There are many different types of serial communication protocols like I2C and SPI which can be easily implemented with Arduino and today we are going to look at another most commonly used protocol called RS485 which is very commonly used in high noise industrial environments to transfer the data over a long distance. It does not specify or recommend any communications protocol; Other standards define the protocols for communication over an RS-485 link. The below image shows the transmitter and receiver circuit diagram for Arduino's long-distance wired communication. The connection diagram for the above circuit is also given below. The circuit diagram given above explains how the onboard MAX485 IC is connected to various components and provide 0.1-inch standard spacing headers to be used with breadboard if you like. It also has onboard LEDs to display the current state of the chip i.e. whether the chip is powered or its transmitting or receiving data making it easier to debug and use. RS232 uses inverse logic; that is, a positive bit at the HCS12 UART is inverted by the onboard RS232 driver chip and appears as a negative signal on the serial cable. Most computers conform to IBM PC AT-compatible RS232 interfaces which use 9-pin D-Type connectors, consequently the PDQ Board brings out its serial ports to two female 9-pin D-Type connectors on the Docking Panel.

They are often terminated with 8 pin RJ45 connectors at either end. There are many categories of Ethernet cables we can use like CAT-4, CAT-5, CAT-5E, CAT-6, CAT-6A, etc. In our tutorial, we are going to use CAT-6E cable which has 4 twisted pairs of 24AWG wires and can support up to 600MHz. It is terminated at both ends by an RJ45 connector. 2 Alphanumeric LCD, and MAX485 UART to RS485 converter IC connected to each end of an Ethernet Cat-6E cable via an RJ45 connector. This UART-RS485 Converter module has an on-board MAX485 chip which is a low-power and slew-rate-limited transceiver used for RS-485 communication. In this tutorial, we are going to learn about the RS485 communication protocol and how to implement it with the two Arduino Nano we have with us and how to use the MAX485 RS485 to UART conversion Module. It works on half-duplex communication to implement the function of converting the TTL level into RS-485 level which means it can either transmit or receive at any time, not both, it can achieve a maximum transmission rate of 2.5Mbps. MAX485 transceiver draws a supply current of between 120μA and 500μA under the unloaded or fully loaded conditions when the driver is disabled.

At 1200m of transmission speed, you can use only 100kbps of transmission speed. Sig- lines are twisted as twisting nullify the effect of electromagnetic noise induced in a cable and provide a much better immunity against the noise which allows the RS485 to transmit the data up to 1200m of range. Failure to stay within this range will result in, at best, signal corruption, and, at worst, damage to connected devices. We will send some data from the transmitter side over the cable from the Nano which is converted to RS485 signals via MAX RS485 Module working in Master Mode. Do note that both transmitter and receiver circuits look identical the only thing that differs is the code written into it. This connection may be used to limit the common-mode signal that can be impressed on the receiver inputs. Normally, this connection is made at one end of the main cable.

In either of these cases, a source of noise that caused one bit to be received incorrectly would invalidate the received byte, since the total number of '1' bits would be odd rather than even. It is very well documented and widely used and it also has a parity bit to allow for error checking. If SPIF is set, reading the received data or initiating a new data transfer automatically clears the SPIF bit. When we think of long-distance data transfer, we instantly think about connecting to the internet via Ethernet cables. By connecting pairs of these handshaking signals together, the terminal or PC can be made to think that the QScreen Controller is always ready to send and receive data. After connecting as for point B, in the Settings it is possible to define a name for the device, and if the reading periodicity is less than 250 minutes, you can set an interval of hours in which the reading is not carried out / transmitted (for example you can disable the night). Twisted pair also allows the transmission speeds to be much higher than what is possible with straight cables.

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