1 Introduction This paper will introduce the new design and application development of the car wireless Remote Control door opening system. A typical wireless remote door opening system - the remote key (RKE) system used in automotive safety applications, is shown in Figure 1. The system consists of a controller (or receiver) mounted on the car and a transceiver (or transmitter) carried by the user, ie a wireless remote control door key. The transceiver typically includes a microcontroller, RF device, and human interface devices such as buttons and LEDs. The microcontroller can be used with the DS89C440 or PIC16F639, and the RF device can be used with the MAX7044 or MAX1479 or TRF6901. The transceiver is normally turned off and only works when a button is pressed or when data needs to be sent. The transceiver is used to send data to the controller and is therefore one-way communication. However, this situation is changing. The new smart transceiver can send data as well as receive data, so it is two-way communication. In a two-way communication system, the controller (mounted on the car) and the transceiver (ie the car key) enable automatic communication without the need for a human-machine interface. 2 design ideas It can be seen from the above-mentioned wireless remote control door opening system that the design concept of the system solution is based on constructing a transmitter (remote key) and a receiver with a microcontroller. The MAXQ family is known to be a 16-bit RISC microcontroller optimized for low-noise design and optimized for analog circuit operation, and can be integrated with RF receiver devices to create the best solution for analog circuits. 2.1 Remote control key (transmitter or transceiver) and receiver (on-board controller) The remote control key can be configured with the DS89C450-KIT and MAX7044 or two evaluation boards (EV KIT), the DS89C450-KIT and the MAX7044EVKIT (EVht). It can be mounted in a housing with the rechargeable battery located below. If an antenna is used, the transmission distance is several orders of magnitude beyond the standard keychain. The receiver (on-board controller) consists of a MAXQ3212 16-bit microcontroller and a MAXl473 receiver mounted side-by-side. The connection is connected to the car's body control module (BCM). For debugging or demonstration, a dedicated MAXQ3212 port pin can be used to send asynchronous serial data at 9600 bps. The reason why the MAXQ3212 16-bit microcontroller is used here is because the MAXQ series is a 16-bit RISC microcontroller optimized for low-noise design and optimized for analog circuit operation. In addition to digital components, it also integrates high-precision simulation. The function, thus the application requires fewer chips, can be integrated with the RF receiver device MAXl473 to build the best solution for the analog circuit, and does not interfere with the RF signal. Its superior power consumption and powerful combination of features make product design and build easier and reduce time-to-market. The RF receiver device MAXl473 is the latest 300MHz to 450MHz ASK (Amplitude Modulated Modulation) RF receiver with an average sensitivity of -114dBm, which consumes only 5.5mA (typ) of normal operation. Built-in image rejection, eliminating the need for a front-end SAW filter. In sleep mode, the MAXl473 can start and send data in less than 250ps, ensuring a deeper sleep cycle and longer battery life. The MAXl473 operates from a 3V to 5V supply voltage. The 300MHz to 450MHz transmitter and receiver have the greatest advantage of doubling the effective range of the RKE system, ideal for sub-battery-powered devices including key, car alarm and tire pressure detection. 2.2 About analog signal strength measurement The MAXl473 receiver provides an analog received signal strength indicator (RSS1) that can be measured. The MAXQ3212 includes an analog comparator to compare the VREF and CMPI inputs and generate a pulse width modulated signal (PWM) on the timer output pin. Figure 2 shows the method of constructing an ADC from a comparator and PWM. Send the RSSI signal to the VREF pin of the MAXQ3212 comparator. The timer is then programmed to PWM mode. If the PWM is properly filtered, the DAC output is generated to the T2PB pin and the output (ie, DAC) is connected to the other input CMPI pin of the comparator. The comparator then compares the signal levels and if the signals match, the analog to digital conversion can be successfully performed without a dedicated hardware ADC. The software does not use the successive approximation method, but uses a slope ADC. Starting from a reasonable minimum, the DAC output slowly increases until the comparator indicates a match. 2.3 How to decode RF signals The MAXl473 receiver provides a digital signal output (DATAOUT). Since RF noise is always present, the pin will continuously transition state regardless of whether the keychain is actually transmitting data. To distinguish this noise from the signal, the MAXQ microcontroller must use a small software state machine to measure the time between the rising and falling edge signals to identify the preamble. The most efficient way to measure the edge interval is to use the interrupt trigger technique. MAXQ can be programmed to trigger an interrupt on either a rising or falling edge. Set the interrupt to the "rising edge" trigger, which starts the measurement. Once a rising edge is detected, the timer is reset and restarted, and the interrupt trigger edge is set to the "falling" edge. The interrupt handler reads the value of the timer on the falling edge. This can be done with a short program to show a code segment that reads and resets the timer and then converts the polarity of the interrupt trigger signal. If the edge interval matches the 8400 bps data rate (plus/minus a reasonable tolerance) and the number of sync pulses specified by the protocol is detected, the microcontroller software state machine switches to receive mode and begins parsing the remaining packets. 2.4 About data flow - the use of Manchester coding The protocol of the transmitter (remote key) data stream (burst) shown in Figure 1 varies greatly depending on the manufacturer, model, and factory time. For this aftermarket project, using a programmable microcontroller is just right. The 8400bps Manchester-encoded digital data stream is randomly selected and transmitted at 433MHz using ASK (Amplitude Transform Modulation). To use FSK (Frequency Modulation Modulation) or a different transmit frequency, the MAXl473 must be replaced with a different receiver chip. (1) The basic concept of Manchester coding Each data bit is represented by at least one signal transition, thereby enabling self-synchronization of the data stream. Figure 3(a) shows the representation of 0 and 1, where the falling edge is chosen to be 0 and the rising edge is 1. String data is usually sent first in the LSB. As shown in Fig. 3(b), the ASCII character "A" (41h, 0100.000 lb) is transmitted in the form of 1000.0010b. The coding can be formed by connecting the symbols of 0 and 1. Figure 3(b) forms the encoding of ASCII "A" by connecting the symbols of 0 and 1. (2) Data flow and software When the button on the key fob is pressed, the preamble will be sent, followed by the ID, count value and key data, as shown in Figure 4. The transmitter repeats the sequence until the button is released, and a software debouncer is required. In this example code, this is done simply by briefly closing the receiver. The actual system will also encrypt some of the data to prevent theft of the vehicle. It is generally decrypted by the vehicle body control module (BCM). The receiver software measures the received signal strength, waits and synchronizes to the preamble, decodes the data stream, and transmits the data over the serial port. Our company is specialized in supplying high quality Filter Drier,including A/C filter,accumulator,filter with nuts,two inlets and one outlet filter drier,filter drier with capillary,filter drier with Access Valve,filter drier with tube,multi copper filter drier,multi filter with capillary,filter drier with sight glass.The structure and dimension of each filter drier is customizable, ensuring customers are getting the right fitting for their needs.Our parts have been exported to over 50 countries all over the world. Filter Drier Filter Drier,Copper Filter Drier With Access Valve,Copper Filter Drier For Refrigerator ZHEJIANG ICE LOONG ENVIRONMENTAL SCI-TECH CO.,LTD. , https://www.china-refrigerantgas.com
