We ran an article this week about RS-485, a noise resistant differential serial multidrop bus architecture. (Tell me where else you’re going to read articles like that!) I’ve had my fun with RS-485 in the past, and reading this piece reminded me of those days.
You see, RS-485 lets you connect a whole slew of devices up to a single bundle of Cat5 cable, and if you combine it with the Modbus protocol, you can have them work together in a network. Dedicate a couple of those Cat5 lines to power, and it’s the perfect recipe for a home, or hackerspace, small-device network — the kind of things that you, and I, would do with WiFi and an ESP8266 today.
Wired is more reliable, has fewer moving parts, and can solve the “how do I get power to these things” problem. It’s intrinsically simpler: no radios, just serial data running as voltage over wires. But nobody likes running cable, and there’s just so much more demo code out there for an ESP solution. There’s an undeniable ease of development and cross-device compatibility with WiFi. Your devices can speak directly to a computer, or to the whole Internet. And that’s been the death of wired.
Still, some part of me admires the purpose-built simplicity and the bombproof nature of the wired bus. It feels somehow retro, but maybe I’ll break out some old Cat5 and run it around the office just for old times’ sake.
47 thoughts on “The Virtue Of Wires In The Age Of Wireless”
Living in a 400 year old house, wireless has an incredibly limited and patchy coverage – that includes network, bluetooth and mobile telephony – which makes most of the commercial products such as wireless weather stations a non-starter.
For me, the solution has to be wired. A network to serial interface allows me to talk with my remote projects without needing more costly microcontrollers to handle newtork protocols and RS-485 to deal with the instrument cluster. Since I’m going to be running wires anyway, it is no effort to provide power to my projects at the same time.
Oh, and I tend to stream data using an NMEA 0183 style sentence format, which effectively pre-parses messages as data, status, priority and error codes as well as telling me where the data is being streamed from.
No, in my own opinion, it will be a long time before single-ended and differential serial signalling goes the way of the dodo.
At no point in your rambling, incoherent response to wireless were you even close to anything that could be considered a rational thought. Everyone in this room is now dumber for having listened to it. I award you no points, and may God have mercy on your soul.
He did mention power transfer for one thing … maybe you need to read it again.
Man, that movie did NOT age well..
Just finishing up a major remodel of my new house. Ran about 6,200 feet of CAT-6. multiple pulls to every room (except the bathrooms :-)). PoE rocks.
You’ll live to regret that. No thematic PoE powered RGB lighting in the bath or nightlight for the midnight pee? No soundtrack in the bath… (Alexa PoE?) No humidity or motion detection for smart, ahem, extraction? No eco-friendly towel rail heating… The bathroom has rich pickings for automation, more so than any other room in the house I’d wager, apart from possibly the ‘cinema’.
This is a huge thing that I will be doing in my future home… It just makes so much sense!
Ethernet cabling to each room for devices, and I want to have divided boxes so that I can have a high/low voltage mixed in the boxes with the lightswitches for some nice IOT panels.
Gonna be a heck of an MDF in the utility room though. ;)
don’t forget one cable to the top of each window for status information (closed/open1/2), burglar alarm (glass-breakage sensor) and maybe control of the motorized roller shutter.
And maybe pass it along near the ceiling lights (smoke detector).
And while we’re passing along hints. Allow plenty of slack and a service loop at both ends. I built a house decades ago and wired it in the Summer (simple twisted pair from Radio Shack). Along came winter and a couple of my sensors stopped working. I easily ruled-out a sensor issue. When I finally managed to get back up into the attic, several of the wires had apparently contracted and snapped due to tension induced by the cold.
Taut wiring is a “closeline”. A short cut past corners. I fire anyone that tries to pass that off as professional grade. Anyone that installs wiring closelines is simply lazy, uninformed, can’t think ahead or simply doesn’t care. Sounds harsh? Yeah… depends on perspective and adherence to wiring as a practical art and serves a purpose and looks and performs great too.
Except for rare cases or a device that actually moves around regularly, give me wires every time.
RS485 and Modbus, let me go fire up the calculator and pen plotter so I can write some HP basic, ya know the world has moved on
What do you mean by that?
Pen plotters are mostly museum pieces and HP has degraded to shoving laptops and standard PC’s but modbus and RS485 is very much alive. Modbus is royalty free, easy to use and it is “good enough” for lots of automation jobs. Remote I/O modules for modbus are common. Lots of frequency inverters are compatible with modbus. I’m not sure about “more advanced” motor controllers. EtherCat is one of the options, but it’s also common for gadgets to support modbus RTU too for jobs where it is “good enough” and which do not need nor want the extra complexity.
If it’s not good enough for you, you’re free to use something else.
Most people don’t even know about a bus system that is open source and stomps ethercat and the like into the ground in many aspects. It’s from a plc manufacturer in Austria B&R. It’s called “openPowerlink” and after seeing the realtime applications done with it, I would go for it any day.
