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Topic: ATMEL Mega1284P evaluation board avalible (Read 181429 times) previous topic - next topic

retrolefty

Quote
Would moving the auto-voltage switch to a daughter / companion board be a good idea?  That would free some space and reduce the component count for people who intend to run the board from a 5 volt source.


Not as useful as just s@#t canning the whole concept of auto-voltage selection. It's such a lame function that uses way too many components and space for what it brings to the table. Real people should use real switches or jumper clips for things like voltage source or voltage level selection, auto-reset enable/disable, and any other useful user hardware selection feature required or desired. Auto-voltage selection was an idea that might have had the best of intentions for beginners, but if just limits flexibility and has some questionable design points.

OK, I'm done with my arduino rant for the time being.  ;)

Lefty


skyjumper

The automatic selection of powering from USB or another source is very useful for many applications. If the device is going to live somewhere away from a PC ou need to power it, but for the occasional trip to the PC to be updated or whatever it comes in very handy not to have to go searching for the wall art.

skyjumper


No, but you have seemed to have created an itch in a lot of us. I'm still not convinced that all the software hurdles have been leaped over yet, clock @ standard 16Mhz, bootloader compiled to run at 16Mhz, etc. Pin mapping should be the same as 644p however.


I have a bootloader running at 16 MHz and the cores available at avr-developer.com work nicely.

retrolefty

#48
May 17, 2011, 12:07 am Last Edit: May 17, 2011, 12:10 am by retrolefty Reason: 1
Quote
If the device is going to live somewhere away from a PC ou need to power it, but for the occasional trip to the PC to be updated or whatever it comes in very handy not to have to go searching for the wall art.


What I proposed doesn't prevent that, it just requires moving a jumper clip from one position to the next position. What's not handy about that?

Another example of the auto-voltage lameness. Assume your project is powered externally and is independent to a PC. Why power up the FTDI or 8u2 chip? Check out the Seeeduino design for power selection, manual two position switch for usb/external power and FTDI power source is hardwired to the USB connector only. That's good functional design.

Lefty

tastewar

I find it mildly convenient to be able to take my computer over to my running project, hook up my USB cable, upload new code, then disconnect shortly thereafter without the project having to reboot. Would your solution allow that?

retrolefty

#50
May 17, 2011, 12:28 am Last Edit: May 17, 2011, 12:35 am by retrolefty Reason: 1

I find it mildly convenient to be able to take my computer over to my running project, hook up my USB cable, upload new code, then disconnect shortly thereafter without the project having to reboot. Would your solution allow that?


Yes, that would still function as you stated.

As far as power switching, the arduino auto-voltage switching remains powered by the external source if power is on both usb and the external power connector at the same time (external has priority), so that would have no bearing on what you are asking to do, the board would not reboot because you removed the usb connector.

Lefty

tastewar

Cool! In which case, I personally have no need for auto power source switching.

skyjumper

Lefty, i don't follow... It seems like you are saying that a jumper needs to be moved to switch from wall wart to USB power. Or does your jumper switch from auto-switching to not auto-switching?

retrolefty

#53
May 17, 2011, 01:03 am Last Edit: May 17, 2011, 01:10 am by retrolefty Reason: 1

Lefty, i don't follow... It seems like you are saying that a jumper needs to be moved to switch from wall wart to USB power. Or does your jumper switch from auto-switching to not auto-switching?



I proposed eliminating the auto-voltage switching logic altogether. Instead replace with a simple 3 pin SIP male pin header and a two position jumper clip. In one position the boards power is coming from the on-board +5VDC regulator, in the other jumper position the boards power comes from the USB +5vdc source. You decide how you want to power the board and place the jumper appropriately. A two position manual switch could also work just as simple as it does in the Seeeduino board designs. How the board is powered has no bearing on if you are using the usb serial function or not, if the board has power the usb can function period.

Edit: What I proposed is to go back to the design that arduino used with the  Diecimila board.
http://arduino.cc/en/Main/ArduinoBoardDiecimila

Schematic: http://arduino.cc/en/uploads/Main/Arduino-Diecimila-schematic.pdf  Note the power selection jumper in the lower left hand of the drawing.


Lefty

graynomad

#54
May 17, 2011, 07:28 am Last Edit: May 17, 2011, 07:32 am by Graynomad Reason: 1
What lefty is suggesting is (I think) exactly what I have on my two current 1284 designs.

Note the diode on the FTDI chip's RXD line. I'm not 100% sure that's needed but I've had trouble before with this sort of setup where the active chip powered the inactive chip through the IO pin. This is easy to get around by tristating the active chip's output as well but I prefer a hardware option that doesn't require a use to know about this stuff.

This should allow the USB chip to only be powered when USB is available.

@crossroads, this is a board designed for my network and it's pretty specific to that. I won't be competition, not yet anyway :)

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

CrossRoads

Okay, I think this is for updates.
> added Reset switch.
> deleted autopower, added 3-pin jumper field (5V from regulator, 5V from USB).
(user can bring the three pins to a panel mount toggle/rocker if desired, or to bring in external 5V).
> added DS1307 RTC, crystal, pullups for Square wave output, SCL, SDA lines.
> added 20mm coincell battery, on Bottom of the board.
> RS232 remains. 3 pin header with Gnd in middle for easy board-to-board connections, or to offboard DSub connector.
> Both SD & MicroSD remain, up to builder to populate desired socket.
> ICSP header.
> JTAG header.

Question:  How do I get the battery holder markings to show up on the bottom of the board?
And will what I presume is a plastic coin cell battery holder be interfered with by the atmega socket pins ? If so I need to adjust it placement and fix the routing around it.

Any other options/features/requests?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

graynomad

#56
May 17, 2011, 09:18 am Last Edit: May 17, 2011, 09:20 am by Graynomad Reason: 1
Nice, getting a bit full but has a good range of features.

The 32kHz xtal, is that really an HC49 case, normally they are the watch crystal style.

The battery holder will probably clash with the headers and dip socket.

Are the mounting holes at good spacing, .1" preferably but at least whole mm.

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

skyjumper

If everything else on teh board is surface mount, what's the advantage of the mpu being DIP? Why would anyone want to switch from the 1284P to the 644P?

mowcius

I was also going to mention the RTC crystal size.

I think the battery holder would probably be ok depending on what you use. - Might interfere with the headers but I wouldn't have thought it would interfere with the DIP socket as it has a big hole in the middle.
My thinking is that it could go where the caps and RTC are atm as they're surface mount on the other side so could fit in the big space in the middle of that battery holder.
I mean you could go with a CR1220 or something but I don't personally like the smaller battery types as they're harder to get hold of.

Quote
If everything else on teh board is surface mount, what's the advantage of the mpu being DIP? Why would anyone want to switch from the 1284P to the 644P?

We want DIP as you can then simply use the board as a programmer for chips, remove them and stick them somwhere else.

skyjumper

Quote
If everything else on teh board is surface mount, what's the advantage of the mpu being DIP? Why would anyone want to switch from the 1284P to the 644P?

We want DIP as you can then simply use the board as a programmer for chips, remove them and stick them somwhere else.


Okay. But, this board is kind of overkill for that. if you use the SMT mpu you can save a lot of room. Another board could be designed with many fewer parts as a programmer. Not that its a big deal.

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