Data transmission modulator/demodulator composed of SST8803 and UM3758-108A

The main component of this circuit is the new power grid carrier digital pulse signal transmission modulation/demodulation integrated circuit SST8803, which has the characteristics of low power consumption, high sensitivity, good anti-interference and anti-static performance, etc. A single chip can complete all the work of data signal modulation, transmission, reception and demodulation. It can use low-voltage power lines, broadcasting lines and closed-circuit television signal lines as carriers for data information exchange, and can be used for remote control and telemetry, centralized alarm, multi-channel paging and microcomputer network systems.

Figure (a) is a typical application circuit of SST8803. Pins ⑩ and ⑥ of ICl are positive and negative power supply terminals, and the minimum voltage limit is -0.3V and the maximum is 6.5V. Pin ⑧ is the reference voltage output terminal, VREF=VDD/2, and C11 is connected to pin 9 as a filter capacitor. The internal circuit of pins 11 and 12 and the quartz crystal X1 generate a 455kHz clock signal for signal modulation or demodulation. Pin 15 is the working mode selection terminal. When the low level is applied, it is in the modulation and transmission state, and when the high level is applied, it is in the receiving and demodulation state, which can easily realize half-duplex communication. R7, C7, and VD2 form an automatic reset circuit. VDl is a 6.5V voltage limiting protection tube, which ensures that the circuit is not damaged when the power grid generates transient pulse high voltage.

Figure (b) is an example of SST8803 connected to a digital encoder/decoder. IC2 is a digital signal encoding and decoding compatible device UM3758-108A, whose clock frequency f=l/0.5Rs・Cs, and this circuit uses f=160kHz. IC2①~⑩pins are three-state address code input terminals, and the maximum address code capacity is 310=59049. IC211~18pins are data input (encoding)/output (decoding) terminals, which is an 8-bit parallel port. S1 is the working mode selection switch. When encoding, the 21st pin of IC2 is high level. After being inverted by the inverter IC3-1 of CD4069, the 15th pin of IC1 is low level (modulation state). The coded data stream is serially output from the 23rd pin of IC2 to the 5th pin of IC1, and sent to the power grid after modulation. When decoding, the 21st pin of IC2 is low level, and the 15th pin of IC1 is high level (demodulation state). The demodulated digital signal is sent from the 17th pin of IC1 to the 22nd pin of IC2, and is output from the 11th to 18th pin of IC2 after decoding. At this time, the 1st pin of IC2 is connected to the light-emitting diode LED1. If the input signal is valid, the 23rd pin of IC2 outputs a low level signal, driving the LED1 to flash, as a sign of successful reception and decoding.