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Module layout proposal

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Paul KocylaPaul Kocyla 02/11/2016 at 14:366 Comments

Proposal for the module board:

Modules are arranged in a 2x2x5 matrix = 20 modules in a single PocketQub
Eight long pinheads go up through the five modules of each quadrant.
Here is a picture of the proposed pinheader,
Five pins are unique UARTs (halfduplex) for each of the five modules in one column, additionally a +3V3 and a GND pin.
I planned a unique power latching for each module, but this would require additional five pins. Instead, there might be a latching for each column, and to prevent other modules of this column to be shorted by another module, I´d suggest to use a polyfuse on each module mandatory.

Let me know if you got a better idea to arrange/connect the modules which saves more space.

NOTE: I don´t want a bus system, because I want to avoid unnessecery coordination between the modules´ owners and avoid a bus failure if one module shorts the bus.

Discussions

Frode Lillerud wrote 08/07/2016 at 09:22 point

What type of connector is this?

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Paul Kocyla wrote 08/07/2016 at 17:35 point

This is a connector from würth electronics with a through hole to pass the pinheaders through multiple boards. This was just a proposal. Maybe there are better connectors around which save space on the boards.
You are welcome to participate in this project - the design has not been defined by this time, so everything is open yet.
The idea is to find 20 participants who design one board each and make a complete system in the end.
The launch/test costs can be divided by the number of participants so we can afford a launch of an 1U pocketqub

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Frode Lillerud wrote 08/07/2016 at 19:42 point

I saw the slightly larger PQ60 form factor is using a 60-pin board-to-board connector from Hirose. Maybe something similar can be used for this smaller formfactor as well. I haven't used any of them, but there are quite a lot of "Stacking Board Connectors" on Farnell.

I was intrigued by the PQ60 form factor, and I'm going to make a couple of boards to test the connector they use. I know PQ60 is a lot bigger than this project requires, but maybe I'll pick up some good ideas along the way.

The PQ60 group should define a PQ30 form factor as well that is about 1" x 1", and with a smaller header. That would be what this project needs.

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Vivek Vaid wrote 06/08/2016 at 19:28 point

Hello, 

Sorry if the following suggestions or comments are too late and seem not relevant-

How about a CAN bus (common in automotive) as it is very highly reliable and differential, and many modules can be on same 2 wires. Coordination is automatically managed by CAN block withing MCU. You just need to assign different base address to each module in software and ask them to limit their CANid to a range

1.b if the host requirement is to have UART, maybe one node can be CAN to UART translator.

1.c To reduce shorting potential, mandate a common CAN transceiver IC from are reliable company like Infineon, Automotive grade (instead of commercial, iits just few cents more).

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Samuel A. Falvo II wrote 06/08/2016 at 20:40 point

1.c.  Even this isn't a hard requirement; use open-drain or open-collector logic.  That way, driving the signal consists either of pegging it to ground, or letting it float (a pull-up resistor is used to restore the 'high' voltage level).  On a MCU without built-in CAN-bus technology, you can bit-bang this by setting the output for an I/O to low, and just switch the I/O pin between input (float signal high) and output (drive low).  As a side benefit, when you float a signal high, you can also use the same I/O pin as a real input for true bidirectional behavior.  No need to use two I/O pins as you might find on some designs.

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Paul Kocyla wrote 06/08/2016 at 20:44 point

Yes, that seems to be the best way to do it. We already changed the development into this direction. There will be only four wires: +,GND and CAN

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