Application circuit of 5-function remote control PT8A977/978

The toy remote control car uses servo motor wireless remote control technology. The basic requirements for remote control circuit design are high performance, low cost, smooth operation, flexible control, simple lines, and strong anti-interference ability. Usually the toy remote control car is driven by two micro DC servo motors to realize the forward, backward, left turn, right turn and acceleration functions of the toy remote control car. Competition in the toy remote control car market is becoming increasingly fierce, and higher and higher requirements have been placed on the electrical performance of toy remote control cars. The design of the wireless remote control circuit of the toy remote control car determines the overall performance of the toy remote control car. This article gives a design scheme for a mini toy remote control car circuit with excellent performance. The scheme is mainly designed using PT8A977/978 integrated circuit controller. 2 Remote control car wireless remote control circuit Ordinary toy remote control cars generally have the basic functions of forward, backward, left turn, and right turn. These functions can be completed by two micro servo motors, which have no speed regulation function. The schematic block diagram design of the wireless remote control circuit is shown in Figure 1. The circuit consists of two parts: wireless transmitting and wireless receiving. The wireless transmitting consists of a coding circuit and an RF transmitting circuit. The integrated circuit model used in the encoding circuit is PT8A977. This circuit has 5 encoding functions, among which F/B is used to control the forward and backward movement of the servo motor; L/R is used to control the left turn and right turn of the servo motor; turbo is used for accelerate. [url=../news_uploadimg/200511723528308.gif] The decoding circuit of the wireless receiving circuit part can be completed using the PT8A978 integrated circuit chip. The demodulated RF signal is amplified and filtered in the PT8A996, ​​and then the baseband signal is obtained. When the system samples the signal, the decoding logic can extract the F/B, L/R and function bits from the received signal, and at the same time output the corresponding control circuits for forward, backward, left turn, right turn and acceleration functions. flat. In order to meet the safety needs of toy remote control cars, an overload protection circuit should also be designed for the servo motor. 3. Main performance structure of PT8A977/978 PT8A977/978 is a supporting wireless remote control codec integrated circuit. They all have 5 pins, corresponding to 5 types of codec/decode functions. According to the difference in appearance and packaging, PT8A977/978 each has three serial numbers, and its series of products are listed in Table 1. PT8A977/978 has complete control functions of a remote control car. Their working voltage is 2.5~5.0V. When no function keys are pressed, the chip will automatically power off and the on-chip oscillator stops working, thereby reducing the working current. The coder/decoder is very simple to use and requires only a few external components to form a complete practical circuit. Table 1 PT8A977/978 series product introduction Coding model PT8A977BP PT8A977BW PT8A977BDE Package type 14-pin DIP 14-pin SOIC Bare chip coding model PT8A978BP PT8A978BW PT8A978BDE Package type 16-pin DIP 16-pin SOIC Bare chip 3.1 Coding circuit PT8A Performance structure encoding of 977BP/977BW The internal structure and outer packaging of the circuit are shown in Figure 2(a) and Figure 2(b) respectively. As can be seen from the figure: the interior of the encoder is mainly composed of input circuit, encoding circuit, oscillation circuit, timing generator circuit and output circuit. The input circuit has 5 input pins, which are respectively connected with the 5 function buttons forward (forward), backward (backward), right-ward (right), and leftw. ard (left) corresponds to turbo (accelerate). The encoding circuit in the chip sends digital codes to the two output pins SO and SC. The digital codes correspond to the defined function keys. The SO encoding output terminal is used for wireless remote control, while the SC encoding output terminal is used for infrared remote control. A counter in the on-chip sequential circuit enables the PT8A977BP/977BW to have an automatic power-off function. Its pin PC output can be used to control the on and off status of the external working power supply. Pressing any function button will immediately activate the chip. The encoding format and word format output by the encoder are shown in Figure 3(a) and Figure 3(b) respectively. In the encoding format, W1 represents the function code and W2 represents the start code. The pin function description of PT8A977/977BW is listed in Table 2. Table 2 Description of each pin of PT8A977BP/977BW Pin number Pin name Function description 1 Right With pull-up resistor, if this pin is grounded, select the right turn function 2 Test With pull-up resistor, this pin can be used for testing Mode 3 GND Negative pole of power supply 4 Backward has a pull-up resistor, grounding this pin selects the backward function 5 Forward has a pull-up resistor, grounding this pin selects the forward function 6 Turbo has a pull-up resistor, grounding this pin selects the acceleration function 7 SC With There is a coding signal output terminal with carrier frequency, used for infrared remote control 8 SO A coding signal output terminal with carrier frequency, used for wireless remote control 9 Vcc power supply positive terminal 10 PC power control output pin 11 OSCO oscillator output pin 12 OSCO oscillation Device output such as pin 13 NC is not connected to 14 Left and has a pull-up resistor. This pin is connected to ground to select the left turn function.