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Wiring 2.0 Hardware (Read 36882 times)
11/03/10 at 18:33:01

bhagman   Offline
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Hi!

My name is Brett Hagman and I will be working on the next hardware design for Wiring.  I have discussed with Hernando all of the ideas of developing a cheaper, smaller Wiring board.

I wanted to start a discussion on what things people would like to see on the hardware board.

So, this thread is an open discussion for the next Wiring board design.

Here are a few things I would like to add to the new design:

1) MCU: I'd like to make several options (maybe different boards)
  • ATmega1281, ATmega2561, ATmega640, ATmega1280, ATmega2560 (all pin compatible - 64 pin package)
  • ATmega644P/ATmega1284P (44 pin package)


2) Make the FT232RL optional - besides cost savings, there are power savings, and you can utilize the pins for the hardware serial for other purposes (alternate hardware capabilities).  Regardless of the FT232RL, a header break-out for an FTDI USB to serial cable (or something similar).

3) Board size - I'd like to go for 3 inches by 2 inches.

4) Power regulator/external power - minimum of 1 amp regulated 5 volts - debating whether we should use a buck/boost regulator, or just a plain ol' 7805.

5) Use a switch for the USB/External power selection.

6) Footprints for both USB B and USB mini-B 5-pin jacks.

Please feel free to add to this thread, any comments/suggestions for the next hardware design.

b
« Last Edit: 11/09/10 at 22:51:03 by bhagman »  
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Reply #1 - 11/04/10 at 06:06:53

Zap   Offline
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Yes I like all the suggestions, as for
2: yes make it optional, I use my own max232 cct with auto reset for uploading and most standalone projects don't need the extra cost of USB.
4: They are many switchmode regs now available in the To-220 (with HS) footprint, so the user could either depending on cost and efficiency required. (just allow for the slightly bigger PCB footprint)
5: Use a three pin header with jumper strap.

Zap
 

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Reply #2 - 11/04/10 at 15:02:31

roypardi   Offline
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Hi, I'm not that hardware savvy so don't have much to contribute. I've used the 1st gen Wiring boards for many projects and they have served very well.

2.) FTDI cable. I use the Boarduino with an FTDI cable and it works fine. If this saves on cost/frees up pins that would be a plus.

5.) The existing jumper is fine (how often does one need to change this, etc.). My issue is with the fuses - I seem to have blown the fuse on both my 1st gen Wiring boards so I can't use USB power at all. Is there a design issue with the fuse?

My particular usability concerns:

a. Is the overloaded pin functionality due to the chip or the board design? (e.g. pins 2/3 are hardware serial and interrupts). If it is board design then eliminating this overloading would add greater functionality (e.g. accessing all 8 interrupt pins while also using hardware serial).

b. use screw terminals instead of pins ...  Wink  I know a change is not likely but after many projects, the hardest, most error prone aspect of using the Wiring board is cabling up - making cables w/ a hand crimper, header blocks slipping off, etc.
 
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Reply #3 - 11/09/10 at 22:49:43

bhagman   Offline
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Unfortunately the "overloaded pin functionality" (Atmel calls them "Alternate Pin Functions" - bug/feature... your call) is part of the chip design.  Not much we can do about that.  ([sarcasm]Yeah, I'm particularly fond of the INTx interrupts on the hardware serial pins[/sarcasm]).

RE: screw terminals - it's already in the works to make the headers holes spaced from the edge of the board to accommodate 0.1" spaced screw-downs.

Anyone have any comments on the board size?  GET YOUR RULERS OUT! Smiley

b
 
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Reply #4 - 11/10/10 at 20:26:31

mowcius   Offline
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Just to comment, had a quick chat to Brett. Someone mis-read  Tongue USB mini B is definitely staying (thankfully) so +1 for both sets of pads.
I like the USB B as it's definitely much less easy to damage. I am always careful with things but the USB B ports, they feel as if you can plug them in and out with no worry. USB mini B is a bit more delicate and somehow I seem to have broken one (but I think it may have been a slightly duff socket to begin with).

Board size sounds good. - Arduino is... well we won't go into the random arduino board sizing but it's roughly that.
Should give a good amount of space for all the pins and other components.

I would probably stick to simply a 7805 but pads to allow other regulators/boost converters as people always seem to like using 9V batteries - with a boost converter they could go with something more sensible!
If a nice regulator/boost combo can be purchased without too much in the way of price increase then I'd go with that. Not sure how expensive they are as a combo.

Quote:
b. use screw terminals instead of pins ...

Not convinced by this, Perhaps a different 'ruggedised' board with these and a bit of protection for things. I dislike screw terminals most of the time. I only use them for things like motors and larger stuff. Tiny multi strand wires are terrible in screw terminals.

Mowcius
 

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Reply #5 - 11/11/10 at 03:20:00

bhagman   Offline
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RE: Regulator - the biggest problems with using a buck/boost regulator are the cost and the real estate taken up by the other components for the switcher (i.e. inductor, mostly).  I'm leaning towards an LDO linear regulator.

RE: Screw-downs/screw-terminals - This will only be an option.  i.e. the screw-down terminals can be added by the end-user.


