Since there are numerous existent Arduino shields with 5V signal levels, versus the 3.3V level at which the Arduino Due runs, users would need to have some solution to maintain interfacing compatibility.
This in-between shield would be inserted first into the Due, and on top of the shield would be inserted any arbitrary existent Arduino shield.
To allow separation for routing between the 5V shield lines and the 3.3V Due lines via the level translators, the in-between shield could have either slightly offset headers&sockets, or else surface mount headers on the bottom.
In contrast to resistor/diode-based methods, the above level-translator IC based solution should work bi-directionally, for all signal types (digital I/O, PWM, analog lines, Serial, SPI, I2C), and thus for all shields.
Any thoughts or issues seen regarding this Adapter-Shield approach?
Perhaps someone (or the Arduino dev team) can design a shield like the above.
Please provide your invaluable contribution when you have something more interesting to say.
If you don't like Arduino Due nobody is forcing you to be on this forum.
Saying "dumb" doesn't contribute to the discussion.
@CrossRoads:
Looking good -- That layout image of yours is just to show the orientation and not the actual level translation itself, yes? Have you looked into the GTL2000... or the TXB0108 would work too, although I believe the GTL2000 is significantly cheaper.
Yes, it was just to get the headers defined, to show that 2 sets of headers could be made to fit next to each other - males down to the Due, and females up to shields.
I think I'll slide the 2nd set over some more to make room for signals to be buffered in the middle area and then go back out, especially in the double row area.
Are there many mega shields? Maybe just drop that area and make sure the 20 Uno IO + power + ICSP headers are supported. Need to beef up the power traces.
Crossroads
(with the system calling me "derekmjenkins" for some reason - hopefully just a test towards solving my week day log in problems)
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.
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.
I was thinking just TXB0108s or maybe a couple of GTL2000 for the bank of 18 header pins.
Bring the analog straight over, with TXB0108 in parallel, maybe a jumper to enable the OE/ when digital was required.
Or couple TXB0104s so analog/digital could be split up some.
Really stinks not being able to log in during the day except occasionally due to system conflicts or something.
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.
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.
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.
Here's the schematic & layout, please create a version with the parts you are suggesting.
Top & bottom mount surface mount headers would be one way to keep the physical board the same size, as long as its cut back from the USB header.
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.