Transmitting circuit: a self-excited multivibrator composed of discrete components, whose oscillation frequency is mainly determined by L2 and C3. The elements in the figure can obtain the emission frequency of 30 ~ 40 MHz. Usually, the circuit is off. After pressing AN, the power supply is turned on and the circuit sends out an oscillation signal.
Receiving circuit: D 1 and D2 form a voltage doubler circuit to double rectify the signal induced by L4, and its output signal can make BG3 saturated and conductive. The negative pulse generated by its conduction sets the 555 time base circuit, 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 doorbell (2)
principle of operation
As shown in figure 1, the transmitting circuit is boosted by an, L5 and BG5 oscillation, rectified by D3, filtered by C 15 and c 16, and the d c of 1.5V is raised to 12v to supply power for the transmitting circuit. A series of digitally coded pulse signals generated by IC4 are amplified by BG4 and radiated by L3 loop. An LED is an indication of the emitted signal.
The receiving circuit is shown in Figure 2. The receiving circuit with BGl as the core amplifies the radio signal on the inductor L2, outputs a pulse voltage from the collector, and adds it to the base of BG2 through R4 and c6 for re-amplification. Ic 1 is shaped and amplified again, and directly added to IC2 for decoding. Pin 13 of IC2 changes from low level to high level, which triggers Ic3 music integrated circuit and makes the speaker ring the "Ding Dong" doorbell.
Manufacturing and debugging
In order to make the remote control distance farthest and ensure stable and reliable operation, 14 and L 1 (rounded corners) are directly made on the circuit board. Measure the components with multimeter before welding, and the welding position of the components shall be accurate according to the schematic diagram. Pay attention to components with polarity and components with similar appearance.
Put the transmitter near the receiver, press an, and you should hear the "Ding Dong" doorbell. Open the launch distance and fine-tune c2 (with a non-inductive pen) to make the remote control distance the farthest. Adjust C2 bit by bit to avoid damaging components.
In order to make the products not interfere with each other, the debugged products should be coded by themselves. Note that the codes of pins 1 ~ 8 of IC4 and IC2 should be exactly the same (connected to positive power supply or grounded or suspended).
Circuit diagram of remote control doorbell (3): wireless coding remote control doorbell circuit
1. Remote coding doorbell transmitting circuit
The above picture is a schematic diagram of the transmitting circuit of the coded remote control doorbell, which consists of two parts: the transmitting circuit and the switch modulation coding circuit. The transmitting circuit consists of oscillator circuits L 1, C 1 and oscillator transistor VT 1. The oscillator adopts an inductive three-point oscillating circuit, the oscillating coil L 1 is a U-shaped copper-clad strip on the printed circuit board, the tuning capacitor C 1 is connected in parallel at both ends of the U-shaped copper-clad strip, and the tap L 1 is connected to the positive pole of the power supply GB through the high-frequency choke L2 and the button switch S, which is equivalent to the grounding in the equivalent circuit of the high-frequency oscillator; One end of the oscillating coil is connected with the collector of VTI, and the other end is positively fed back to the base of VT 1 through capacitor C2, thus forming an inductive three-point oscillating circuit. The feedback size of the oscillator is determined by the partial pressure between C2 and C3 and the capacitor between the electrodes of the oscillating tube VTI. The oscillation frequency is mainly determined by the inductance of L 1 and the capacitance of C2 and C3. Changing C 1 can adjust the oscillation frequency. L 1 adopts copper-clad strip structure, which will not deform, increase the stability of oscillation frequency, and also has the function of transmitting antenna. R 1 is the bias resistance on VT 1. When the coded output Dout of the coded integrated circuit IC 1 is at a high level, the UHF oscillator oscillates, and when it is at a low level, it stops oscillating and performs switching modulation. The modulation and coding circuit consists of coding integrated circuit IC 1 etc. Usually, when the product leaves the factory, both the address coding setting terminal and the control data coding setting pedal are in a suspended state and become 12-bit address 0 data coding. In use, the coded signal should be preset. Generally, an address coding area is reserved on the printed circuit board, which consists of three rows of pad holes. Three states are selected by welding, namely floating, connected to the positive pole of power supply or grounded. The address codes of the same transceiver system must be consistent, and different devices must be set with different address codes to prevent mutual interference between systems. In addition, the oscillation resistance of the codec integrated circuit must be matched. When the oscillation resistance R2 of the encoded PT2262 is1.2mΩ, the oscillation resistance of the decoded PT2272 is 220kΩ；; If R2 is 4.7 mω, the decoding oscillation resistance corresponds to 820 kω. If the oscillation resistance of the codec integrated circuit does not match, the sensitivity of the remote controller will be greatly reduced, or even the control function will be lost. When the coding start of the coding integrated circuit is grounded (at a low level), the encoder outputs a coding signal, and when the power switch S is turned on, a remote control signal will be sent out. The resistor R3 and the light emitting diode VD form an indicating circuit to indicate the working state of the remote controller.