Based on the current low stability and unreliable performance of the handheld touch screen, the AT91X40 series microcontroller is used as the control chip. Due to its powerful function, high integration, strong data processing capability and high stability, the AT91X40 series is based on the AT91X40 series. The hand-held touch screen is compact, powerful, and easy to operate. The display and input devices of the handheld touch screen use the ADS7843 and SED1335 two mainstream touch and LCD display chips. Through on-site experimental verification, the handheld touch screen based on AT91X40 series has high stability, reliable operation and practical application value.
Features of the touch control chip ADS7843
The ADS7843 is a 4-wire resistive touch screen conversion interface chip. It is a 12-bit sampling analog-to-digital converter with a synchronous serial interface. The power consumption is 750 μW at 125 kHz throughput rate and 2.7 V, and only 0.5 μW in shutdown mode. As a result, the ADS7843 is widely used in battery-powered small handheld devices due to its low power consumption and high speed. The ADS7843 is available in a SSOP-16 lead package with a temperature range of -40 to +85 °C. The ADS7843 has two auxiliary inputs (IN3, IN4) that can be set to 8-bit or 12-bit mode. The external connection circuit is shown in Figure 3. The operating voltage Vcc of this circuit is between 2.7 and 5.25 V, and the reference voltage is between 1 V and +Vcc. The circuit reference voltage determines the converter input range, and the analog voltage represented by each digital bit in the output data is equal to the reference voltage divided by 4,096. The average reference input current is determined by the ADS7843 conversion rate.
Figure 3 ADS7843 external connection circuit
Structure and characteristics of liquid crystal display chip SED1335
The liquid crystal display is referred to as LCD. Because of its low loss, low price, long life and convenient interface, the liquid crystal display is widely used in mobile phones, cameras, computers, smart instruments and other products. There are mainly two types of liquid crystal display controllers. One is to integrate the controller in the CPU to make a dedicated CPU with a liquid crystal display controller. This controller has a powerful CPU and a simple external circuit. It is generally only suitable for small-scale LCD modules. The other is a dedicated controller chip. This chip has a strong command function, simple interface with the CPU, easy to control, drive capability up to 640 & TImes; 256 dot matrix. The system's liquid crystal display control chip SED1335 has a powerful I/O buffer and a rich instruction system. It can transfer 4 bits of data in parallel, with a maximum drive capacity of 640 & TImes; 256 dot matrix, and can realize mixed display of graphic and text formats. Its structure includes an interface part, a management control part, and an LCD display driving part. The circuit principle is shown in Figure 4.
Figure 4 circuit schematic
Based on the AT91X40 series of handheld touch screens, it features compact size, powerful functions and easy operation. The display and input devices of the handheld touch screen use the popular touch screen. The touch screen technology has developed rapidly and has broad prospects. It has been widely used and has great research value. In this system, two mainstream touch and LCD display chips, ADS7843 and SED1335, are selected. The choice of the whole hardware highlights the mainstream and advanced nature, and guarantees that the research results have certain practical value.
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