Implementation in hardware

Transmitting part

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Main technical data

The radio control system allows you to remotely control the toy at a distance of up to 10 meters.
The operating frequency of the transmitter is 27.12 MHz.
The transmitter power is within 4-10 mW.
The current consumption of the transmitter is not more than 20 mA.
The weight of the transmitter with antenna and power supply is not more than 150 g.
The sensitivity of the receiver in the operating frequency band is not worse than 100 μV.
The current consumption of the receiver is not more than 20 mA.
The weight of the receiver is not more than 70 g.
The command device provides the execution of four different commands, which are repeated periodically.
The weight of the command device is not more than 70 g.
The receiver and transmitter are powered by Krona-VTs batteries.

Principle of operation

The transmitter consists of a modulator and a high frequency generator (Fig. 1). The transmitter modulator is a symmetrical multivibrator assembled on low-frequency transistors VT2 and VT3 of the MP40 type.

The high-frequency generator is assembled on a transistor VT1 type P416 according to a capacitive feedback circuit. When the VT2 modulator transistor is open, the generator circuit closes to the positive of the battery, the generator is excited at the operating frequency, a high-frequency signal is emitted by the antenna.

The receiver consists of a high frequency stage, a low frequency amplifier and an electronic relay.

The high-frequency cascade of the receiver is a super-regenerator. The super-regenerator is assembled on a high-frequency transistor VT1 of type P416 (Fig. 2).

Fig.2

In the absence of a signal on the emitter chain C5 R3, oscillations in the quenching frequency are observed. The damping frequency determines the sensitivity of the super-regenerator at its operating frequency and is selected by elements C5, R3.

The command signal of the transmitter is selected by the L1-C4 circuit, amplified and detected by the super-regenerator. The R4-C8 filter passes the low-frequency command signal to the input of the VT2 amplifier, while separating the higher-order damping frequency.

The electronic relay is assembled on transistors VT3-VT4 of the MP40 type, and the collector of the VT4 transistor is connected to the executive relay KR of the PCM-1 type.

The low-frequency voltage of the command signal is amplified by transistors VT3-VT4 and fed through capacitor C13 to the rectifier cell UD1, UDZ.

The rectified voltage through the resistor R9 is supplied to the base of the transistor VT3. In this case, the emitter current of the transistor VT3 increases sharply, the transistor VT4 opens. The relay is activated, closing the power supply circuit of the command device motor.

The command device consists of an electric motor, a ratchet mechanism, a program disk and distributive sliding contacts. The program disk, the side of which is a system of jumpers, switches the power supply of the drive motors and other electrical elements of the toy through distribution sliding contacts.

Description of the electrical circuit of a radio-controlled toy

The diagram (Fig. 3) shows one of the options for the electrical equipment of a radio-controlled toy.

The toy has two drive motors that provide forward movement and turns left and right. The rear light bulbs of the toy serve as turn signals. Two headlights create the effect of illuminating the path of the toy.

Fig.3

To receive command signals from the transmitter, a receiver and a Command Apparatus are built into the toy. The engine of the drive and the command device, as well as the light bulbs, are powered by two series-connected batteries of the 3336L (U) (GB1) type. The receiver is powered by a battery "Krona-VTs" (GB2). To turn off the battery, a two-pole switch S is used. When a command signal is received from the transmitter, the relay KR, the receiver is activated and, with its contacts, turns on the electric motor of the command device (Fig. 4) MZ.

Fig.4. Command apparatus

The MZ electric motor, using a ratchet mechanism, rotates the program disk by 30 °, which corresponds to switching one command.

The program disk, through the distribution sliding contacts, turns on the electric motors of the drive and the light bulbs of the toy as follows:

In the "forward" position, contacts 1, 2, 3, 4 are closed, while the engines M1 and M2 are turned on, as well as the bulbs H1, H2, NC, H4.

In the "right" position, contacts 1, 2 are closed, while the M1 engine and the NC lamp are turned on.

In the "stop" position, all contacts are open.

In the "left" position, contacts 1, 3 are closed, while the engine M2 and the light bulb H4 are turned on.

Teams change periodically. The diagram shows the sequence of commands in one cycle.

Instructions for installation and commissioning of the system

It is desirable to place the receiver in the toy at the maximum distance from the email. motors and electromagnets. To protect the receiver from interference caused by electric motors, it is recommended to connect electrolytic capacitors 10-20 microfarads with an operating voltage of 10-12 volts in parallel with the electric motors, observing the polarity of the connection. An antenna must be connected to the receiver. A pin or wire with a diameter of 1.0-2.0 mm and a length of at least 20 cm can be used as an antenna. The antenna must be isolated from the body of the toy. As insulators, parts made of ceramics, fluoroplastic, plexiglass or polystyrene can be used. With an increase in the length of the antenna, the control range increases. The receiver must be covered with an insulating material to protect it from dust and moisture. The distance from the printed circuit board to the base on which the receiver is mounted must be at least 5 mm.
The location of the elements on the printed circuit board is shown in Fig.5.

