Circuit diagram of remote control doorbell (1)

Transmitting circuit:The self-excited multivibrator is composed of discrete components, and its oscillation frequency is mainly determined by L2 and C3. The transmission frequency of 30-40mhz can be obtained from the components in the figure. At ordinary times, the circuit is in the off state. After pressing an, the power is connected and the circuit sends out oscillation signal.

Receiving circuit:D1 and D2 constitute a voltage doubling circuit, which rectifies the signal induced by L4. The output signal can make BG3 saturated conduction, and the negative pulse generated by the conduction makes 555 time base circuit set, and its three pins output high level to trigger the music integrated circuit IC2 to work. BG4 is used for audio power amplification. R3 and C9 adjust the delay time of 555.

Circuit diagram of remote control doorbell (2)

working principle

The transmitting circuit is shown in Figure 1. The voltage is boosted by oscillation of an, L5 and bg5, rectified by D3, filtered by C15 and C16, 1.5V DC is raised to 12V DC to supply power to the transmitting circuit. IC4 generates a series of digital coded pulse signals which are amplified by BG4 and radiated by L3 loop. LED is the indication of transmitting signal.

The receiving circuit is shown in Figure 2. The receiving circuit with BGL as the core amplifies the radio signal on inductance L2, outputs a pulse voltage from the collector, and then adds it to the base of BG2 through R4 and C6 for further amplification. The ICL is reshaped and amplified again and directly added to IC2 for decoding. The 13 pin of IC2 changes from low level to high level, triggering IC3 music integrated circuit to make the horn emit “Ding Dong” doorbell.

Production and commissioning

In order to make the remote control distance farthest and ensure stable and reliable operation, 14 and L1 have been directly made on the circuit board (rounded). Before welding, the components shall be measured by multimeter, and the welding position of components shall be accurate according to the schematic diagram. Pay attention to the components with polarity and components with similar shape.

Put the transmitter close to the receiver, press an to hear the “Ding Dong” door bell, open the transmitting distance and fine tune C2 (with a non sensitive pen) to make the remote control distance the farthest. Adjust C2 just one by one to avoid damaging the components.

In order to avoid mutual interference between the products, the debugged products should be coded by themselves. It should be noted that the 1-8 PIN codes of iC4 and IC2 should be completely consistent (the positive power supply, grounding or hanging should be consistent).

Remote control doorbell circuit diagram (3): wireless coding remote control doorbell circuit

1. Remote coding doorbell transmitting circuit

The above figure shows the circuit schematic diagram of the remote control doorbell transmitter, which is composed of two parts: the transmitting circuit and the switching modulation coding circuit. The transmitting circuit consists of oscillation circuit L1, C1 and oscillating triode VT1. The oscillator adopts inductance three-point oscillation circuit, oscillation coil L1 is U-shaped copper coated strip on printed circuit board, tuning capacitor C1 is connected in parallel at both ends of U-shaped copper strip, L1 tap is connected with positive pole of power supply GB through high-frequency resistance coil L2 and button switch s, which is equivalent to grounding in equivalent circuit of high-frequency oscillator; one end of oscillation coil is connected with VTI collector, and the other end is fed back through capacitor C2 To the base of VT1, the inductor three-point oscillation circuit is formed. The feedback size of oscillator is determined by C2, C3 and voltage divider of VTI. The oscillation frequency is mainly determined by the inductance of L1, the electric capacity of C2 and C3, and the oscillation frequency can be adjusted by changing C1. L1 adopts copper coated structure, which will not deform, increases the stability of oscillation frequency, and also has the function of transmitting antenna. R1 is the upper bias resistor of VT1. When the dout of coding IC 1 is high level, the UHF Oscillator will oscillate, and the oscillation will stop at low level, and switch modulation will be carried out. Modulation and coding circuit is composed of coding integrated circuit IC1, etc. usually, when the product leaves the factory, the address code setting terminal and control data coding setting are in the suspended state, and become 12 bit address 0 data code. In use, the coded signal should be preset. Generally, the address code area is reserved on the printed circuit board, which is composed of three rows of pad holes. The mode of solder overlap welding is used to select the three states of hanging, power supply positive or grounding. The same set of receiving and transmitting system address codes must be consistent, and different equipment must be set with different address codes to prevent mutual interference between systems. In addition, the integrated circuit oscillator resistor must be matched. When the encoding PT2262 oscillation resistor R2 is 1.2m Ω, the decoding PT2272 oscillation resistor is 220K Ω; if R2 is 4.7m Ω, the decoding oscillation resistor is 820k Ω. If the oscillator resistor of the codec integrated circuit is not matched, the sensitivity of the remote controller will be greatly reduced, and even the control function will be lost. When the encoding IC code starts to kick the ground (at low level), the encoder outputs the coded signal. When the power (transmitting) switch S is connected, the remote control signal will be sent out. Resistor R3 and led VD constitute the indicator circuit to indicate the working state of the remote controller.