Back on the subject of regulators, if we don't have the FT242RL on board, we will need a 3V3 regulator.  My thought is to just have a 3V3 regulator, regardless.  A 250mA LDO should do the trick.

Also, I was thinking of this:

1) Standard 2.1mm Jack, with protection diode.
2) 2 pin header (JST?) for battery connection (i.e. 6V or better) bypassing the protection diode.

This way you can run the board by supplying 6V via the battery connector to a LM1084 (or similar) and you can get 2A output.

Though, a buck/boost would be nice to put on there.  Then you could also run the board from 4.5V (or even 3.0V!) if you want.  Kind of a tough call.  I think the linear regulator will be a better choice in the long run.  (Can make an external boost regulator board to apply to the 5V input maybe?)

Thoughts?

b
 
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Reply #6 - 11/11/10 at 09:30:38

mowcius   Offline
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Quote:
Regulator - the biggest problems with using a buck/boost regulator are the cost and the real estate taken up by the other components for the switcher (i.e. inductor, mostly).  I'm leaning towards an LDO linear regulator.

Yeah but as presumably it would be onboard when you buy it you could make it some tiny surface mount components.

Doing it all surface mount, you could fit it all into the space of a typical cheapo 7805.

Quote:
we will need a 3V3 regulator.  My thought is to just have a 3V3 regulator, regardless.  A 250mA LDO should do the trick.

250mA sounds fine. Again it can be something tiny.

Not sure I'd go with 2A, seems a bit ott, I would have thought 1A would be plenty although I may be wrong, what's the price difference?

Mowcius
 

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Reply #7 - 11/11/10 at 16:38:55

bhagman   Offline
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mowcius wrote on 11/11/10 at 09:30:38:
Yeah but as presumably it would be onboard when you buy it you could make it some tiny surface mount components.

Doing it all surface mount, you could fit it all into the space of a typical cheapo 7805.

... well, not for running at 5V @ 2A+.  The coil is the problem.  This point is moot, though, since we aren't that hard-up for space.

After looking into it some more, I think the cost is actually going to be the prohibiting factor (~$5 per switcher @ 100Qty, and that doesn't include the other components - ~$1 for 2-6A rated coil).  If anyone has a good reference design/line on parts that could sway me to go with the switcher, let me know.

The 2 amps I was referring to in the last post is the maximum that the 1084 regulator would provide @ 6V input.  The 1084 can provide up to 5A regulated (@ above 6.5V).

So I am thinking this:

Just go with the "good ol'" 7805 @ 1A (nice and cheap).  The 1084 is still more expensive (almost $3 @ 100Qty), nice LDO and all, but the benefits don't outweigh the costs.

Thoughts?

b
 
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Reply #8 - 12/09/10 at 19:21:47

bhagman   Offline
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So, decisions are below:

New board name: Wiring S (ATmega324P/644P/1284P based)
5.0V Regulator: 7805 or similar, min 2V drop-out, min 500 mA
3.3V Regulator: LP2992 or similar, min 200 mA
FT232RL USB optional
FTDI USB to Serial cable compatible header as option to USB
USB B Connector only

If you have anything to add, do it soon.

b


 
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Reply #9 - 12/09/10 at 19:49:57

mowcius   Offline
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Quote:
USB B Connector only

Can't you add the pads for the mini B connector then?

I'd have thought you might as well as it aint gonna cost any more Cheesy
 

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Reply #10 - 12/09/10 at 20:42:14

bhagman   Offline
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2 thoughts:

1) As you've mentioned before, and I have to agree, the mini B connector is not nearly as durable as the standard B connector.

2) Unless there is an overwhelming amount of support for the mini B, there is no reason to have an option for the mini B on the board, since producing a different board with only a different connector just makes production more complex.

Convince me otherwise Smiley

b
 
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Reply #11 - 12/09/10 at 21:54:33

mowcius   Offline
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As I had forgotten about the 'other' header I am happy with the USB B only owing to the complex nature of trying to fit both in.

I personally don't like mini USB B so much as I have managed to break one. Never broken a USB B!

Mowcius
 

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Reply #12 - 12/10/10 at 23:33:38

bhagman   Offline
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Ok, schematic complete.  Part placement complete.

Please have a look, review and yell at me if you think something should be changed.

...
Wiring-S-V10-Schematic by Rogue Robotics, on Flickr

...
Wiring-S-V10-FTDI-Option-Various-Headers-2 by Rogue Robotics, on Flickr

...
Wiring-S-V10-FTDI-Option-Various-Headers-1 by Rogue Robotics, on Flickr

...
Wiring-S-V10-Cable-Option-1 by Rogue Robotics, on Flickr

...
Wiring-S-V10-FTDI-Option-1 by Rogue Robotics, on Flickr

b
 
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Reply #13 - 12/11/10 at 09:27:59

mowcius   Offline
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For once, I can't think of anything wrong with that Cheesy

I'm trying to decide if I like that reset switch or not though :p
 

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Reply #14 - 12/11/10 at 23:08:11

mga   Offline
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Is the idea to choose from female, male, screw headers? I notice you use all three in the 3D example. My vote would go for the male. There is convenience when having females to just put the cable in but later it can become a mess when you want to "go pro" with the project.
 
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