Introduction
Remote control equipment is very easy to see in daily life, home appliance remote control, toy remote control, etc., convenient for users to control equipment. For different needs, remote control equipment design is different, such as TV remote control without display, usually in infrared signal transmission; air conditioning remote control with display, common infrared (IR) and radio frequency (RF) transmission signal; High-end remote control products can update firmware through mobile phones, implement the version upgrade. This article describes a general solution for remote control equipment that supports LCD display; support infrared communication and expands RF communication method; user input adopts touch button implementation, fashion beauty; this program reserves NFC interface, expands NFC function; In terms of power management, support battery power, USB charging and wireless charging are convenient and practical.
1 Principle introduction
1.1 Capacitive Touch Button Principle
Touch button is getting more and more applications in electronic devices. Use the touch button to realize the human-machine interaction, microwave, refrigerator and other home appliances, etc., it is expected that there will be more and more touch buttons in the future replace the traditional mechanical buttons. The touch button has a strong durable, fast response speed, space, beautiful, easy to clean, and so many advantages. Touch button can be divided into four major categories, resistive, capacitive, infrared, and surface acoustic wave sensitive buttons. Among them, resistive, infrared and surface acoustic keys are mainly used in touch screens, rarely used in a single button. This program will focus on discussing the application of the capacitive touch button in a single button.
The capacitive touch button adopts the capacity of the determination standard. In the design of the touch button, it has some advantages, for example, directly integrated in the PCB, the touch sensing area has a flexible design, relatively low, and the like. In simple, the capacitive touch button changes the capacitance value when pressed, thereby changing the circuit oscillation cycle, and detects the detection of the button by changing the value of the oscillation cycle. 1 is a schematic diagram of a capacitive touch button principle.
Figure 1 Schematic diagram of the principle of touch button
In the no-load state, the induced area capacitor is determined by the material and structure (Fig. 1), the capacitance value is C1 + C2. The change capacitor is based on the parasitic effect, mainly consisting of parasitic capacitance between the external conductor and the PAD (Figure 1 Figure), the finger is pressed, the parasitic capacitance value changes, and the value value is C1 + C2 + C3 || C4. The capacitance access circuit constitutes an oscillator, and the change in the capacitance value causes the oscillation circuit output frequency change, and the trigger state of the button is determined by measuring the output frequency.
Button induction area design needs to avoid false triggering and taking care of sensitivity. In general, a single button induction area needs to be made enough to achieve the identification button purpose; the adjacent button induction area should be kept a certain distance, avoid malfunction; the touch sensing zone shape can be arbitrarily, a single button is circular, square Good.
TI's MSP430 supports a variety of touch implementations, reference documents [1].
1.2 Infrared Signal Transmission Principle
Infrared remote control principle can refer to the document [2]. This paper uses NEC protocol encoding, simply by means of time intervals between bursts to represent logic "0" and logic "1". The carrier signal frequency is 38K, and the logic "1" uses 0.56ms 38K carrier and 1.5 ms no carrier, the logic "0" uses 0.56ms carrier and 0.56ms no carrier, the frame head is added to the 9MS carrier plus 4.5 ms no Carrier is represented. Coded frame format Refer to Figure 2, the specific format definition can be modified in accordance with the actual situation.
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Figure 2 Infrared encoded data frame format
Ti's MSP430 Series MCU comes with Timer, which is convenient to generate a 38K carrier. The carrier when encoding has no control can be implemented by Timer's PWM output module [3]. Its PWM output module can be configured to have seven output modes that can be easily implemented. With the MSP430's Timer PWM output function, only one Timer and all the way PWM can easily implement infrared encoding, no additional hardware, software implementation is simple. Save the cost and development time for system design.
1.3 rechargeable touch screen remote control module design
The traditional remote control module is implemented by mechanical buttons. This solution uses a touch button design, buttons, and displayed on the same LCD screen, stylish, beautiful. This program is used as a reference design, except for the basic function of the remote control (button, display, transmitting, button), also designed charging and USB modules, and extended RF and NFC interfaces. The charging method improves flexibility, and the user only needs to charge without having to replace the battery. USB modules can communicate with PC-side application software. This plan is not only a remote control scheme, in other applications, this program also has a large reference value, and users only need to crop the function module of this program according to requirements. This scenario power module supports battery power supply and USB or DC adapter charging / power; touch buttons are implemented; RF and NFC modules use SPI and MCU interfaces; MSP430's own USB module can be convenient to PC-side application software interface, implementation Bidirectional communication of the PC and MCU. The system block diagram is shown in Figure 3.