You can do EtherCAT on open source too. For controllers (master) you can use erherlab and SOEM, and just use ethernet RJ45. There is even linuxcnc integration if you need gcode interpreter or free soft PLC
If you need to build slave devices you can use EasyCAT board, and register for free in Ethercat organization and get their codegen tool. Or use free SOES library
The amateurs only want to use WiFi because it’s all they know. They burn through batteries so fast each fills their own landfill.
The pro kids like to jump straight to CAN bus solutions because they can’t bare to be seen using something old or slow.
The pro adults realize that all those high frequency impedance issues, expensive chips and proprietary protocols aren’t worth it when all you need to do is turn something on and off or maybe collect a little telemetry so ModBus is still going strong.
With RS485 you can get higher throughput and lower latency than with CAN (at least legacy CAN not sure about CAN FD)
You might have to dump Modbus for some application specific protocol, but HW would stay the same.
Try build motion control system doing something useful on wireless network, and let us know how it went, bucko.
While I am yet to spend anytime on it and don’t work within motion control anymore, I did read that 5G supports determinism. I agree to a (currently) unknown extent.
It needs to be resistant to strong nosie inducted by AC motors or płaska cutters too. No way for RF thing to be as good as differential pair in shielded cable
Is motion control the topic here?
What makes things like ESPs appeal to me over something like RS-485 is the use of the TCP/IP stack. I can make projects that easily communicate with a countless number of devices either sitting right next to me or across the world. It’s perhaps not the best solution for everything, but it does well for the jack of all trades.
With enough effort, Tcp/ip will run over just about any medium including carrier pigeons.
When you get tcp/ip up and running on smoke signals, be sure to give us a write up.
Dude! We’ve been signalling you for *hours*! Look out the window occasionally!
Now go find some dry leaves and send us an ACK packet.
TCP/IP stacks are so heavy!
If I have a bunch of embedded controllers all in the same building and they are controlling moving things where timing matters I’d rather a local Modbus network with a single Modbus to MQTT gateway somewhere.
If they don’t need real-time synchronization then maybe an NRF network with an MQTT gateway. But then again, I do hate batteries so at least power wires need to be ran anyway. Depending on where that power is coming from maybe it should just be RS485.
Our sales guys would always come by to try and talk me into a wireless version of our product. One that we installed into a purpose built room at the client site. Wireless just sounded cool. I use it occasionally but relish the convenience of sending both power and comm to a device with just a simple cable.
Power is always the problem it seems. I’d like to put a device here and there and everywhere and use wireless to access… sounds easy…. but then you realize you always have to run power to all those devices (or a bunch of batteries which isn’t practical). So why not just run data and power with same cable to the device. More secure (not blasting wifi out), reliable and you certainly don’t need high speed comm to tell you door open, door closed, temperature, etc. :) . Of course the other option is just run wires from sensor all the way back to a central termination box. That is how I think I am going to approach the problem as it will keep the power management … manageable. Only a few devices then needed, but a lot of long cable runs.
There is one potential gain to wireless – it transmits even if the signal line is down, so with battery or alternative power it should ‘always’ work.
That said PoE really is better 99.999% of the time, its just so simple and you can even get outdoor rated PoE capable network gear and cables great for things like security cameras, which are the obvious case in point of it being by far the best way to do it – who wants to broadcast what their security cameras are seeing in an way so trivial to pick up?
Most of our house has been wired with Cat5 for many years, though we also have WiFi. Wired is more reliable, so we have USB docking stations in strategic locations for our laptops. Also, I still use a wired mouse because it’s easier to retrieve when it falls (and limits how far the cats can knock it when they play field hockey with it).
I’ll just leave this here:
Wired headphones/earbuds are making a comeback. No more fiddling with earphone batteries, no more loosing them.
exactly. and you can get wired earbuds with smaller footprint so they dont hurt your ears while takin a nap with em in. also, MUCH cheaper. and the jack will never truly disappear. i refuse to have a music device without a jack. with one exception, i have some 30 dollar jbl bluetooth over the ears i use so i can work and listen in loud environments or otherwise work hands free when im away from my hand built ghetto blaster or other devices.
Novel concept … plug it in and it works! Better yet, unplug it and it stops working instantly! Imagine that!
SPE and PoDL
One of the decision-driving aspects of the home we bought in Colorado last year (built in 2005) was the existing Cat-5 cabling with anywhere from 1 – 3 drops per room. That, coupled with the city’s providing symmetric 1Gb fiber as a utility at the flat rate of $70.00/mo made the choice pretty hard to pass-up. Love the home, the access and fast uploads! Totally spoiled!
Wireless solutions are great for old cars. You can put the sensor in the engine bay and the display inside and not have to drills more holes in the firewall.
But a good old wired solution is nice too. I let “power distro” determine what I do. If there’s already power everywhere, wireless is the way to go.
I love wires and I’m really mad all the modern dimmable, coloured light bulbs can only be used over wifi, and often with proprietary protocols (Tuya-Convert is dead, and only Athom sells preflashed Tasmota bulbs).
