Questions tagged [rs485]

EIA RS-485 is a serial communication standard using differential signaling.

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RS485 bus with an Ethernet cable

I need to connect some fan coil to a Raspberry PI, using Modbus with a RS485 serial bus. In my electrical wiring I already have a corrugated conduit for each fan coil, to connect them to the electric ...
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107 views

Number of bits after stop bit before going to idle state. Is it regulated by a industrial standard?

Does anyone know a number of bits after stop bit before going to idle state. Is there any standard on this matter (e.g. industrial)? Update: So my questions are: What marked areas stand for. What ...
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26 views

Cannot use SoftwareSerial and RS485 protocol in the same code

Could someone help me ? I want to make 5 nanos communicating through RS485 protocol with my Arduino Uno master. This part is working great by using the code of http://www.gammon.com.au/forum/?id=...
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40 views

PIC18F26J50 serial communications over RS485 link

I'm trying to figure out why my serial communication is not working. The design is to use the UART of a PIC18F26J50 over a RS485 link. Here is the relevant part of the schematic. Other relevant info:...
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39 views

SPI with differential line drivers, and star configuration problem

Folks I am helping to design a circuit for a group that uses the odrive motor driver board. The odrive drives two brushless motors and the MCU uses SPI to connect to motor encoders. People using the ...
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62 views

Electronically verify whether cable is connected to RJ45 connector

Background: I have a device that interfaces with a motor controller over RS-485 via an RJ45 socket. Currently, the port is a standard 4x2 RJ45 connector with the RS-485 using pins 2 and 7 ...
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1answer
40 views

how will a connector affect a transmission line?

I am laying out an RS485 driver and read a few design guides which recommend a 120 Ohm termination resistor. This makes sense since the characteristic impedance of twisted pair cables is in the 100 ...
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42 views

Long-Distance Multi-Slave Communication

I am currently trying to connect many serial slave devices to my Arduino device over a 14 meter distance. I am looking to have slave-to-master communication. These devices include: 3 BME280 ...
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27 views

RFI protection for a stepper motor controller

I'm building a remote tuning device for a magnetic loop antenna. It will use a stepper motor to turn the shaft on the mag loop's variable capacitor. The electronics will consist primarily of a ...
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79 views

RS485 PCB Design

I'm currently in the process of designing PCBs for my project. There's going to be one larger control board, and 10 daughter boards. The daughter boards will measure the current/voltage of some ...
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1answer
66 views

Communication between device for 5 meters and low speeds

I need to make a communication between only two devices with a distance of 5 meters, which are connected by a cable of 4x2.5mm² (see in the image), being 1 wire for GND and wire for 12v, that would ...
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2answers
51 views

How VFD affects an isolated IOT system

To avoid noise from the external system I tried to isolate the internal completely. So I added DC-DC isolated converter with signal isolation. I have attached the picture. Still when reading data and ...
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116 views

Implementing Modbus RTU on a UART device

I have a particle counter HPMA115S0 which has a UART communication interface. I bought a TTL UART to RS485 Converter Module to make it work with a PLC over Modbus RTU protocol. I usually work with ...
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64 views

MAX485 controlling output voltage

I'm trying to use a MAX485 module to interface a RS-485 domotic bus, when I use the oscilloscope I see that the original bus signals (A and B) are between 1.9 V high and -2.250 V low (4.15 V amplitude,...
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30 views

Implications of using a 2C-#18 twisted shield pair nec type cmr cable for RS-485

The cable will be passing modbus and another equal cable will be used for loadshare. The total cable distance will be about 100ft. Its catalog number E2032S. I notice other threads related to CAT5, ...
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104 views

Switching of RS485 differential line. Two sources, one output

I'm looking for a solution for my project. I have two signal sources (primary source and secondary source) on the RS485 (A/B) differential line. When/if something goes wrong on the primary, then I ...
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59 views

RS422/RS485 data input series resistor

I am using an RS422/RS485 driver to send Arduino 5V logic data over longer distances. I use the SN75174 driver for this purpose. In order to avoid ringing, I am not sure if I have to connect a series ...
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1answer
164 views

