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Topic: Arduino Due (released Oct 22, 2012) Compatibility (Read 34 times) previous topic - next topic

retrolefty


Note: I'm not a hardware guy so this may be complete crap.
I have been thinking about the "wimpy output pins that ARM chips, even driving a 20ma led will require a switching transistor"
Now I ask myself:
Would it be possible to make a go between kind of like shield that would cater for this shortcoming?
I'm thinking about having a mosfet on all(?) pins in parallel to (in)direct access to the pin via the header. This way you could chose to have a resistive load on the mosfet or (in)direct access to the 3.3 pin.
I'm saying (in)direct because maybe some extra stuff (I wouldn't know what) could allow for switching between mosfet, 3.3V and 5V. With solder paths the headers could be connected to the pin with the desired functionality. (maybe you guys are smart enough to do it automatically)
Maybe not all options (mosfet, 3,3 and 5Volt) are needed for all pins. I think the UNO digital and analog pins are the first to look at. And probably pin 0 and 1 are never used by any shield as it would ruin the USB communication on the UNO. Which makes 16 pins for all options.

Any input from people who know what they are talking about when it deals with electronics?
Best regards
Jantje

PS
For the UNO there is a go between shield that disconnects the pins from the headers and uses solder paths to connect the pins to the headers. This is part of the solution I'm thinking of "http://tronixstuff.wordpress.com/2012/01/18/review-mayhew-labs-go-between-arduino-shield/"
I say mosfet because mosfet have a smaller voltage drop and internal resistance but maybe transistors or anything else is far better. (I really don't claim I know)




I suspect a 'go between shield' board that converted all the ARM pins to active 5 volt signals capable of sinking and sourcing 30+ ma is possible, but how would you switch them from output pins to input pins via sketch mode commands? No, I think that actual hardware arduino projects will now (or soon post DUE release) have take two different paths, one for the 5 volt higher current capable boards and one for the new 3.3 volt lower current world. It will just be cheaper to buy both kinds of boards rather then to expect some kind of 'go between' board to solve the rather drastic electrical different I/O pin capablities between AVR and ARM chip boards.

Lefty 

Graynomad

#56
Oct 06, 2012, 05:48 pm Last Edit: Oct 06, 2012, 05:51 pm by Graynomad Reason: 1
I think so to, plus how do you deal with analog pins? They can be digital IO as well. It gets very tricky.

I suspect that future shield makers will have to accommodate both voltages if they want to be compatible with both types of base board. That's pretty easy to do on a shield because you know what pins you are using for what. Isn't that what the IOREF signal is to be used for?

_____
Rob
Rob Gray aka the GRAYnomad www.robgray.com

retrolefty


I think so to, plus how do you deal with analog pins? They can be digital IO as well. It gets very tricky.

I suspect that future shield makers will have to accommodate both voltages if they want to be compatible with both types of base board. That's pretty easy to do on a shield because you know what pins you are using for what. Isn't that what the IOREF signal is to be used for?

Yes, The voltage applied to the IOREF pin from the controller board will tell the shield board what kind of host Arduino controller board is being mated with. However that is only avalible on the newer Rev3 arduino boards, not the zillions of pre UNO and MEGA rev3 boards. Chaos will be present for some time ahead.  :D

A shield maker might (or will?) have to state if their shield design is Due only, Due and Rev 3 Uno and Rev 3 Mega compatible, or only non-Due board compatible I guess for one to purchase a future shield and be sure it's compatible with what they are using?

Lefty


_____
Rob

bperrybap


Ok, but lets focus a bit. What would be your recommendation to a newbie to the hobby (with little or no electronics or software experiance) as to which would be their best choice to enter the arduino world once the Due is in fact avalible. I vote Uno, you vote ?

Lefty

For a beginner needing shield compatibility yes, an UNO makes sense, but
I might lean a bit more towards a Leonardo as it can do many interesting things with USB
that can't be done with UNO.

That said, I'd guess an absolute beginner probably doesn't need shield compatibility initially,
so a Teensy board might be an even better choice than an Uno.
It's much smaller, a bit cheaper,  has more resources than an UNO.
(more i/o pins, more RAM, more flash),  has native USB capabilities,
and is also breadboard friendly which makes it much easier to play round with than
an UNO.
For little bit more and about the same cost as an UNO, there is Teensy++ which
has 4X the code space, 4X the RAM and more than twice the i/o pins as UNO.

IMHO, Teensy++ solves the code, RAM, and I/O pin issues for most projects.

Teensy boards are also nice because of their size and form factor they can easily move
from a breadboard prototype to a 1 off project as it can easily be squeezed into many
environments that a Arduino factor simply doesn't fit very well.

With respect to the DUE being a solution for
more speed and resources than the UNO, there are other solutions out there already that
may be more cost effective than the DUE that the DUE will have to compete against.
For example, Chipkit boards. The Chipkit UNO32 is about same cost as the Arduino UNO
(nearly half the cost of the DUE)
but it has the CPU power of the DUE with 5V tolerant inputs in the form factor of the UNO.


---- bill


Grumpy_Mike

#59
Oct 06, 2012, 11:45 pm Last Edit: Oct 06, 2012, 11:46 pm by Grumpy_Mike Reason: 1

Maybe I am lacking imagination, but how about some examples?


The Due fits between the things an arduino can't do because of limited speed / memory and the stuff the Raspberry Pi can't do because it is not a real time system.

So some examples:-
1) Driving a decent resolution graphics display. (LDC or OLED)
2) Sound sampling and manipulation
3) Direct video digitization / generation
4) Controlling stepping motors for CNC with look ahead acceleration / deceleration
5) RFID access control with a decent size database and response time.
6) Oscilloscope / logic analyser with decent sample depth.

Add to that the portability remembering the Raspberry Pi takes 700mA to drive.

Now go and write your Due book.  :P

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