315M remote control transmitting and receiving circuit

Early transmitters mostly used LC oscillators, which had serious frequency drift. The emergence of SAW devices solved this problem. Their frequency stability is roughly the same as that of crystal oscillators, and their base frequency can reach hundreds of megahertz or even thousands of megahertz. No frequency multiplication is required, and the circuit is extremely simple compared to crystal oscillators. The following two circuits are common transmitter circuits. Due to the use of SAW devices, the circuits work very stably. Even if the antenna, SAW or other parts of the circuit are grasped by hand, the transmission frequency will not drift. Compared with Figure 1, the transmission power of Figure 2 is higher. It can reach more than 200 meters.

Figure 1

Figure II

The receiver can use super regenerative circuit or super heterodyne circuit. Super regenerative circuit has low cost and low power consumption of about 100uA. The sensitivity of a well-adjusted super regenerative circuit is similar to that of a super heterodyne receiver with one high-power amplifier, one oscillator, one mixer and two intermediate amplifiers. However, the working stability and selectivity of super regenerative circuit are relatively poor, which reduces the anti-interference ability. The figure below shows a typical super regenerative receiving circuit.

The sensitivity and selectivity of the superheterodyne circuit can be done very well. The monolithic integrated circuit launched by Micrel in the United States can complete reception and demodulation. Its MICRF002 is an improved version of MICRF001. Compared with MICRF001, it has lower power consumption and a power shutdown control terminal. MICRF002 has stable performance and is very easy to use. Compared with the super reproduction circuit, the disadvantage is that the cost is relatively high (RMB 35 yuan). The following is its pin arrangement and recommended circuit.

ICRF002 uses ceramic resonators. By changing to different resonators, the receiving frequency can cover 300-440MHz. MICRF002 has two working modes: scanning mode and fixed mode. The receiving bandwidth of scanning mode can reach hundreds of KHz. This mode is mainly used in conjunction with LC oscillator transmitters, because the frequency drift of LC transmitters is large. In scanning mode, the data communication rate is 2.5KBytes per second. The bandwidth of fixed mode is only tens of KHz. This mode is used to match transmitters that use crystal oscillator frequency stabilization, and the data rate can reach 10KBytes per second. The working mode selection is realized through the 16th pin (SWEN) of MICRF002. In addition, the wake-up function can be used to wake up the decoder or CPU to minimize power consumption.

MICRF002 is a complete single-chip superheterodyne receiving circuit, which basically realizes "direct data output" after "antenna input", and the receiving distance is generally 200 meters.