R9, R11 and C13, C14, so that the maximum sound the alarm. Measured operating current is about 70mA this time around. Open the transmitter, set the tone should be audible from within the BL, the current waiting time of about 0.5mA.
The machine work on the FM band, the actual control of distance and location of the two machines, the environment and the degree of resistance barrier. Receiver can not foil cigarettes and other large metal objects placed together, we can not hand hold high positions, otherwise they will drift out of control because of the frequency.