rs485 arduino


. Today, you will learn about RS 485.. If you are familiar with RS 232, then you may already know a little bit about it., If not check out our other video. What is RS 232.? The link will be provided below. Before we get into todays video. If you love our videos, be sure to click the like button below and make sure to click subscribe and the bell to receive notifications of new RealPars videos.. This way you never miss another one. Just like its older brother, RS, 232 RS 485 is a form of serial communication., Think of RS 485 as the younger faster brother of RS232.. What made it such an advancement over RS 232 was the fact that it could transmit not only a single device to device transmission, but also a communications bus to connect multiple devices at once.. The configuration and specifications of RS 485 make it faster and extend the range of data transmission. You arent limited to fifty feet of cable like with RS 232.. The maximum cable length for RS 485 is typically listed as 1200 meters or about 4000 feet.. Much like RS, 232 RS 485 doesnt have an actual standard connector. Many times the old DB 9 connector is used. In some applications. Terminal strips were used in place of a connector.. This helped RS 485 become a widely used and very versatile form of serial communication.. Another advantage over RS 232 that I mentioned earlier is the number of connectable devices.

RS 485 can handle up to 32 connected devices. RS232 could only handle one.. This allowed users in manufacturing facilities to connect larger applications and whole machines with one protocol. Another plus for RS 485, is that it is less susceptible to noise. Issues.. Electric noise can cause all kinds of problems for electronics. RS 232 referenced ground to decipher the data. It was transmitting. This allowed for electrical noise to cause interference.. Rs 485 avoids this issue, which also allows for shielding of the cables to prevent noise.. You may be wondering what can I do with serial communications, especially RS 485.. One very common example in the automation world is remote control of VFDs or Variable Frequency. Drives. Many people just call them motor drives., A simple network of a PLC VFD and an HMI allows remote control of motors. In an industrial setting. Lets, say you were monitoring a water pump, filling a vessel.. You decide that the water is not filling fast enough to keep up with demand.. With your RS 485 network, you can remotely monitor and control that pump from a control center.. This is possible since the HMI is connected to your PLC via RS 485.. The PLC is also connected to the VFD via RS 485.. The PLC is programmed to monitor the level of the water in the vessel.. It also allows manual flow control if needed.. All of this allows you to speed up the VFD that controls the speed of that water pump.

Problem solved thanks to RS 485 communications. Let’s talk about what we now know about: RS 485.. It is faster and much more versatile than the older RS. 232. Users. Can utilize a longer cable up to 1200 meters or 4000 feet.? The greatest feature of RS 485 is the fact that you can connect up to 32 devices on one system.. Rs 232 could only handle one at a time.. There is no standard connector for the protocol.. Most manufacturers still utilize a DB 9 connector.. You can also still simply use a terminal strip.. This makes utilizing RS 485 simple.. All in all, RS 485 really allowed full automation possible with its ability to connect so many devices at once.. I truly hope this video was helpful.. Please dont forget to check back later for more RealPars videos, Make sure that you head over to To find even more training material for all of your PLC. Programing needs.. We offer many videos to assist you in learning PLC. Programing and landing that job in a high paying highly thought after field of automation and controls, engineering. Go to realpars.


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Comment (42)

  1. You forgot to mention that Interbus, DeviceNet, ProfiBus etc are all clones of RS485 with some extra features…

    1. lol, this is supposed to be an introductory video. You just can’t mention everything on the first go

  2. The RS485 is a comms that allows control of the IGBT however the VFD input output to the motor is a power system and this is not shown, there is a lot more going on.

    1. Correct. The purpose of this video is to demonstrate the ability of RS485 to communicate with a VFD. The power connections are not shown. RS485 can be used to send a start signal, a stop signal and a reference (setpoint) speed signal to a VFD that has an RS485 comm port. Other data, like motor status and speed can be sent back to the PLC from the VFD as well using RS485. Profibus is a more advanced protocol for communicating with VFD’s and other devices, but at its core, Profibus is based on RS485.

    2. @Scott Sommer I know all that it was confusing to see the line going to the motor in the same colour as the RS 485

  3. If RS-485 can handle up to 32 connected devices, why does the RS-485 port on the Easytouch automation system for a pool freak out when you connect 3 or more???

    1. Many consumer devices are capable of communications using modern protocols, but because they are limited in scope, the processors are not always set up to take full advantage of the power of those protocols. Many times, these consumer products, have artificial limits to their capabilities, such as 2 nodes on RW-485 or other limitations. They figure beyond the main controller, the user would only have two other nodes, such as an automatic chlorinator or a lighting controller. Even in an industrial system, a 32-node configuration would likely bring a controller to its knees from a timing and loading standpoint.

  4. can we interface RS485 and arduino. for eg:- here i have a sesnor which gives data through RS485 cable so can i interface it with arduino ?????

    1. Hey!

      Unfortunately, not at the moment. This is definitely a great topic suggestion, I have sent this over to our course developers.

      Thanks for sharing and happy learning!

    2. Happy to hear that! Welcome to the RealPars family! Feel free to leave all the questions you might have in our comment section.

      Just to let you know, that we also have a free course on PLC Hardware

    1. RTD’s are resistance devices. The wires that make up the RTD vary in resistance with change in temperature. Therefore, an RTD must be connected to an RTD I/O card in a PLC or DCS or be connected to a temperature transmitter. If the I/O rack is connected via RS-485 to the PLC, then you could connect an RTD to the I/O rack with the proper I/O card.

    1. You can use both in the same control system, but not on the same network. RS-232 is a point-to-point connection with a voltage signal. RS-485 is a multi-drop network which is current-based. I have used an RS-232 connection to connect a weigh scale to a PLC, and also have connected a gas chromatograph to the same PLC. In order to do that, I needed an interface card for RS-232 and a SEPARATE interface card for RS-485.

  5. RS485 is defunct in many newer systems, Bacnet MS/TP or Bacnet over IP is the way to go now… We used RS485 for many years, I hardly see it anymore.

    1. Hey!

      Thanks for your comment and feedback! I will make sure to pass this on to our creator team.

      Thanks for sharing!

      Happy learning!

  6. One doubt. In your example at the end, you used two RS485 cables. One to connect PLC to HMI and another one from PLC to VFD. But earlier you mentioned RS485 can connect to multiple terminals. If that’s the case, is it possible to use a single RS485 cable from PLC and a divider to divide the signal to VFD and HMI ?

    1. Up to 32
      transmitter/receiver pairs may be present on a RS485 network at one time. RS-485 is generally a 2-wire half-duplex system connected in a daisy-chained manner with single twisted pair cable. Many vendors also offer RS-485 multiplexers that allow for star configuration of the network.


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