Anti-lost alarm circuit diagram consisting of wireless transmitter circuit and wireless receiving alarm circuit

Photocoupler

The anti-lost alarm introduced in this example consists of a wireless transmitter circuit and a wireless receiving alarm circuit. When the distance between the wireless receiving alarm and the wireless transmitter exceeds 3m, the wireless receiving alarm will sound an alarm. The device can be used for anti-lost alarms of important items such as bags, wallets, folders, etc., and also prevents children from losing when they play.

Circuit working principle

The wireless transmitter circuit consists of a low frequency oscillator and a high frequency oscillator as shown. The low frequency oscillator is composed of resistors R1, R2, capacitors Cl, C2 and time base integrated circuit ICl; high frequency oscillator consists of variable resistor RP, inductor L1, resistor R3, R4, capacitor C3-C9, and transmitting antenna Wl and transistor Vl are composed as shown.

The wireless receiving alarm circuit is composed of a wireless receiving processing circuit and an alarm circuit. The wireless receiving buried circuit is composed of a wireless receiving integrated circuit IC2 and a capacitor ClO-Cl9; the alarm circuit is composed of a sound effect integrated circuit IC3, a transistor V2, a resistor R5, a diode VD and a speaker BL.

After the low frequency oscillator oscillates, the oscillating signal of 1 kHz is output to modulate the high frequency oscillator, and the modulated high frequency signal is transmitted to the air through the antenna W1.

When the distance between the wireless receiving alarm device and the wireless transmitter is within 3 m, the antenna W2 receives the high frequency modulated signal transmitted by W1, and sends it to IC2 for decoding and demodulation processing, so that the 2 pin of IC2 outputs a low level. IC3 can't trigger work, BL doesn't sound.

If the distance between the wireless transmitter and the wireless receiving alarm exceeds 3m, the wireless receiving alarm will not receive the high-frequency modulation signal transmitted by W1, and the 2 pin of IC2 outputs a high level, so that lC3 is triggered to work, and its output is After the audio signal is amplified by V2, the BL is driven to sound an alarm.

To prevent the loss of the bag or prevent the child from being lost, the wireless transmitter can be placed in the bag or in the child's pocket, the wireless receiving alarm is placed on the owner of the bag or the guardian of the child; the anti-theft alarm for the wallet can be The wireless receiving alarm is installed in the wallet and the wireless transmitter is placed on the owner. Once the loss occurs, the anti-theft item immediately sounds an alarm, which is convenient for finding and searching.

Component selection

Rl-R5 selects 1/4W metal film resistor for use.

Rp uses organic solid variable resistors.

Cl-C4, Cl5 and C18 use monolithic capacitors or polyester capacitors; C5, C7-C14, CI**C17 select high-frequency ceramic capacitors or glass glaze capacitors; C**Cl9 selects ceramic fine-tuning capacitors.

VD selects 2CPlO type silicon common diode or 1N4007 type silicon rectifier diode.

Vl selects S9018 type silicon NPN high frequency transistor; V2 selects S8050 type silicon NPN transistor.

ICl selects NE555 type time base integrated circuit; IC2 selects TDA7000 type wireless receiving integrated circuit; IC3 selects KD9561 type alarm sound effect integrated circuit.

Ll is entangled into a hollow coil by φlmm enameled wire on a φ7.5nm cylinder, and L2 is entangled into a hollow coil by φ0.5hnln enameled wire on a φ5mm cylinder.