Reverse-engineering RS-485 communication

I've been trying to reverse engineer the communications protocol used by my home domotics, which I was able to determine uses a RS-485 implementation. I'm using a USB RS-485 serial dongle and an ...
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1answer
61 views

RS485 full duplex to Adapter with A and B ports

I need to configure a sensor (Thies 3D Sonic Anemometer, Manual: https://www.biral.com/wp-content/uploads/2015/01/4.383x.xx_.xxxUS3D.pdf) via my computer, it has RS485 full duplex and half-duplex ...
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1answer
53 views

Relay+SMPS = Noise in RS-485 bus

I designed a board with a microcontroller (Atmega328), 3 relays and a RS485 transceiver. The relays control SMPS LED drivers (Meanwell LPF series). The system consists of 10 boards, each one ...
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1answer
48 views

J1708 (open collector RS485) at higher baud rates than 9600 bps?

I have here a PCB which has a kind of "open collector" RS-485, known as J1708 (schematic attached). The default baud rate is 9600 bps and there is no terminators, J1708-TX is a 3.3V signal. I would ...
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45 views

RE: Receiver Output Enable and DE: Driver Output Enable pins

Hello I am planning to use LT1785 UART-RS484 transceiver. I will use that chip in order to get RS485 data and convert it to UART signal. So I have read the datasheet but I couldn't be sure. It says ...
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2answers
93 views

Rs485 to UART convension

I need to send data from one PIC to another PIC by using RS485. As a protocol I use UART. However, I cannot be sure about RS485 transceiver and its circuit. I will be able to supply 5 V and according ...
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53 views

Transmission distance rs485 vs ethernet

I have a question, why is rs485 limited to less than 100 meters at 10mpbs ( mbaud ) and is 100Base-TX ethernet applicable on 100 meters with 100 mbps bitrate i know that rs485 normally use a sort ...
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623 views

Effect of “wrong” driver with slightly long RS-485 stubs

I have a planned 250 kbit/sec, single-pair, 36-metre RS-485 installation where it is advantageous for wiring purposes if the stub lengths can be a little longer than optimal. There is a single almost-...
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43 views

RPi USB to Serial testing

I have a system like this: RPi -> FTDI(USB UART IC) -> RS485 transceiver -> RS485 TO USB board -> PC I'm having some trouble testing RS485 communication between the RPi and the PC. I'm using a simple ...
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1answer
800 views

RS-485 using USART or UART port on STM32

On STM32F405 MCUs there are USART ports as well as UART ports available. If I need to implement RS-485 communication then which one of these should be used, USART or UART? Or are both of them equally ...
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1answer
27 views

SN65HVD3x (RS485 Driver) - Termination resistor

I want to use the SN65HVD31DR to connect two microcontrollers together. The connecting cable has an impedance of Z0 = 80Ω. According to the data sheet it is recommended to terminate the connection ...
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1answer
53 views

How do you monitor communications on a positive-grounded device from a negative-grounded desktop?

I have a need to read the signals being sent between two boards in a lighting fixture. In preparing to do this I have read much about the chips, RS485, and analysers/decoders that are out there. I am ...
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2answers
117 views

RS485 vs RS232 similarity vs differences

I have used UART RS232 communication between MCUs extensively. Now I need to interface my STM32F407 MCU over RS485 bus with with devices. I have understood few things about RS485 but not-clear about ...
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2answers
86 views

Medium Range Two Wire Bus Recommendations?

Do you have any recommendations for a medium range (~10 meters) two-wire bus? My supply voltage is 24V and I'll have a single master with ~50 slaves connected to it. I've looked into: I2C - Great but ...
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25 views

Signal Attenuation TVS and series resistor

This question is in regards to signal attenuation on high speed data lines like RS-485 (and any others as well). I'm new to the signal world, so please bear with me here. Are there some useful ...
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1answer
51 views

RS485 Rx signal connected with two drivers

I wonder why is RS485_Rx is connected with two line drivers while RS485_Tx is connected with only one line driver. Is this some mistake in the schematics or is it some standard circuit for RS485?
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154 views

Multiple MAX3485 on same UART

I am working on a project where I have 4 MAX3485 (for 4 different RS-485 channels) chips talking on the same UART bus with an ESP-WROOM32 module. This is the schematic: simulate this circuit – ...
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76 views

How to select the most appropriate (serial) bus for controller?

