Design suggestion for a bus

Hi Michael!

definitely the solution should be based on a RS485 bus to simplify wiring

The customer just requires that, in case the board does not power on due to -typically- board's power supply failure, the communication continue to work.There is no safety-critical concerns there. I don't have an idea of the price he expects, but the production volume is about 20k pieces/year

Cheers

Ambrogio

Comment to myself

The dual ring unfortunately does not cover the "more-than-one-board-broken" condition!

Yes, was thinking the same. But that (allone) would not faciliate the failover capability. (unless I missed something)

It's not too difficult to protect the bus, use a fault tolerant drive such as LT1791.

If you need to detect which board is faulty, you can provide an ACK feedback bus.

This would fail if a single board fails and the ring is re-initialized

you say each board has an actuator of some kind attached and I assume each one is for a specefic purpose, so if one fails and re-initialization occures then assignements are now changed, unless all valves serve the same purpose, you must know the address of each valve in order to correctly control it

I2C only supports 127 Devices on a single bus, without I2C switches etc, you will not be able to change this, also it would be quite complex to make this fault tollerant . Also I2C devices have factory assigned addresses within a range, some can be changed enough to provide say 16 devices of the same make and brand on a bus but not much more. I2C probably is not your answer if you need 80++ boards stacked, all uniquely controllable and fault tollerant.

RS485 as mentioned earlier would be better, it is cheap, can easily cover the distance and number of devices and can be made into a ring, dual rings etc with little cost.

None of this though willl address how each board will self configure and allow the control master know who is who for specefic control purpose

Does each one need to be uniquely identified and controlled ?, can you say the purpose of the solution with a little more detail ?

I2C adressability is an issue. E. g. a suitable device could be TPS22993 Quad Channel Load Switch with GPIO and I2C Control but it features only 3 adress pins for a max of 8 devices. But each can operate 4 on / off valves. This would meet the stated requirements.

Then by that measure, using a device like a 23017  http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf  would give 16 valves on a board and reduce the count of boards considerably and only needs a couple of OCTAL Driver chips to interface to relays / Solenoids

I suspect this is compacting the control too much though but this is not known as your description does not provide too much of the operational details and is quite vague

If you can provide more details of how this will be configured and what it is controling we can advise better

Hi Peter

I will try to explain the problem

I have pneumatic valves that can be placed side-by-side as shown in this picture. You can (currently) have up to 38 valves

I need a board that controls these valves using a serial bus. There are two requirements:

1. If (let's say) the central board does not switch on, all the remaining valves must continue to work normally

2. The board must be "plug-and-play": when a board breaks down, the maintenance person take a spare part from the box, replace it and that's all

The obvious way to do this is to use Devicenet

https://www.google.co.uk/search?q=device+net+idc&ie=utf-8&oe=utf-8&gws_rd=cr&ei=8mO0VvPDI4fEOvCvgsAO

If actual Devicenet is too expensive you could trawl the extensive literature for ideas.

MK

Hi Michael

The obvious way to do this is to use Devicenet

Not sure why this is the obvious choice, since the devices will require a commissioning phase before installation and there are tens of industrial buses out there that are more widely used than DeviceNet

If actual Devicenet is too expensive you could trawl the extensive literature for ideas.

Yes, of course there is Google out there that can provide all the answers, but may be this community could provide suggestions based on hands-on experiences