After installing the electrical circuit and checking the performance (the switching order is indicated below), it is necessary to adjust the receiver to maximum sensitivity. The adjustment is made using capacitor C4 (see schematic diagram and drawing of the receiver). By turning the capacitor rotor with an insulating screwdriver, it is necessary to find the position at which the relay is activated when the toy is removed from the transmitter as far as possible.

The command apparatus is fixed on a horizontal platform with the help of paws.

List of radio elements

For radio control of various models and toys, discrete and proportional action equipment can be used. The main difference between proportional and discrete equipment is that it allows, at the operator's command, to deflect the model's rudders to any required angle and smoothly change the speed and direction of its movement, "Forward" or "Back". The construction and adjustment of proportional action equipment is quite complex and. not always within the power of a novice radio amateur. Although discrete action equipment has limited capabilities, but using special technical solutions, you can expand them. Therefore, further we will consider single-command control equipment suitable for wheeled, flying and floating models.

Radio controlled transmitter.

To control models within a radius of 500 m, as experience shows, it is enough to have a transmitter with an output power of about 100 mW. Transmitters of radio-controlled models, as a rule, operate in the range of 10 m. One-command control of the model is carried out as follows. When a control command is given, the transmitter emits high-frequency electromagnetic oscillations, in other words, it generates one carrier frequency. The receiver, which is located on the model, receives the signal sent by the transmitter, as a result of which the actuator is triggered. As a result, the model, obeying the command, changes the direction of movement or carries out one instruction pre-embedded in the design of the model. Using a single-command control model, you can make the model perform quite complex movements. The scheme of a single-command transmitter is shown in fig. 22.4. The transmitter includes a high frequency master oscillator and a modulator. The master oscillator is assembled on a transistor VT1, according to the capacitive three-point scheme. The L2..C2 circuit of the transmitter is tuned to a frequency of 27.12 MHz, which is assigned by the State Telecommunications Supervision Authority for radio control of models. The mode of operation of the generator for direct current is determined by the selection of the resistance value of the resistor R1. The high-frequency oscillations created by the generator are radiated into space by an antenna connected to the circuit through a matching inductor L1. The modulator is made on two transistors VT1, VT2 and is a symmetrical multivibrator. The modulated voltage is removed from the collector load R4 of the transistor VT2 and fed into the common power circuit of the transistor VT1 of the high-frequency generator, which ensures 100% modulation. The transmitter is controlled by the SB1 button included in the common power circuit. The master oscillator does not work continuously, but only when the SB1 button is pressed, when current pulses appear, generated by the multivibrato-

Rice. 22.4. Schematic diagram of the radio-controlled model transmitter

rum. The high-frequency oscillations created by the master oscillator are sent to the antenna in separate portions, the repetition frequency of which corresponds to the pulse frequency of the modulator.
The transmitter uses transistors with a base current transfer coefficient of at least 60. Resistors of the MLT-0.125 type, capacitors-K10-7, KM-6. The matching antenna coil L1 has 12 turns of PEV-1 0.4 and is wound on a unified frame from a pocket receiver with a tuning ferrite core of the brand 100NN with a diameter of 2.8 mm. The L2 coil is frameless and contains 16 turns of PEV-1 0.8 wire wound on a mandrel with a diameter of 10 mm. As a control button, you can use a microswitch type MP-7. The transmitter parts are mounted on a printed circuit board made of foil fiberglass. The transmitter antenna is a piece of steel elastic wire 0 1 ... 2 mm and about 60 cm long, which is connected directly to the XI socket located on the printed circuit board. All parts of the transmitter must be enclosed in an aluminum case. The control button is located on the front panel of the case. A plastic insulator must be installed at the point where the antenna passes through the housing wall to socket XI to prevent the antenna from touching the housing.
With known good parts and proper installation, the transmitter does not require special adjustment. It is only necessary to make sure that it works and, by changing the inductance of the coil L1, to achieve the maximum power of the transmitter. To check the operation of the multivibrator, you must turn on high-impedance headphones between the VT2 collector and the plus of the power source. When the SB1 button is closed, a low-pitched sound corresponding to the frequency of the multivibrator should be heard in the headphones. To check the operability of the RF generator, it is necessary to assemble the wavemeter according to the scheme of Fig. 22.5. The circuit is a simple detector receiver, in which the coil L1 is wound with wire PEV-1 1 ... 1.2 and contains 10 turns with a tap from 3 turns. The coil is wound with a pitch of 4 mm on a plastic frame Ø 25 mm. A DC voltmeter with a relative input resistance is used as an indicator.

