Duty cycle wireless remote control circuit diagram

Working principle Figure 1 shows the remote control transmitting circuit. The 555 integrated block and R1, R2, W1, D1, D2 and C1 form an astable wide-range variable duty cycle oscillator. The oscillation frequency of the parameters shown in the figure is about 50Hz. By adjusting the resistance of W1, the duty cycle ranges from 1% to 99%, and a 50Hz square wave signal is output from pin ③. VT1 and its peripheral components constitute a crystal frequency-stabilized capacitor three-point oscillator with a resonant frequency of 27.145MHz. The high-frequency carrier wave generated by VT1 oscillation is modulated by the square wave signal output by pin 555③ and is emitted by the antenna.

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Figure 2 shows the receiving drive circuit. In order to simplify the receiving circuit, a super regenerative detector is composed of VT2 and its peripheral components. It detects the original square wave modulated signal and sends it to the ③ pin of IC2 through C12 and R7. The amplified signal is D3 and D4 voltage doubler rectifier, and the VT3 emitter follower outputs its smoothed DC voltage. The size of this voltage is related to the different duty cycle signal waveforms sent. 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; conversely, the motor speed is slow. When the duty cycle is small enough, VT3 cuts off and has no output, VT4 does not conduct due to loss of bias, and the motor stops. From this, the motor speed is proportional to the duty cycle.

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Component selection L1 can use a 10K type mid-circumferential bobbin, and use ∮0.15mm high-strength enameled wire to wind 9 turns. L2 uses the same type of enameled wire to wind 3 turns on the outer layer of L1. No shielding cover is needed, but the magnetic core needs to be screwed in; Production of L3 Same as L1; BC uses JA12 and other metal shell resonators, the frequency is between 27 and 29.8MHz; 3DG130D type NPN transistor, β>100, RFC uses 18μH color code inductor.

Circuit debugging first adjusts the transmitter carrier frequency oscillator, high-frequency choke coil RFC and crystal oscillator BC are not installed for the time being, short-circuit C4 to ground, adjust the resistance of R3 so that the C pole current of VT1 is 12mA, and then install the crystal oscillator BC , at this time the current should increase to about 15mA. Otherwise, carefully adjust the magnetic core of L1 until the circuit starts to oscillate. Remove the C4 short circuit. The debugging method of super regenerative detection is to use an 800Ω high-impedance earphone in series with a 10μF capacitor across VT2. Between the e and c poles, use a non-inductive screwdriver to finely adjust the potentiometer W2 and the magnetic core of the coil L3 until there is an obvious and loud "rustling" sound in the headphones. The next step is to bring the transmitter antenna close to the receiver, turn on the remote control switch K, and fine-tune the magnetic cores of the coils in the transmitter and receiver until clear industrial frequency sound can be heard in the headphones, then distance the two machines, and then go further Fine tune. The remaining circuits do not require debugging.

Experiment comments:

Taking R6 as 200Ω and actually connecting the circuit, the functions described in the article can be achieved. However, during the actual production process, it was found that it is difficult to align the two frequencies when making inductors, but it can be easily solved according to the method described in the article. If an oscilloscope (100Hz) is used during the debugging process, the effect will be better. This circuit has a reasonable structure and can be extended to other circuits, making it suitable for radio enthusiasts to make.