In the context of a robotic project where different 'payloads' and/or robotics arms (end-deflector) should be mated mechanically with power, data and control connections support, I would like to ...
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2answers
167 views

RS485 line protection diodes

Can anyone confirm the correctness of D27, D28 diode polarities or should they be in opposite direction? Please suggest an which diode is suitable for this purpose OR is it better to use a zener diode ...
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1answer
391 views

Does a MAX485 need decoupling capacitors?

I am designing a small device with two MAX485 chips. Do they need the decoupling capacitors on the 5V power?
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135 views

RS-485 Stub Connection Best Practices

I have a system with an RS-485 bus master and up to 12 slaves. The master and slaves are located in different assemblies and are connected with an RS-485 bus that is inside a cable harness. The cable ...
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1answer
62 views

Is it acceptable to have A & B wire at same voltage in RS485

I'm trying to implement DMX with a Raspberry Pi after reading this page: https://www.element14.com/community/groups/open-source-hardware/blog/2017/08/24/dmx-explained-dmx512-and-rs-485-protocol-detail-...
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60 views

DMX protection circuit (diode clipper)

TL;DR I’m building a board that bridges the common types of DMX connector (various forms of XLR, RJ45, tails and product-specific terminals). There is a possibility that someone could accidentally ...
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1answer
66 views

To Fail-Safe or not Fail-Safe on RS485/422 Transceiver

I'm stuck on a PCB design issue. I'm designing a new PCB (Daughter board) that will plug (via DB15-F to DB15-M) onto another PCB (existing Mother board) and the design intent is to take (from the ...
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1answer
78 views

Wireless or wired solution for perimeter fence security?

We are currently working on a project where we would like to place around 350 vibration sensors on our university's perimeter fence for security. The field layout is almost 1km to 1km (square - 1km^2 -...
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1answer
146 views

Rs-485 isolation

Hi, I have RS485 communication circuit as shown in figure. But it has no isolation, only SM712 is used for ESD protection. Now, i think it will be better to isolate the it.So, how can i isolate it? ...
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123 views

Why is there no reponse from ModbusRTU slave using converter?

There are two devices: Eaton EM20/M (~like Northern Design Cube 400) Volison ADM-5850G Connected them like: Trying to get data from EM20/M which supports ...
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2answers
84 views

RS485 termination

What is the recommended way for termination RS485? I read about couple of options to do this. If I don't want to do dissipate extra power, can I just put 120 Ohm resistor? I saw the follow ...
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0answers
73 views

RS485 registers for calculating total power consumption (kwh)

I have an energy meter (OHIO A2000) which has been now discontinued by the manufacturer. Anyway, I'm following the manual for extracting energy parameters through Modbus RS485 communication. I'm ...
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5answers
129 views

RS485 IC Termination Resistor Configuration

I've made a mistake on a design, that went into production... It was built like the drawing on the left, with R702 to 5V and R703 to GND, it should have been backwards... like the drawing on the ...
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1answer
50 views

Low current rs485 and wake up

I have the following question: I have to do a network of devices based on MCU. This network in a RS485 and the device is battery powered. For save the battery I put in sleep mode the MCU and I ...
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2answers
105 views

LIN to RS485 and back to LIN

I am currently communicating between two microcontrollers using a single pin and the LIN protocol over a short distance of 0.2m. Now I would like to extend the distance up to 5m by differentially ...
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3answers
359 views

ground connection for isolated rs485 [closed]

Is it necessary to connect isolated grounds for 2 different isolated RS485 nodes? For instance the following isolated RS485 breakout board doesn't have any GND connection in the board. https://www....