Keyless multifunctional TV remote control based on micromachined accelerometer

1 Introduction
With the rapid development of science and technology, people's daily necessities are constantly developing in the direction of easy operation, easy portability and intelligence. As an important daily necessity, the remote control of TV is easy to operate, keyless and intelligent, which is the current development trend. With the increasing maturity of micromechanical accelerometer technology, its miniaturization, low power consumption, high precision, intelligence and low cost make the application of TV remote control possible.

This design uses the characteristics of the single-chip microcomputer, such as small size, rich functions, high precision, and convenient and fast online simulation, to achieve simple and convenient control of the TV. This design adopts a completely keyless design model and uses an accelerometer to accurately determine the control direction. This remote control has four directions in two dimensions, namely four function keys. According to practical analysis, the four keys can meet the basic operation of the TV. Under normal conditions, the X-axis direction is used for volume adjustment and the Y-axis direction is used for channel adjustment. The system is powered by a battery pack and uses universal coding for TV remote control. It is practical and convenient, suitable for the operation methods and habits of different groups of people in society. Its simple and low power consumption characteristics are the direction of future TV remote control development. The innovation of this design: realize keyless control system, use the direction quantity and size of the micromechanical accelerometer on all vectors to achieve remote control; the circuit design is unique, which fully meets the design characteristics of accelerometer performance; the product is small in size, battery-powered, and has strong flexibility in appearance design. Different degrees of changes to it can be applied to different occasions and different groups of people; the error elimination and algorithm measurement of the accelerometer are realized through software.

2 System Structure
The whole system mainly includes three parts: signal acquisition, processing, and transmission. The design of each module directly affects the realization of system functions. The analog signal output by the general accelerometer is relatively weak. Due to the influence of internal and external interference in the system, the measured signal is mixed with interference signals. When the measured signal is very weak, it will be "swamped" by the interference noise, resulting in a large data acquisition error. Therefore, the signal must be filtered before amplification. Amplify the signal to an appropriate range to obtain the highest possible resolution. In addition, the module should be as close to the signal source as possible, so that the signal is amplified before being affected by the environment, so that the signal-to-noise ratio can be improved. The LM358 filter amplifier circuit is selected here. The amplified analog signal is then transmitted to the A/D converter and converted into a digital signal. Since the microcontroller has an A/D conversion function inside, the entire conversion process is implemented inside the microcontroller without adding an additional A/D converter. At the same time, the microcontroller is used to analyze and process the signal; then the signal is transmitted through the RF transceiver module. The system block diagram is shown in Figure 1.

3 Hardware Circuit Design
The hardware of the keyless multifunctional TV remote control mainly includes three parts: accelerometer sensor unit, controller unit and infrared transmitter unit.
3.1 Accelerometer sensor unit
The principle block diagram of the accelerometer sensor unit is shown in Figure 2. The three-axis accelerometer ADXL330 is selected. This device can simultaneously measure gravity acceleration in three different directions. The system only uses two output signals, namely the X-axis and Y-axis directions.

3.2 Controller unit
Figure 3 is a block diagram of the controller unit. The controller's P30/AN00 and P31/AN01 pins receive the amplified sensor acquisition signal. The P60~P67 and P00~P07 pins are connected to the transmitter to send the transmission code. The MOD pin is connected to an external jumper to select the corresponding voltage in the working mode or download and burn mode. The RST reset pin is connected to an external button for system reset.

3.3 Infrared transmitter unit
The infrared transmitter unit uses MC50462AP, which is powered by 5 V (AVDD) and transmits the remote control code through the infrared diode port.

4 Software Design
After the microcontroller is powered on and reset, it first determines whether there is an analog signal input to the input port. If not, it repeats the detection and judgment. If yes, it loops the acquisition of the port signal. After acquisition, the acquired signal is converted into A/D in the microcontroller, and the converted digital signal is calibrated. Due to various reasons, the input acceleration signal cannot be in a single direction. Therefore, it is simplified and assumed that the input signal is always in a single direction. If inputs are detected in multiple directions at the same time, each input will be compared, and then a maximum value will be selected as its only input. Finally, by analyzing the input, the processing subroutines of each input are designed and their functions are set.

Since the three-axis accelerometer can output acceleration values ​​in three different directions, different functions can be set for different inputs. Each input corresponds to a function and is reflected through its own subroutine. Figure 4 shows the software design process.

Since the system is powered by batteries, the system is in a dormant state when there is no signal input, and is in a working state only when there is a signal input. After starting or resetting for 5 s, if there is no signal input, it enters a dormant state to reduce power consumption.
Through experiments, it is verified that the average minimum acceleration of the artificial swing remote control is 1 g, that is, the calibration value set by the system is 1 g. If the acceleration is less than 1 g, it is considered an invalid signal. In this system, there is no need to consider the elimination of input jitter in particular, and the jitter can be completely treated as an input signal. The signal transmission completely adopts the transmission principle of the universal TV remote control. The oscillator inside the microprocessor chip and the external oscillation crystal form a high-frequency oscillator to generate a high-frequency oscillation signal. This signal is sent to the timing signal generator to generate a sine signal and a timing pulse signal. The sine signal is sent to the coding modulator as a carrier signal; the timing pulse signal is sent to the command encoder as a modulation signal to be sent, and then modulated in the modulator and sent to the infrared light-emitting diode VD to transmit the pulse modulation signal.

5 Conclusion
This paper introduces the design of a keyless remote control based on micromechanical accelerometer. This product can control the TV by using motion posture. It is simple and convenient to operate and is especially suitable for people with limited mobility. It also has strong expansion functions and can control the posture of toy cars and electric toys and control the production machine tools in the workshop. Due to the small size, low power consumption and low cost of micro-accelerometers, similar devices have a wide market.