Design of TV transmitter control unit based on S3C2440

0 Introduction

With the development of radio and television, the application of TV transmitter technology is becoming more and more extensive. In order to effectively ensure the quality of TV signals, the importance of TV transmitter monitoring is more prominent. This paper gives a design method for intelligent control of TV transmitters using S3C2440 by monitoring TV transmitter signals. This method can also be connected to the host computer and use PC monitoring computer to achieve telemetry and remote control.

1 System composition

This controller uses the ARM9 series high-performance embedded processor S3C2440 as the core to control the LCD touch screen , local area network, RS232 C interface , and simultaneously controls the analog input interface, digital state input interface and control output interface. The system composition principle block diagram is shown in Figure 1.

In order to reduce the interference of the transmitter to the controller, the analog input, digital state input and control output of the controller should be isolated. Among them, 16 analog inputs are selected by 16-to-1 analog switch (GPG control) to become one input, and then enter the ADC through isolation amplifier and signal conditioning. The ADC uses ADC channel 0 of ARM to input to ARM; 5 state inputs can enter ARM through GPIO (GPJ control) pin after photoelectric coupling isolation; and 6 control quantities are output through ARM's GPIO (GPJ control) and then drive solid-state relays after photoelectric coupling isolation .

2 Analog input and level normalization

The analog input channel of this controller is shown in Figure 2. Since the entire analog input channel works in DC coupling mode, special attention must be paid to the signal level and polarity of each level. The ADC uses the ADC embedded in S3C2440, with a resolution of 10 bits, a conversion rate of 500 ksps, an analog input range of 0 to 3.3 V, and 8 ADC channels.

This design uses channel 0, that is, AIN0 as the input channel. Because the analog input range is 0-3.3 V, and the analog input range is 0-5 V and 0.0I/0.1-1 V, the analog input level needs to be normalized to the analog input range of 0-3.3 V of the S3C2440 embedded ADC.

When the analog input range is 0 to 5 V, it is necessary to use an input amplifier to normalize them to 0 to 3.3 V. The design can be in the form of a common-mode amplifier and use a potentiometer to adjust the input voltage. When the input is 0 V, the output should also be 0 V; when the input is 5 V, the output should be 3.3 V. The reference circuit of the input amplifier is shown in Figure 3.

When the input range of the analog input is 0.01/0.1~1 V, the input signal needs to be amplified appropriately to obtain an output of 0~3.3 V. The input amplifier circuit at this time is shown in Figure 4.

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3 Digital signal channel design

The digital channel is the switch input and output channel of the controller. There are 5 types of input state signals and 6 types of output control signals. The digital input and output can be connected to the GPIO of ARM. In order to ensure a certain scalability, both the input state quantity and the output control quantity can be expanded to 8 bits, a total of 16 bits. This design only uses the lower 5 bits and the lower 6 bits as valid signal quantities, and the others are reserved for standby use.

3.1 Input state quantity interface circuit

The input state quantity can drive the buffer 74ABT541 after being isolated by the photoelectric coupler , and then connected to the GPIO of ARM. The circuit connection relationship is shown in Figure 5. Among them, the first five state quantities DT1 to DT8 input by the photoelectric coupler are valid state quantities, and the last three are reserved.

3.2 Output control quantity interface circuit

The GPIO output control quantity of the ARM processor is driven by the driver buffer 74ABT541 and then isolated by the photocoupler to drive the solid-state relay . Its circuit connection relationship is similar to Figure 5, but the direction is opposite. The control signals DK1~DK8 output by the photocoupler can drive 8 relays respectively. The first 6 are used according to the design requirements, and the last two are reserved (one is used for the buzzer ).

3.3 ARM GPIO allocation

ARM's GPIO allocation requires a total of 20 bits, including 8 bits for status input, 8 bits for control output, and 4 bits for analog switch channel selection, for a total of 20 IO pins.

The GPIO interface allocation can refer to the following principles: the relay control and analog switch control have a total of 12 bits, which can be used for GPJ0~12 ( digital camera interface); the input status quantity has a total of 8 bits, which can be used for GPF0~7 (interrupt EINT0~7). In addition, the GPG port can also be used.

3.4 ARM Processor

The core of the controller is the ARM processor, and related interfaces need to be expanded, such as LAN interface, RS232 interface, LCD interface (with touch function), USB interface (USB device, used to download programs), JTAG interface, etc. These are all standard interfaces of ARM. The circuit design can refer to the ARM utu2440 motherboard circuit for design, and this article will not introduce them one by one. Components can use the same model, but the corresponding industrial-grade chips should be selected . For example, if the network expansion chip utu2440 motherboard uses DM9000A (a commercial-grade chip), it should be replaced with DM9000BI.

4 Software Design

The control unit of the TV transmitter should display the working status of the monitoring of analog quantities such as the power amplifier voltage, current, incident power, transmission power, temperature, etc. through an extended LCD screen (with touch function). When faults such as overvoltage, overcurrent, overtemperature and excessive standing wave ratio occur, the control unit should have functions such as overload alarm, fault protection, fault reset, fault history recording and fault record clearing, and should also be equipped with a fault indicator light and an alarm buzzer.

The software working process of this system is to first select one signal from the 16 analog signals by controlling the ADG706 address selection, and then perform ADC sampling through AIN0, while monitoring whether the 16 analog signals have any faults. Read the corresponding status signal from the GPIO port to monitor whether the corresponding digital signal has any faults. If normal, it will be output to the display screen for display; if a fault occurs, a fault signal will be issued by controlling the output signal and driving the buzzer to alarm.

5 Conclusion

This paper introduces a design scheme of TV transmitter control unit based on Samsung's embedded processor S3C2440. This scheme monitors the working condition of TV transmitter by processing analog quantities such as power amplifier voltage, current, incident power, transmission power, temperature and some state quantities, and gives corresponding control signals. At present, this system has been successfully applied in practice. After practical verification, the functions of this system can meet actual needs.