Figure 3 system block diagram
2 design example
2.1 Hardware Design
2.1.1 Power Module Design
The system is powered, and the charging circuit is designed, USB or DC charging is supported. The power supply outputs 3.3V supply MCU after the LDO voltage regulation, ensuring the stability of the MCU operating voltage. Its circuit is implemented as shown in Figure 4 below.
Figure 4 Power Module Circuit Design
2.1.2 Design of LCD and Backlight Module
The MSP430F6638 comes with an LCD controller that can easily drive segment LCD screens. The screen backlight brightness is controlled by the Timer output PWM wave control, and the adjustment is convenient. The backlight circuit is shown in Figure 5. By changing the frequency and duty cycle of the PWM, the backlight brightness can be changed to change the LCD screen view.
Figure 5 Backlight circuit design
2.1.3 Touch button design
The MSP430F6638 comes with comparator B. You can support up to 12 touch buttons. The output of comparator B is connected to the CLK input of Timer. When the finger presses, the touch sensing zone capacitance value changes, the comparator flip cycle grows long, compare The server outputs a count pulse as Timer, which is smaller in the fixed time, and determines the key operation based on the change in the Timer count value in the fixed time. Touch button detection can be implemented by appropriate configuration registers and software algorithms. The circuit design is shown in Figure 6. Note that in order to reduce noise, each channel external resistance should not be too small, optional 500K. The comparator B-turn level is implemented by the configuration register, please refer to the manual [3].
Figure 6 Touch button circuit design
2.1.4 Infrared emission module design
The infrared module is implemented in conventional infrared pipes and implements infrared encoding by configuring the appropriate PWM wave by configuring TIMER. The infrared emission instantaneous current is large, and the infrared emission lamp is driven by the GPIO control of the MCU to improve the emission current. The infrared emission module needs to cooperate with the receiving module to communicate in the same encoding format. The infrared module circuit diagram is shown in Figure 7.
Figure 7 Infrared emission module
2.1.5 USB module design
The MSP430F6638 comes with a USB module that implements USB communication with simple hardware design. This article uses USB virtual UART implementation and PC communication. For USB debugging, please refer to Ti official website information [4].
2.2 software design
2.2.1 Embedded Software Design
The system software flow is shown in Figure 8. When there is no button action, the system runs RTC, showing the current time, temperature, and transmits the time, temperature, and button status (no all button actions) information to the PC. When the button is pressed, in addition to the above functions, the system will also perform the upper layer logic, such as whether the time setting mode is entered, whether the buzzer and which infrared code, etc.
Figure 8 Software flow chart
2.2.2 PC end software design
In order to facilitate human-operated interaction, a matching PC-side software implementation and two-way communication of MCU are developed using C Sharp language. The current state of DEMO can be viewed by the PC side software, including time, temperature, buttons, etc., and can also change the brightness of the DEMO backlight by the PC side. The PC side software is shown in Figure 9.
Figure 9 PC end software
Demo is connected to the PC-port COM port via the USB cable, and the USB of the MSP430F6638 passes the software protocol virtual UART, selecting the appropriate COM port number in the PC side to implement the interconnection of PC software and DEMO. The left diagram in Figure 9 reflects the real thing of Demo. When the button is pressed, the corresponding button icon flashes, and the text recorded this action (Button XX PRESSED!). The lowermost chart displays the current temperature information in real time.
2.3 Demo display
Demo is shown in Figure 10. 12 buttons, each button, press the icon to flash, and the buzzer is about 0.3 s. Each button has different functions, which can transmit different infrared code to the function of the remote control according to the requirements. Demonstrate Demo Middle Code supports RTC and thermometer functions, support flexible adjustment time, while adjusting the screen backlight through the PC side software. Demo also expands the light sensing module, which can adjust the backlight brightness based on the environmental light, achieve better visual effects.
NFC interface transponder
Touch screen technology
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