What is interesting about PowerLine? No additional wiring is required. Most of the devices in the modern world are powered by external sources by wires. Radio modules in their mass are no exception. Power can be either a constant current of 12-24V or alternating current of 110V — 220V. To transmit information it does not matter if there is voltage in the line or not, you need only two wires. This technology does not take radio frequency, does not require the laying of additional wires. It uses existing power wires. The prototypes of the modem were made, tests were carried out, the electric circuit schemes were developed. A modem is a device that modulates the UART signal with a radio frequency. The signal modulation method is CW, the frequency is 1.87 MHz (160 m). The UART speed is 1200-19200 bps. This modem makes it very easy to combine various devices based on Arduino. You can connect this board to Raspberry PI. Control the PLC through UART text mode.
DetailsBecause our modem is most likely to work in an environment with other modems, e.g., modems G3 Prime, HomePlug, then the task is to filter out frequencies not included in the frequency range we used when receiving the signal.
With galvanic isolation everything is clear, why the bandpass filter? If you look at the circuit, it's just a high-pass filter, but ... As a high-pass filter, the filter is designed for a cut-off frequency of 1.7 MHz (at low frequencies). Those. All that is lower, including a 50-60 Hz network is not visible in principle. The resonance frequency of the oscillatory circuit is approximately 2.5-3 MHz. The ferrite is selected for which the operating frequency is approximately 1 MHz. Thus, the "physics" of ferrite works as a low-pass filter. As a result, the frequencies of modem bypassed is 1.8 - 1.9 MHz. All that's lower and higher is cut. Our required frequency is 1.87 MHz. At the resonance frequency, the amplitude amplification (simulation) is approximately 100-120 times. But taking into account the physical limitations of ferrite, the real resonance was obtained at the frequencies 1.8 - 1.9 MHz, and is approximately 15-30 times in amplitude. This is what we need.
Implementation in the HWA specialized board is developed as Arduino shield - the PLC modem.
InterfacesIn Arduino you can use one from:
- SPI
- I2C
- UART
Detail description how it work: http://open-plc.blogspot.ru/2017/02/plc-modem.html.
Features of Modem- Operating range of supply voltage DC 0-48V, AC 0-250V
- The maximum power consumption does not exceed 1W
- Modem operation mode continuous; transparent
- Connectors Arduino UNO compatible
- Used interfaces One from SPI; I2C; UART
- Logical organization of networks
- Simple peer-to-peer networks without the possibility of subnetting, each modem has a unique address
- Data transfer rate on the PLC network 1200 - 19200 bps
- Frequency range for data transfer via PLC
- Fixed, 1.87 MHz level of signal less than 116 dBmV
The first implementation "in hardware" will be both a shield and a library for Arduino. At the moment, it is in development and testing.
In the same project, the modem is implemented as a plug-in socket with analysis of power consumption and load dimming.
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