Rice. 22.5. Schematic diagram of a wavemeter for transmitter tuning
10 kOhm/V or microammeter for current 50...100 µA. The wavemeter is assembled on a small plate of foil fiberglass with a thickness of 1.5 mm. Turning on the transmitter, place a wavemeter at a distance of 50...60 cm from it. With a working RF generator, the wavemeter needle deviates by a certain angle from the zero mark. By tuning the RF generator to a frequency of 27.12 MHz, shifting and expanding the turns of the L2 coil, the maximum deviation of the voltmeter needle is achieved. The maximum power of high-frequency oscillations emitted by the antenna is obtained by rotating the core of the coil L1. The transmitter tuning is considered completed if the wavemeter voltmeter at a distance of 1 ... 1.2 m from the transmitter shows a voltage of at least 0.05 V.
RC model receiver.

To control the model, radio amateurs quite often use receivers built according to the super-regenerator scheme. This is due to the fact that the super-regenerative receiver, having a simple design, has a very high sensitivity, on the order of 10...20 µV. The scheme of the super-regenerative receiver for the model is shown in fig. 22.6. The receiver is assembled on three transistors and is powered by a Krona battery or another 9V source. The first stage of the receiver is a super-regenerative detector with self-quenching, made on the transistor VT1. If the antenna does not receive a signal, then this stage generates pulses of high-frequency oscillations following at a frequency of 60 ... 100 kHz. This is the damping frequency, which is set by capacitor C6 and resistor R3. Gain you-

Rice. 22.6. Schematic diagram of a super-regenerative radio-controlled model receiver

of the divided command signal by the receiver's super-regenerative detector occurs as follows. Transistor VT1 is connected according to a common base circuit, and its collector current pulsates with a damping frequency. If there is no signal at the input of the receiver, these pulses are detected and create some voltage across the resistor R3. At the moment the signal arrives at the receiver, the duration of individual pulses increases, which leads to an increase in the voltage across the resistor R3. The receiver has one input circuit LI, C4, which is tuned to the frequency of the transmitter using the coil core L1. The connection of the circuit with the antenna is capacitive. The control signal received by the receiver is allocated to the resistor R4. This signal is 10...30 times less than the damping frequency voltage. To suppress interfering voltage with a quenching frequency, a filter L3, C7 is connected between the superregenerative detector and the voltage amplifier. At the same time, at the output of the filter, the voltage of the quenching frequency is 5...10 times less than the amplitude of the useful signal. The detected signal is fed through the isolation capacitor C8 to the base of the transistor VT2, which is a low-frequency amplification stage, and then to an electronic relay assembled on the transistor VT3 and diodes VD1, VD2. The signal amplified by the transistor VT3 is rectified by the diodes VD1 and VD2. The rectified current (negative polarity) is supplied to the base of the transistor VT3. When current appears at the input of the electronic relay, the collector current of the transistor increases and relay K1 is activated. As a receiver antenna, you can use a pin with a length of 70 ... 100 cm. The maximum sensitivity of the super-regenerative receiver is set by selecting the resistance of the resistor R1.
The receiver is mounted by printing on a board made of foil fiberglass with a thickness of 1.5 mm and dimensions of 100x65 mm. The receiver uses resistors and capacitors of the same types as the transmitter. The coil of the L1 super-regenerator circuit has 8 turns of PELSHO 0.35 wire, wound turn to turn on a polystyrene frame Ø 6.5 mm, with a tuning ferrite core of the 100NN brand with a diameter of 2.7 mm and a length of 8 mm. Chokes have inductance: L2 - 8 μH, and L3 - 0.07 ... 0.1 μH. Electromagnetic relay K1 type RES-6 with a winding with a resistance of 200 Ohm. Receiver tuning begins with a super-regenerative stage. Connect high-impedance headphones in parallel with capacitor C7 and turn on the power. The noise that appeared in the headphones indicates the correct operation of the super-regenerative detector. By changing the resistance of the resistor R1, maximum noise is achieved in the headphones. The voltage amplification stage on the VT2 transistor and the electronic relay do not require special adjustment. By selecting the resistance of the resistor R7, a receiver sensitivity of the order of 20 μV is achieved. The final adjustment of the receiver is made together with the transmitter. If you connect headphones in parallel with the winding of relay K1 and turn on the transmitter, then a loud noise should be heard in the headphones. Tuning the receiver to the transmitter frequency causes the noise in the headphones to disappear and the relay to operate.