Place the alarm in the carried item. When you forget the placement of the item, or leave yourself in your own place. The alarm will issue an alarm.
The alarm is divided into two parts. Part of the UHF transmitter and the other part is the AM hypercurrent receiver.
Transmitter circuit
The UHF transmitter circuit consists of the transistor TR1 and the peripheral element constituting a deformable Colez LC oscillating circuit generates a 314 MHz carrier. The coil L1 serves as an emission antenna, which is made of a single copper wire; if it is mass production. The copper foil can be etched on the plate. TR1 is selected from the transistor above FT = 600 MHz. CT1 is a ceramic semi-variable capacitor for adjusting the oscillation frequency. Non-metallic "one" shaped screwdriver is required. It can be cut with bamboo chopsticks. In order to prevent the impact of stray capacitance, the value of C1 can be ensured that it can be guaranteed. In Fig. 1, the C1 and the stray capacitance and about 5 pF.
The CMOS inverting circuits IC1A, 1B constitute an RC oscillator generates a 2 kHz modulation wave, which outputs the base of the TR1 to form a bias voltage after the IC1C buffer and D1 rectify. The modulation waveform is turned about 268ns from the start of "H" to the oscillation. The frequency of modulation waves cannot exceed 3.7 MHz.
Due to the high circuit frequency, pay attention to the components in the oscillation circuit are installed in the shortest distance.
2. Receiver circuit
The receiver uses a super regenerative circuit, as shown in Figure 3. Transistor Tr2 and peripheral components constitute a hyperbuplex demodulation circuit. L1 and C5 are oscillating components, intermittent oscillation frequency is about 1.7 MHz; L2 and CT1 are tuning elements. The size of the coil L2 is shown in Figure 4.
Inverters IC2A, B receive a linear amplifier, amplify the detection output (about 100 mV) to the logic level (3V), so that the rising edge of the demodulated waveform is very steep. Diodes D3, D4 are peak detection, and the signal is discriminated by the threshold of IC2C.
IC2E, 2F is connected to an RC oscillator. The oscillation frequency is the same as the resonant frequency of the piezoelectric buzzer. Decided by R2, C1; when IC2C is output to "H". The oscillation output is driven by the IC2D drive piezoelectric buzzer. Alert sound.
3. How to use
When used to prevent loss or anti-theft. Place the transmitter in the item and enable the switch "ON", the receiver carries it. When the item is left, it is a certain distance. The receiver starts an alarm due to the radio wave.
When used for searching for items, place the receiver in the item, the transmitter carries it. If you forget the placement place, just turn off the transmitter power. The receiver in the item will make a alarm.
The interaction distance of the transmitter and receiver is about 15 m. , Reading the full text, the technology area
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