The wireless receiving module (English name: RF Wireless Receiver Module) is generally divided into two types: super-regeneration and super-heterodyne receiving module. According to whether there is codec, it can be divided into wireless receiving head (without decoding, output pulse signal), wireless. Receiver board (with decoder chip, output TTL level signal). Wireless receiving module is widely used in wireless remote control, remote control toys, anti-theft alarm, garage door, rolling gate, gate, telescopic door and other door control industry, wireless 232 data communication, wireless 485/422 data communication, digital audio, digital image transmission In the field.
The module must be modulated with signals to work properly. Common fixed-code encoding devices such as PT2262/2272 can be connected as long as they are directly connected. It is very simple because it is a special encoding chip, so the effect is very good.
Another important use of the module is to use the microcontroller to achieve data communication. There are certain skills:
1, a reasonable communication rate
The maximum transmission data rate of the data module is 9.6KBs, which is generally controlled at about 2.5k. Excessive data rate will reduce the receiving sensitivity and increase the bit error rate or even work at all.
2. Reasonable information code format
When the MCU and the module work, they usually define the transmission protocol by themselves. Regardless of the modulation method used, the format of the information code to be transmitted is very important, which will directly affect the reliable transmission and reception of data.
Code group format recommendation
Preamble + sync code + data frame, the preamble length should be greater than 10ms to avoid background noise, because the first bit of data received by the receiving module is easily interfered (ie, zero-level interference) and the received data is caused. error. Therefore, using the CPU code can add some garbled code before the data identification bit to suppress zero-level interference. The sync code is mainly used to distinguish it from the preamble and data. There are certain characteristics, so that the software can identify the synchronization code through a certain algorithm and prepare for receiving data.
Data frames should not use non-return to zero code, but not longer 0 and longer 1. Manchester code or POCSAG code is used.3, the interference of the single chip to the receiving module
When the MCU simulates 2262, it is generally normal. However, when the MCU simulates 2272 decoding, it usually finds that the remote control distance is shortened a lot. This is because the multiplier of the clock frequency of the MCU will interfere with the receiving module. The electromagnetic interference of the 51 series MCU is relatively large, 2051 Slightly smaller, the PIC series is smaller, we need to use some anti-interference measures to reduce interference. For example, the single-chip microcomputer and the remote control receiving circuit are respectively powered by two 5 volt power sources, and the receiving board is separately powered by a 78L05. The clock area of the single chip microcomputer is far away from the receiving module, the working frequency of the single chip microcomputer is lowered, and the shielding is added in the middle.
It is better to make an isolation circuit when receiving the module and the 51 series MCU interface, which can better suppress the electromagnetic interference of the MCU to the receiving module.
When the receiving module works, it generally outputs a high-level pulse, which is not a DC level, so it cannot be tested with a multimeter. When debugging, an LED can be connected in series with a 3K resistor to monitor the output state of the module.
When the wireless data module and the dedicated codec chip such as PT2262/PT2272 are used, the connection is very simple. As long as it is directly connected, the transmission distance is ideal, generally up to 600 meters. If used with a single chip microcomputer or a microcomputer, it will be subjected to a single chip microcomputer or a microcomputer. The clock interference causes the transmission distance to drop significantly, and the general practical distance is within 200 meters.