RS485 resistors

Started by Marco Trapanese in sci.electronics.design10 years ago 9 replies

Hello, I'm talking about the usual RS485 front-end: MAX485, series resistors (if any), pull-up/pull-down and termination resistor. The...

Hello, I'm talking about the usual RS485 front-end: MAX485, series resistors (if any), pull-up/pull-down and termination resistor. The system I'm working on has two RS485 transceiver at both ends of a twisted-pair cable. Its length is between 250 m and 500 m. I'm wondering how to dimension the resistors' values. With "standard" values (4k7 pull-up/down, 220 termination, 10 series)...


Powering isolated RS485 transceivers over cable

Started by markp in sci.electronics.design7 years ago 7 replies

Hi All, I have an application that requires about 12 sensor devices over a RS485 cable, evenly spaced over about 20m with a controoler at the...

Hi All, I have an application that requires about 12 sensor devices over a RS485 cable, evenly spaced over about 20m with a controoler at the end. I'd like to use galvanically isolated RS485 buffers such as IL3185 on each sensor, but would also like to not have to put isolated DC-DC converters to supply the power to the cable side of the buffers. So can I supply +5V up the cable to al...


RS485 grounding part 2

Started by mkr5000 in sci.electronics.design9 years ago 16 replies

I've read some material (a Jan Axelson article), that further confuses me on this matter of proper RS485 grounding for the shield that surrounds...

I've read some material (a Jan Axelson article), that further confuses me on this matter of proper RS485 grounding for the shield that surrounds our twisted pair of data. Like I say, I have always just grounded just one end to a good EARTH ground, either my transmitter or receiver, depending on the "best" ground available at either. The xmtr for example may be mounted closer to an electr...


Surge Pulse Clamping with Ceramic Capacitors

Started by Klaus Kragelund in sci.electronics.design4 years ago 40 replies

Hi For an application I need to protect the electronics of an RS485 interface from surges (8/20us 1kV pulse) The normal way be to use a...

Hi For an application I need to protect the electronics of an RS485 interface from surges (8/20us 1kV pulse) The normal way be to use a transzorb, in a SMA housing or even a SOT23 device. That is not possible since we have to be able to withstand up to 30V DC on the bus also (that is handled by a special RS485 IC) The problem is that the selected breakdown voltage of the transzorb ...


RS485: testing loopback

Started by Ajab in sci.electronics.design10 years ago 4 replies

I am using a rs232 to wire rs485 converter. I have shorted TX+ with RX + and TX- with RX- for 2-wire configuuration. A 120R termination resistor...

I am using a rs232 to wire rs485 converter. I have shorted TX+ with RX + and TX- with RX- for 2-wire configuuration. A 120R termination resistor is connected between TX+ and TX-. I am using it in half-duplex configuration. Is it possible to test loopback. Because in half-duplex either tx or rx will be enabled. I have not tried this. Just before trying want to check if this will work.


RS485 trouble

Started by ScadaEng in sci.electronics.design7 years ago 34 replies

I have worked allot with RS232, and other serial protocols, but this is my first RS485 project. It seemed straight forward to me, but now I have...

I have worked allot with RS232, and other serial protocols, but this is my first RS485 project. It seemed straight forward to me, but now I have a big problem. I am using the max490 chip. I'm doing full duplex, 4 wire. Each of my nodes have the max490 communicating with a 16F877A pic chip. The whole project will have 25 nodes. I just built two pcb's (nodes) and individually they work ...


rs485 bus on preamp not working

Started by bill13 in sci.electronics.design8 years ago 2 replies

i suspect it will take the audience about 5 secs to realize I am a novice but I have an interesting problem and would like to see if experts can...

i suspect it will take the audience about 5 secs to realize I am a novice but I have an interesting problem and would like to see if experts can make a novice into a functional apprentice via the web. In simple terms: I have a preamp that connects to keypad through a rs485 bus communiction port. My keypad's leds all are on red and the trouble shouting brochure states that this means that i ha...


Discrete custom design of RS485 driver

Started by Klaus Kragelund in sci.electronics.design4 years ago 111 replies

Hi The standard RS485 drivers available has a minimum voltage of 3V and a rarther large drop voltage when loaded with the defined bus load for...