2. Remote coding doorbell receiving circuit

The figure above shows the circuit schematic diagram of the coded remote doorbell receiver, which is composed of four parts: super regenerative detection circuit, amplification circuit, decoding circuit and music doorbell circuit. The super regenerative detection circuit is composed of UHF Transistor vt2, resonant coil L3, resonant capacitor C6, feedback capacitor C5, etc. its oscillation frequency mainly depends on L3, C6 and C5, and the oscillation intensity is determined by the capacity of C5. Changing C6 can change the receiving frequency. In the process of establishing UHF oscillation, the high-frequency current in L3 and C6 oscillation circuit will charge C7 through C5 and vt2 interelectrode capacitance. The voltage on C7 will rise and produce reverse bias voltage, which will be applied to the transmitting junction of vt2. The DC operating point of vt2 will move down rapidly to weaken the high-frequency oscillation until vt2 stops and the oscillator stops oscillation. After that, the charge charged by C7 is discharged through resistor R4, and the reverse bias voltage of vt2 decreases until the forward bias of transmitting junction meets the high-frequency oscillation condition, and then the next oscillation process is established, thus forming UHF oscillation modulated by intermittent oscillation, which is quenching oscillation. When the amplitude is large, the initial level is high, the oscillation process is established quickly, and the interval time of each oscillation is also short. Because vt2 works in the nonlinear region close to the cutoff, the emitter current formed after detection is also large, and the voltage drop on resistor R5 is also large. On the other hand, when the amplitude of the received UHF signal is small, the voltage drop generated on R5 is also small. Therefore, the audio voltage consistent with the modulation digital signal is obtained at R5, which is called super regenerative detection. Because the super regenerative geophone is in the intermittent oscillation state, it has high sensitivity of receiving and detecting, and has ten thousand times amplification gain. In Figure 4, L2 is a high-frequency choke coil, which prevents the high-frequency oscillation current from directly entering the ground, and can establish the working point of the oscillator through the DC signal. Bias resistor R5 and bypass capacitor C8 provide a stable static operating point for vt2 base. The output signal from vt2 collector is filtered out by high-frequency resistor L2 and filter capacitor C9 to generate data signal voltage drop on collector load resistor R7. Thermal noise and residual quench oscillation signal generated by super regenerative detector are removed by filter resistor R6 and filter capacitor C11, and input to the base of pre voltage amplifier VT3 through coupling capacitor CIO.

The amplifier circuit is composed of three-stage amplifier, in which the voltage negative feedback amplifier circuit is composed of VT3, R8 is the negative feedback bias resistor, and R9 is the collector load resistor. The amplified signal is transmitted to the base of vt4 by coupling capacitor C12. A two-stage direct coupled amplifier is composed of vt4 and vT5. The amplified signal is output by vT5 collector and loaded to the 14 pin DIN terminal of the data signal input terminal of the decoding chip IC2. When the level reaches 2V, the decoding chip acts.

Circuit diagram of remote control doorbell (4)

In the figure, a and B inverters in six inverter 406 and crystal X1 constitute a 32.768KHz signal generator. Then, the inverter C, D, e and F are driven in parallel to modulate the high-frequency signal generator with Q1 as the core, and output high-frequency amplitude modulation wave. Q1 and other elements in Fig. 2 constitute a super regenerative receiving circuit to receive the high-frequency signal from the transmitter and demodulate 32.768KHz The signal is coupled by C4 and R3, amplified and shaped by inverter a, B, C, and then filtered by crystal x1, and then triggered by Q2 to send out “Ding Hu” doorbell. The effective control distance of the remote control doorbell is about 40 meters.

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