Advice on making a quad-directional power/data connector

Question

I have an interesting problem that I'd like some input on. It's a bit complex, so I'll do my best to explain it clearly.

I have a connector with 4 pins arranged in a square pattern. The pins are designated as +, -, D1, and D2 (where D1/D2 is I2C). The challenge is that the solution must work regardless of the connector's orientation when it is plugged in (i.e., it must be position-agnostic).

I know this is a easy fix by just using a correct plug, but this is not what I'm asking. Question isn't really about the plug, but how to solve the problem for the plug I'm describing below.

Layout of pins can be changed to whatever could best solve the problem.

Here is a visualisation of the connection I have so far:

I have to make it so that no matter what way I attach a plug it will work. I can use a microcontroller and anything else I wan't.

I came up with a solution, but would like to see if I can get some better ideas or improvements.

If I add a bridge in this configuration I will get power no matter what direction the plug has connected:

Next I would cut the signal for A or B lines using P-MOSFET and note in my microcontroller memory what line I am cutting:

If my microcontroller is still working after a few milliseconds, it means it has correctly identified the power and data pairs. It then triggers switches to route the data lines appropriately. If it guessed wrong and cuts off the power pair, the system will reset, turning off the microcontroller and MOSFETs. On reset, the microcontroller will try again with the opposite pair, remembering the last state it tried.

Here is a quick sketch of the configuration I imagine:

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On a side note here is my first iteration I came up with that had 4 pins in a line. Left side is signal source and right side is slave device:

While this works it has some issues, and is not ideal because of some other constraints that I don't wan't to go into. Ideally I wan't to solve this for the 4 corner configuration.

Another thought was adding clock and data to the power rail with some opamp magic and then decoding it on the other side. But it probably is a lot more complicated than I imagine, considering noise, power draw etc.

Answer 1

I think this works, but I haven't simulated or tested it.

Here's what's going on: The mating connector must have power in the two corner pins, and I2C in the other two corner pins.

There are two bridges (with their outputs coupled together) to provide power to the MCU, and all four pins have pull up resistors connected to the bridge output positive. The MCU needs to have two I2C ports. You might need to add a voltage regulator to the power lines before the MCU.

Let's look at an example of it in use:

Here we've connected +ve power to the top right (red) and ground to the bottom left (black). I2C are the green pins.

The active I2C lines in this case are the orange ones.

If you were to use a PSoC microcontroller from Infineon to implement the I2C swapping, you'd need to implement a circuit inside it to perform the swap at run time (it's not a function already provided by the I2C component). This design uses two pairs of external pins, which would need to be connected together on the PCB (blue dashed lines). There's also a way to do it by reprogramming the configuration registers, but that would need some digging into the technical reference manual.

They're pretty low cost devices, but may not be cheap enough for your application.

Answer 2

Instead of four discrete pins, use a 4-circuit circularly-symmetrical connector.

These connectors may be plugged-in in any orientation. Regardless of orientation, each contact is connected to the corresponding contact in the mate. There is no need to detect the orientation and reroute the signals.

• In-line:
• • Helicopter headphone (top left)
• • 3.5 mm TRRS phone (middle left)
• Coplanar:
• • Concentric coplanar cylindrical (top right)
• • Flush concentric (bottom right)

{Sources: Digikey, Digikey, LEMO, Fischer}

Answer 3

You can also consider moving almost all inteligence into master - put current-limited H-bridge + i2c on each leg. On slave, put protection diodes on scl and sda (against + and - leg) and antiparallel diode between + and -. Master can probe (single) combination that is shorted by diode, then reverse polarity and communicate normally.

Answer 4

Is it a strict requirement that your I2C and power are run on separate sets of pins? If not, you can add a chip like the MAX20340 that will let you send and receive data over your DC power line, which makes your connector orientation issue significantly easier to solve (your original bridge circuit might be sufficient).

Answer 5

The correct answer is to use a stout plug that has survived for decades of use and costs a few cents.

Designing your own connector is expensive and error prone. However as an exercise, avoid a circuit-based solution and use geometry?

This assumes you have some lee-way to move the pins a little. If they're fixed in a square, this solution won't work.

One side : viewed from above. Each pin can land in any of 4 positions, which are simply pads on the same track and are joined together.

+-------------+
| - D2   D1 - |
|D1 +     + D2|
|             |
|             |
|D2 +     + D1|
| - D1   D2 - |
+-------------+

Other side: (for simplicity, this is viewed from above also, so mirrored or "through")

+-------------+
| . .     . . |
| . +     . D2|
|             |
|             |
| . .     . . |
| . D1    . - |
+-------------+