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1  Products / Arduino Due / Re: Solution for the 5V vs 3.3V problem on: December 17, 2012, 04:54:50 am
I can't see where the data sheet says this is possible, apart from two OE and two DIR pins there are no control signals.


Hey Rob,

Guess I had an optimistic read on that datasheet, you are right. Here is my solution.

With the setup, each pin can be selected as 3.3v or 5v through the MUX, then routed through the logic shifter if it is 5v. After that, the crosspoint handles the pin reassignment if needed. How about this? We getting close?

2  Products / Arduino Due / Re: Solution for the 5V vs 3.3V problem on: December 14, 2012, 04:31:21 am
Ok so here's the diagram of the circuit as I see it. Let me know what you guys think

Circuit for pins who's position might need to be changed

And here is for the other pins who's position is fixed

For both the CD22M3494 (crosspoint) and the SN74LVC16T245 (logic shifter) I think the buses can be 16 bit wide. As for going with the SN74LVC16T245 over the TXB0108, the advantage I see is that with the SN74LVC16T245, you can select each pin's output so some pins could interface with 5v logic, while others with devices at 3.3v. Might as well keep the shield dynamic as we can, especially if things really are moving towards 3.3v logic. Just my two cents, what's your guys reaction?

3  Products / Arduino Due / Re: Solution for the 5V vs 3.3V problem on: December 12, 2012, 05:26:15 pm
Hey Rob,

Here is what I'm thinking. This first drawing is a rough schematic for just the crosspoint section of pins. Other pins could be added to these and all the rest of the pins would need to be passed through 74LVC16245's as well.

Red trace is on bottom

Blue is on top

Black is on bottom (5v, 3.3v, gnd)

To answer you question about the pins, Mayhew Labs came up with a pretty nice solution.

As you can see, the headers don't go through the pcb, but are instead surface mounted. This way, we could have separate top and bottom circuits.

4  Products / Arduino Due / Re: Solution for the 5V vs 3.3V problem on: December 12, 2012, 03:37:51 am
Being able to select/designate individual pins as 5v or 3.3v logic
Needs a lot of hardware, in banks of 4, 6, or 8 not so bad.

A crosspoint switch would be one way to go, you'd need a lot for them and last I looked they were not cheap. Also I don't think they level shift but at least they should pass the analog.

As for the analog you can get programmable gain chips or just make your own with opamps.

Either way you need more IO to control this lot, so add 1 or 2 I2C IO expander chips with jumpers to set the address so they don't clash with any shields.

In general I like the basic concept but it could very quickly turn into a cluster f*ck with 30 chips that cost 2x the Due and the shield you want to use.

Crossroads (aka derekmjenkins!?), you've obviously made a start, any thoughts on doing something?

Are there many mega shields?
I don't think so, I'd drop the extra stuff and just go for a standard shield.

EDIT: I just looked at the price for that CD22M3494 crosspoint switch, it's not too bad but still too much for this I think.


Hey Rob, got a solution for ya.  (I think there is a 32 channel unit as well)

Use something like this after a crosspoint switch and before exiting the shield. That way, each pin's output voltage can be selected and each pin can by dynamically assigned. Also, why do you think this would be too expensive? Mouser has the level shifter I just mentioned at $2 and the crosspoint at $4 or 6. Plus other parts and custom fab, you could almost surely get away under $20.

EDIT: Just thinking, you would just need the crosspoint for the pins that need to be moved like SCL and SDA, then just use a couple more of the level shifters I mentioned for the rest of the I/O. That way, the pins that might need to be moved can be, while all the pins can still be selected to be either 5v or 3.3v.
5  Products / Arduino Due / Re: Solution for the 5V vs 3.3V problem on: December 11, 2012, 06:45:41 pm
Hey guys,

I've been looking into something like this for a while as well. One thing that caught my eye was this pin converter shield for the UNO/Leo to go between the old pinout and 1.0

Something like this could be implemented with logic converters between the connection points. This could also leads in some other interesting directions as well:
  • Being able to select/designate individual pins as 5v or 3.3v logic
  • Integrating dynamic pin assignment so the pinout could be adaptable to older shields configurations
  • And if you really wanted to get crazy, you could even wire the whole thing up to be driven by an integrated IC so you just add a library to your sketch and assign the pinout and voltage in software.
  • And since I've already gone way out in left field, to complete the prefect conversion shield, add either an IC to linearly scale the analog inputs or a separate 5v 12 or 16 bit ADC

EDIT: Just read the post about the GTL2000 and it got me thinking there has got to be a chip that could route pins and shift logic levels... Yup.

6  Using Arduino / Project Guidance / Re: IRDA Stack on: November 26, 2012, 12:19:50 am
Hey looking for this exact library for a project of mine, any luck with it? Sounds like you were close as of this post.
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