Hi The standard RS485 drivers available has a minimum voltage of 3V and a rarther large drop voltage when loaded with the defined bus load for Modbus of 54ohms, and this causes problems for our design since we have limited power available for driving the bus So, we are thinking about designing our own driver in discrete components, so we can reduce the supply down to 2V and still comply with...


rs485 and RTN

Started by ice in sci.electronics.design6 years ago 21 replies

hi all system: 9600bps rs485 half-duplex with single master and multiple slaves; both master and slave connector have 3 pins (A,B,RTN) cable:...

hi all system: 9600bps rs485 half-duplex with single master and multiple slaves; both master and slave connector have 3 pins (A,B,RTN) cable: about 500mt shielded cable with 2 twisted pairs inside, one pair used for A/B signals other pair used for RTN the system works well questions: 1. the shield of the cable is connected to earth ground (yellow-green wire) at master side only: is t...


Lighning protection

Started by Phil Hobbs in sci.electronics.design2 years ago 35 replies

So I'm looking at lightning protection for the mezzanine units of the cotton spark detection system. I have a copy of Standtler's book,...

So I'm looking at lightning protection for the mezzanine units of the cotton spark detection system. I have a copy of Standtler's book, "Protection of electronic circuits from overvoltage", which is useful but a bit out of date (1989). (He doesn't know about HV depletion MOSFETs or polyfuses, for instance.) It looks as though I can protect the isolated RS485 pair and the power/commo...


Alpha & Omega AOZ1282 buck regulator--experiences?

Started by Phil Hobbs in sci.electronics.design2 years ago 10 replies

Hi, all, I'm doing the back end for that cotton spark detector system. Each integrator box (Pi Zero based) digitizes the output of up to 8...

Hi, all, I'm doing the back end for that cotton spark detector system. Each integrator box (Pi Zero based) digitizes the output of up to 8 sensors and talks via multimaster RS485 or maybe industrial CANbus to a control panel, which sends data to the outside world. (Getting the SCADA security right is the client's job--I bowed out of that bit because I'm not a crypto guy.) I need a 24V...


OPC driver/Software question

Started by Maynard A. Philbrook Jr. in sci.electronics.design3 years ago

I have a device that I made and it has RS485 on it, I put a compatible Modbus firmware in it and wrote a DDE server for the windows HMI...

I have a device that I made and it has RS485 on it, I put a compatible Modbus firmware in it and wrote a DDE server for the windows HMI front end, which seems to work with the custom HMI I wrote and others that are on the market.. There has been chatter that NetDDE is not supported any more and maybe DDE could be short lived, so I was looking into using the OPC as an option which...


replacing a rs485 transceiver chip

Started by bill13 in sci.electronics.design8 years ago 2 replies

I am going to replace a transceiver chip on my preamp so it talks to my keypad which by the way has the same transceiver in it (max1843)....

I am going to replace a transceiver chip on my preamp so it talks to my keypad which by the way has the same transceiver in it (max1843). Typically I have no trouble soldering but I am new at surface mount. I am willing to take shot at it. Whats best heat gun and solder paste or solder gun and solder? --------------------------------------- Posted through http://www.Electronics-R...


SPDIF to AES/EBU

Started by Dirk Bruere at NeoPax in sci.electronics.design8 years ago 5 replies

Looking for a reliable circuit for the level conversion from SPDIF to TTL. I then intend to feed it to an RS485 driver and into a transformer...

Looking for a reliable circuit for the level conversion from SPDIF to TTL. I then intend to feed it to an RS485 driver and into a transformer for transmission via CAT5e -- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.theconsensus.org/ - A UK political party http://www.blogtalkradio.com/onetribe - Occult Talk Show


Network of MCUs with centralized power supply

Started by pozz in sci.electronics.design2 years ago 18 replies

I'm going to develop a network of 10-30 electronic nodes based on MCU. The distance between them could 100m maximum. There is a single centrale...

I'm going to develop a network of 10-30 electronic nodes based on MCU. The distance between them could 100m maximum. There is a single centrale power supply unit (PSU) that gives power to nodes through a low-voltage 12-18Vdc plus/minus cables. I'm thinking about a two-wires half-duplex RS485. I'll have 4 cables (+/- for power and A/B for signals) and the advantage of differential signal...


Strange high frequency push pull transformer action

Started by mook johnson in sci.electronics.design5 years ago 100 replies

As mentioned before I'm working with a design that has a 10MHz push-pull transmitter to drive a 100 ohm cat6 cable. The cable is terminated...

As mentioned before I'm working with a design that has a 10MHz push-pull transmitter to drive a 100 ohm cat6 cable. The cable is terminated with 100 ohms on both ends and the length is ~200 ft. This is a multi-drop implementation much like RS485 but needed custom drivers due to the environment. The driver is configured as a push pull with 5V on the center tap. The 2n7000 transisto...