RS-485 and Modbus has one huge problem: the end devices can’t initiate communication. This is a deal breaker for light, curtain or doorbell buttons and switches. Wifi deals with this easily, while Modbus needs to query all devices independently which causes delays and unnecessary bus load, where all devices need to wake up and listen to what the master is saying (and frankly, I’ve never seen any Modbus switches).
KNX solves this and is in my opinion a much superior protocol. It’s even an open standard, yet it’s still incredibly expensive. A Gira 6-way pusbbutton with LEDs costs around $200 in retail, which is pure crazy.
One other great feature of KNX is that it can power devices using the same twisted pair that transmits data.
I really would love to see KNX get more adoption.
I could be mistaken, but for the manufacturer the KNX licensing fees are not cheap… and I think one is forced to use KNX specific tools. Bacnet is much nicer and license free. The actual Bacnet spec does cost $, but is not overly expensive and is a one time cost. Bacnet supports IP and MS/TP which uses RS485. Bacnet is a Standard and is used throughout North America and so there are lots of gear that support it.
You can always just go with PoDL for your RS-485. Just takes a few inductors, capacitors and a common mode choke. Used all over the place in industrial encoders. Just look at Sick’s DSL or EnDat 3.0.
I am remined of the only person who could elegantly describe Modbus to me. He worked for Modicon and his quote to remember was, “Even cockroaches use Modbus”
My workplace produces a small embedded device that communicates with a 22dBm 2.4GHz 802.15.4 radio and samples data from a locally-connected Modbus energy meter and a pulse meter (for water or gas).
Muggins writes the firmware for it. It was originally designed for caravan parks and marinas, install these things in the pedestal where the boat/caravan connects up for power/water, and you can meter (and control) access to these utilities. While there’s (obviously) power going to these sites, there’s often not data communications because electrical regulations prohibit running copper data cabling in the same conduit as power, and fibre optic is expensive.
The latest use case though has been existing buildings that may have fire-rated floors though which they can’t drill holes to run new RS-485 or Ethernet runs. +22dBm at 2.4GHz can _just_ make it through 3 of these floors. I would argue that running an optic fibre through that floor would be more cost-effective, but I’m told wireless is “what they want”.
In Australia, we can run +22dBm without issue. In the USA, we’ll have to drop our transmit power by 2dB on channel 26. (Already written the firmware feature to do this), and hopefully that’ll still make it through at least two floors.
In the EU though, the limit is +12dBm… that’s not going to make it through rebar. Explaining this to non-radio people is the biggest challenge. (Ohh, can’t you just get a bigger antenna? No, because the limit is EIRP so the antenna is part of the equation!)
The other fun incidents related to this is when a colleague installs a 4G router in a basement and wonders why the performance is so poor. “Can we use a better antenna to fix this?” “No, because you put it in an imperfect Faraday cage, no antenna design will fix that”.
Wireless has its uses, but there are places where it is simply Not The Right Tool. On something that moves, yes, wireless is great. I for one like being able to maintain a discussion with work colleagues whilst I get up to go put the kettle on — a wired headset would have me chained to the desk via my head. If it doesn’t move, just run a cable to it. It’ll be less trouble overall.
Cellular communications on the go is great, but at home I use a fixed broadband link because 4G is prohibitively expensive. My portable laptop uses WiFi (but can use Ethernet when speed is important), but my desktop PCs all use Ethernet.
Only place I’ve heard of it being the other way round is in places like Norway where the ground is largely rock — it’s easier to spend big on one trench to a tower then go wireless for the “last mile” then it is to feed each and every house. I don’t have that problem here in Brisbane.
However, a wired link is usually much more reliable with fewer things to go wrong. I’ll take wired over wireless any day unless there’s a significant practicality reason to do otherwise.
Good info on Zigbee vs WiFi. Looked up the Channel 26 reference and found it is the last and highest channel at the band edge. Found this useful article on WiFi and Zigbee coexistence… While avoiding Channel 11 is possible for a home, that is not possible in any commercial venue: https://www.metageek.com/training/resources/zigbee-wifi-coexistence/
One of the best things about using a wired connection is it leaves spectrum open for other things. Less traffic also helps keep the noise floor low meaning fewer dropped packets.
I’m so glad we use good old fashioned wired EKG, blood oxygen meters etc in the operating room and hospital. I couldn’t imagine dealing with connectivity issues let alone data management and privacy protection concerns while a patient is tanking.
CAT is over kill, I simply run 4wired telephone cables, twisted pair is over rated in noise free environment.
12V, gnd, A,B
Is this a tech I can use to remotely control two 240v heaters? Can anyone point me to a guide, or resources? I have been having a hard time trying to track down options for this. I planned to use an arduino to run a web server to control two relays, but the amps for most of the relays around are too low. I realized recently I might be able to tap into the power switch which hopefully runs on fewer amps.
Any guidance/assistance appreciated.
Please be kind and respectful to help make the comments section excellent. (Comment Policy)