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Because of this RS485 and the others can be used in situations with a severe ground level shift of several volts, where at the same time high bit rates are possible because the transition between logical 0 and logical 1 is only a few hundred millivolts. It is a method of transmitting data between two devices by sending it one bit at a time, sequentially, over a single wire or channel. RS485 employs a differential signaling scheme, transmitting data using two wires: one for the positive signal (A) and one for the negative signal (B). There are many standards in serial communication and RS485, also known as TIA-485 (-A) or EIA-485, is just one of them. I have various buttons, switches and LEDs on the physical unit that allow me to see if the sprinklers are running, the pump is running, the pool is filling or if there is a system error of some sort. The two-wire half-duplex system enables bidirectional data transmission between two devices, but not simultaneously. The fundamental operation of RS485 involves two wires, enabling half-duplex data transmission. I can run the Pi for about two hours or so on the small battery I have attached to the system and if the power does not come back on it time, then the MightyHat will automatically shutdown the Pi to prevent it from crashing due to a sudden power failure.

Every single circuit in my home is monitored by an electrical monitoring system. With this system I can monitor all of the electrical usage in my house and as part of the monitoring process, I store this data in a MySQL database. Over time I added in another piece to my pool control system. Now I can query the pump and control my pump adding in another capability that I did not have before. So once per minute I simply query my MySQL database and figure out how many watts are currently in use by my pool panel. Figure 1 shows an example of a correct Bus connection. Be sure to use a wire pair such as the blue and blue/white pair for the data lines and a third wire or pair twisted together for the common connection. For sensing I use a variety of sensors and methods of getting the information into a usable format. It stores this information in a MySQL database where I can then grab it for utilization in my pool control system.

That is why RS485 is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other. On my Raspberry Pi, I utilize a Low Power Labs MightyHat which provides UPS power backup to the Pi, an LCD status screen and intelligent power control for the Pi. I also have a momentary switch (second on the left) that allows me to manually fill my pool when I want, and finally on the left side I have a DPDT switch that physically interrupts power from my system to the sprinkler valve and triggers a GPIO event to tell the system we have manually disabled filling the pool. In addition to the system LEDs, I have a system ON/OFF button (top left) which allows me to use the MightyHat system to reboot or shutdown my Pi intelligently without having to login to the Pi to do it from the CLI. It has anti-ultraviolet and anti-rain features as well, making it suitable for long-term outdoor use. If distance between router and master inverter 80m, then use extender or repeater.

In fact, there is no such thing as an RS485 cable since RS485 is a protocol for serial communication (like between inverter and Zero export device) and Ethernet is a protocol for carrying internet data (between router and inverter) whereas CAT6 is a cable standard. Splicing of communications cable is not permitted. All communication cabling to be installed in a daisy chain configuration, what is rs485 cable no T’s are permitted. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. I installed them in a flow cell which also monitors if the pump is running. Above you can see where I toggle the pump running LED on and off when necessary. The ability to manage my Pentair variable speed pump. Russell's software allowed me to communicate directly with my pool pump via an RS485 interface. Enter Russell Goldin (tageyoureit) and his pool controller software project. The MightyHat is an Arduino clone so I used the Arduino IDE to program it to fit the needs of my project. Before digital instruments begin to operate, they must be set with measurement system parameters and communication parameters.