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As a follow-up for my previous question, can anyone please recommend for my application (communication between two floors of a building) as whether to use RS-485 or any wireless technique (I am thinking of using cheap 433 MHz based ASK transmitter or please suggest if there is any other low-cost wireless solution for my need).

The typical datarate for communication will be around 115200 bps. I have also heard of ZigBee OR XBee but I want to go for a cheaper option (but reliable too in terms of data integrity, as the application involves sending 2-3 types of sensor data which play an important role in my feedback system).

Any suggestion is appreciated.

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  • \$\begingroup\$ It all depends on what you mean by "reliable". \$\endgroup\$
    – Andy aka
    Commented Sep 29, 2020 at 17:09
  • \$\begingroup\$ Wireless is never completely reliable. But it's much easier. You decide. \$\endgroup\$ Commented Sep 29, 2020 at 17:21
  • \$\begingroup\$ @user253751 Thanks for the point you just mentioned, being specific about my problem, I wanted to ask if there is any low-cost better alternative than 433MHz ASK modules. \$\endgroup\$ Commented Sep 29, 2020 at 17:23
  • \$\begingroup\$ If you've never used an RF module before, be aware, the details can become very complex. \$\endgroup\$
    – rdtsc
    Commented Sep 29, 2020 at 18:06
  • \$\begingroup\$ I am a fan of hard wires, so go for RS485. I was never impressed by WiFi modules, but this is just my opinion. \$\endgroup\$ Commented Sep 29, 2020 at 21:19

2 Answers 2

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Your previous question implied you were going to run wires for power anyway, at which point there's little reason not to use wired communication. There are also plenty of schemes for modulating data onto power wires; those work especially well if you use a higher supply voltage and regulate at the receiving end.

Adding an actual radio brings many new challenges - interference, range, obstructions which shield, susceptibility to power supply noise, regulatory...

Those regenerative 433 MHz ASK systems are truly horrible and would not support your desired data rate to begin with. Better 433 MHz FSK data radios which interface via SPI are available, but cost more.

Typically the cheapest radio solution is 2.4 GHz nRF24L01+ clones, typically a dollar per end, reasonable range, reasonable rejection of AM type noise sources, lots of hopping channels for deconfliction and a digital packet scheme to which checksums and even encryption is easily added. You'll also find lots of example code support for common platforms like Arduino, MBED, raspberry pi, etc.

In theory the 433 MHz FSK systems would have better wall penetration, but at a higher cost of 2-3 dollars per end. Going further still, LoRa radios have a unique modulation which provides more probability of success in situations with a poor ratio of signal to noise in both intereference and marginal range cases. But that's more on the order of five to ten dollars per end.

Ideally use wires not radio. If you do choose to go the radio path, look at the "Radio Head" library and see if your chosen radio type is supported there; writing radio code from scratch with only the data sheet register description as a guide in a painful process, especially if tackled without previous experiencing changing the details of similar already working systems.

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Guess if you ask 10 people here you get 11 answers. so here is mine:

for wireless you normally need a protocol which can handle transmit errors... So I would prefer a cable solution if feasible to have a cable

115kbits/s with max 10m? why not Rs232? to be honest almost anything will be possible with this data-rate and distance. Guess even USB 1.0

PS: long distance communication is not 10m... its maybe 50m or 100m and more.

I would guess 10(0)Mbit/s Ethernet might be a good choice also, plus it has as standard for power over Ethernet (as you seem to want to transmit power too).

RS485 definitely can do the job, but you need a protocol which can detect transmission errors also (with Ethernet you get all that of the shelf).

another good choice would be CAN, here the Hardware also provides a lot of things you need to cover by SW in case of RS485

  • From a complexity point, Ethernet is the worst, but almost anything you can buy as a of the shelf solution or get as OpenSource - plus its easy to debug with an PC and wirehark.
  • My next best choice would be CAN - µC are a bit more expensive, but the rest of the Hardware is easy and also SW for basic communication is trivial.
  • My least favourite solution would be RS485...
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