Best way to bus many cirucuit boards?

[eromlignod]

Hi:

I have an application where I have many (50+) individual, very small circuit boards, each with its own independent microcontroller. Each circuit takes more power than would be practical for batteries, so I have to run a power bus to all of them (+24, +5 and ground). I also have synchronous serial communications with all of them with TX/RX and clock lines (poor man's Ethernet) that eventually runs to a master circuit board.

Is there a neat/cheap way to bus lines to all these boards? I have tried header ribbon jumpers between each board, but it looks like hell and the short cables are stiff and hard to work with. The boards are very close together, but don't consistently align with each other, depending on the application, so permanent header plugs or edge connectors between boards won't work. Is there something clever or new (or old) that I'm unaware of? Thanks for replies.

Don

 

[VEBill]

Ethernet cable of the later Cat 5/6 types have 8 conductors (arranged in four twisted pairs). If you could find a flexible enough version of that, then perhaps it would be more convenient than stiff ribbon cables. Beware how the power and return and signals and returns are assigned to the twisted pairs.

Also, beware of running 5Vdc logic power supply over long distances. Induced noise might be an issue. If you're immediately regulating it down to +3.3Vdc, then you'd probably be okay. If you're using the 5Vdc directly, then be very careful and double check the stability of the supply.

 

[cranky108]

In some Remote Terminal Units they use a 400 Hz(could be higher) AC power supply to each board, mostly chained connections, And on each board there is the second half of the DC to DC converter to convert the high frequency power to something usable by the chips (I don't know the board internal power supplies). This also works with the twisted pair communications to each board, also chained connections, so the total number of connections for internal connections are two pair for each I/O board. Naturally the CPU and Power supply boards may have several pairs of connections, depending on the number of chains.

This arrangment makes additions easer, and also makes the I/O boards distributable throughout the substation (although the old guys never did that).

So the answer is to reduce the number of connections by using UARTS and power conditioning chips on each board.

 

[itsmoked]

From the little that's clear in your question I would heartily recommend the AMP brand MTA series of rectangular connectors.

They come in two sizes MTA-100 (0.100" spacing) and MTA-156 (0.156" spacing).
They consist of male pin headers of three types: Open Keyed, Open Keyed Locking, Closed Locking.

The females are all color coded to the wire size they accept. Since they are an insulation displacement connector the wire size needs to match the spades that it is staked into.

The female connectors come in two varieties: Closed and Feed thru. Wires end at closed headers but pass thru the open ones for daisy chaining.

You would want to buy the tools that you drop the females into to stake the wires into the connector's spades (I think there are two dies - one for feedthru and one for non-feedthru. The tool is very slick in that you poke the wire in, squeeze the handle staking the wire into the connector, then when you release the handle the connector is indexed ready for the next wire. Makes cable building very fast.

The connectors come in various offerings from 2 to about 10 positions. There are NO connectors as versatile or inexpensive as this series. For a pittance you can create a kit that will do almost any task you need.

Of course they come in gold or tin versions and straight or 90 degrees. Beware there are two species of 90 degrees, (normal and reverse).

Also beware that the distributors pricing depends on the quantities that are sold. You will find some oddities in that, say, an 8pin version may cost 1/2 what a seven pin version costs because vastly more 8pin versions are sold. So check around whatever size you need to see if adding a pin changes the price.

Example females:

http://www.digikey.com/product-sear...ectors-free-hanging-panel-mount/1442549?k=mta

Example males:

http://www.digikey.com/product-sear...ar-connectors-headers-male-pins/1442547?k=mta

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MikeHalloran]

I've always liked iso-async mode, uart divisor=1, tx,rx,clk distributed.

The first thing that came to mind was Zebra strips sandwiched between the boards.
I would worry about high currents and shared impedances, though.

Also, be aware that there are standards, and I think a trade association, for distributing power over Ethernet. I stumbled over it just the other day; search on POE or something similar.



Mike Halloran
Pembroke Pines, FL, USA

 

[LiteYear]

Neat solution we've used recently is a bus integrated into a DIN rail. Eg:

http://www.phoenixcontact.com.au/news/248_16059.htm

Not sure if you can mod your boards to suit, but if so, something to consider.