Production of wireless proportional remote control circuit

1. Working principle of motor remote control circuit
Figure 1 is the remote control transmission circuit. The 555 integrated circuit and R1, R2, RP1, VD1, VD2 and C1 form an astable large-range variable duty cycle oscillator. The oscillation frequency of the parameters shown in the figure is about 50Hz. By adjusting the resistance value of RP1, the duty cycle can vary from 1% to 99%, and a 50Hz square wave signal is output from pin ③. VT1 and peripheral components form a crystal frequency-stabilizing capacitor three-point oscillator, and the resonant frequency of the quartz crystal is 27.145MHz. This circuit uses quartz crystal frequency stabilization, so it works reliably. The high-frequency carrier generated by VT1 oscillation is modulated by the square wave signal of pin ③ of the 555 circuit and transmitted by the antenna.

Wireless remote control receiving circuit

Figure 2 is the receiving drive circuit. To simplify the receiving circuit, VT2 and its peripheral components form a super regenerative detector to detect the original square wave modulation signal. C12 and R7 are added to the ③ pin of IC2 for amplification. The amplified signal is rectified by VD3 and VD4, and the VT3 emitter follower outputs a smooth DC voltage. The magnitude of this voltage is related to the waveform of the signal with different duty cycles sent. When the duty cycle is large, the voltage is high, the bias current provided to VT4 through R11 is large, and the motor speed is high; when the duty cycle is small, the voltage is low, the bias current provided to VT4 through R11 is small, and the motor speed is slow. When the duty cycle is small enough, VT3 is cut off and has no output, VT4 is not turned on due to loss of bias, and the motor M stops. It can be obtained that the motor speed is proportional to the duty cycle.

2. Selection of components
L1 can use 10K type medium-circle frame, with Φ0.15 high-strength enameled wire wound 9 turns, L2 is wound 3 turns with the same type of enameled wire on the outer layer of L1, without shielding cover, but needs to be screwed into the magnetic core. L3 is made in the same way as L1. B uses metal shell resonator such as JAl2, with a frequency between 27-29.8MHz. VT1, VT2, and VT3 all use 3DG130D type NPN triode, β>100. VT4 uses 3DD15D type high-power tube. RFC uses 18uH color code inductor. IC1 model is NE555. IC2 model is LM386. Except for the electrolytic capacitors indicated, all capacitors use CC1 type high-frequency ceramic capacitors. All resistors use 1/8w carbon film resistors.

3. Circuit debugging
First adjust the carrier frequency oscillator of the transmitter, and do not install the high-frequency choke coil RFC and crystal oscillator B for the time being, so that C4 is short-circuited to the ground. Adjust the resistance value of R3 so that the collector current of VT1 is 12mA, and then install crystal oscillator B. At this time, the current will increase to about 15mA, otherwise the magnetic core of L1 should be carefully adjusted until the circuit starts to oscillate, and remove the short-circuit line of C4. The debugging method of super-regenerative detection is to use a 800Ω high-impedance headset in series with a 10uF capacitor across the emitter and collector of VT2, and use a non-inductive screwdriver to fine-tune the potentiometer RP2 and the magnetic core of the coil L3 until there is a clear and loud "rustling" sound in the headset. The next step is to bring the transmitter antenna close to the receiver, turn on the control switch S, and fine-tune the magnetic core of the coil in the transmitter and receiver until a clear power frequency sound can be heard in the headset, then pull the distance between the two machines, and further fine-tune. The rest of the circuit does not need to be debugged, and it can generally work normally after installation.