Hello there,
For a project, 200 different controllers need to read a data that I produce in the center via wired communication. I am having a problem in choosing the communication protocol that I need to use for this. In this project, I need someone who has an idea about the communication protocol selection and how to use that protocol, or who can suggest a resource.

 

What data rate do you need and how far does the data have to go?

 

Some of the low power RS485 transceivers are specified at an eigth of a standard load, meaning that you can connect 256 of them to the bus instead of the usual 32.
https://www.ti.com/lit/an/slla166/s...15665&ref_url=https%3A%2F%2Fwww.google.com%2F

 

IP/TCP will do the job, and there are heaps of IoT examples out there.

 

Ethernet and TCP/IP or UDP, depending on the nature of the communication would be the naively specified best bet. But more information is definitely required to actually help.

 

IP/TCP will do the job, and there are heaps of IoT examples out there.

Thank you for your answer.
The communication I need to do will be wired, embedded systems will communicate. In fact, the dimensions of the communication units on the embedded system should be small. This solution seems like a good solution for wireless communication. However, I did not have an idea on how to do this in wired communication.

 

What data rate do you need and how far does the data have to go?

Thank you for your answer.
It will carry 128 kbytes of data. 400kHz speed will solve my problem. About 15 all receiving devices will be within a 15-metre radius.

 

Some of the low power RS485 transceivers are specified at an eigth of a standard load, meaning that you can connect 256 of them to the bus instead of the usual 32.
https://www.ti.com/lit/an/slla166/slla166.pdf?ts=1634721215665&ref_url=https%3A%2F%2Fwww.google.com%2F

Thank you for your answer.
I understand that you recommend CAN communication, right?

 

Thank you for your answer.
I understand that you recommend CAN communication, right?

No. i’m recommending RS485 with low power transceivers. CAN could achieve the data rate, but I don’t know of any low-power CAN transceivers that would allow 256 on the bus. Normally the limit is 32. I’m assuming you have a single sender and all the others are receivers. That would be easy in RS485 as you don’t have to deal with half-duplex and possible data collisions.
It sounds like DMX.

 

IP/TCP will do the job, and there are heaps of IoT examples out there.

Wouldn‘t it need rather a lot of hubs or data switches?

 

My choice would be RS-485.

 

With things like ESP32 as cheap as they are, I would go with WIFI and UDP multicast.

I am doing a project that way with one master, 8 slaves, and an http interface. I am using a Microchip board (pic-iot) for personal preference of the host processor (pic24.)

Edit: think of the savings on wiring!

Bob

 

Is this truly a case where all you need to do is "read a data that I produce in the center via wired communication"? If the communication has to be 2-way, then it gets considerably more difficult. That's because with a shared data link, you have to decide which of the nodes can transmit at any time. If they're all listening only, then they can do it without interfering with each other.

 

Is this truly a case where all you need to do is "read a data that I produce in the center via wired communication"? If the communication has to be 2-way, then it gets considerably more difficult. That's because with a shared data link, you have to decide which of the nodes can transmit at any time. If they're all listening only, then they can do it without interfering with each other.

They're all listening only

 

No. i’m recommending RS485 with low power transceivers. CAN could achieve the data rate, but I don’t know of any low-power CAN transceivers that would allow 256 on the bus. Normally the limit is 32. I’m assuming you have a single sender and all the others are receivers. That would be easy in RS485 as you don’t have to deal with half-duplex and possible data collisions.
It sounds like DMX.

Thank you very much
I will try this

 

A way to do this with RS485 could be to split the bus into multiple smaller buses, maybe 8 of them, each driving 25 receivers. You'd simply duplicate the transmitters as many times as you need to, and put one of them on each small bus; the components wouldn't cost much. Then drive all the transmitters in parallel.

 

A way to do this with RS485 could be to split the bus into multiple smaller buses, maybe 8 of them, each driving 25 receivers. You'd simply duplicate the transmitters as many times as you need to, and put one of them on each small bus; the components wouldn't cost much. Then drive all the transmitters in parallel.

Yes, that's probably what I'll do, thank you.

 

A way to do this with RS485 could be to split the bus into multiple smaller buses, maybe 8 of them, each driving 25 receivers. You'd simply duplicate the transmitters as many times as you need to, and put one of them on each small bus; the components wouldn't cost much. Then drive all the transmitters in parallel.

That would save money too, as they charge a premium for the low power versions.
Do bear in mind how much power is required. The cheaper devices are some version of old-fashioned TTL, and not a low power version! A 75176 needs 50mA. And you have to drive the 120Ω line termination resistors. It might be advisable to switch off the transmitter between messages to reduce the power needed for line termination.
There are qaud drivers (75174) which would reduce the component count.
I've also driven RS485 lines with a TC4428.

 

The MAX485 draws way less current than a 75176. There's also a MAX487, which they say can be on a bus with 128 receivers, but I don't know the relative cost.

There also needs to be a plan for how to power the 200 receiving units. Even if each one uses a small amount of power, it's going to add up.

Incidentally, the MAX485 is an expensive item if you buy from a US dealer--over $2.00 each, even in 100 quantity. But if you get them from China via eBay, and buy 50 or 100 at a time, they're less than a dime.

 

I have used LTC1487 ultra-low power RS485 in a battery powered remote data acquisition system.