Suggestions about Mega-equivalent with built-in Ethernet

I'm just about to go to production with a Mega version of the EtherTen (http://www.freetronics.com/etherten), but it's not too late to make last-minute changes so I'd be very interested in any suggestions. It does everything the EtherTen does (including Power-over-Ethernet, microSD slot, etc) but with more I/O and an ATmega2560 MCU. It also has a small prototyping area which should be handy for single-board sensor / control projects, and I've specifically broken out the I2C connections next to the proto area.

There are still a couple of airwires and some minor pushing and shoving to do, but it's getting quite close:

Obviously it still needs header labels etc sorted out.

Yes, the microSD slot is in a very strange location (right in the middle of the board) but I couldn't figure anywhere better to put it. The Mega has headers and other connectors all the way around the perimeter, so there's just nowhere to put it that overlaps an edge. Hopefully it won't be too much of a pain.

So, any wishlist items or suggestions before I crank out the Gerbers and start production?

Jonathan Oxer Practical Arduino: www.practicalarduino.com

Silk says 7-10V DC, shouldn't that be 7-20V?

shouldn't that be 7-20V?

No, that's deliberate. The combo of the pair of MCUs and the Wiznet Ethernet chipset draws a significant amount of current, and supplying anything more than about 12V to the onboard linear regulator can push it closer to the thermal limit than I like: particularly if you stack another shield on top that draws lots of current, such as an LCD shield with a backlight. A combination of boards like an Uno with an Arduino Ethernet Shield and an LCD shield has the same problem. If you feed it 10V it'll be quite happy. At 12V the reg gets very warm, and at 20V it would almost certainly go into thermal shutdown.

You can feed it more, but the 7-10V range indicated on the overlay is a recommendation that gives a bit of a safety margin.

Jon

Why not connecting it with the external memory bus?

Nice routing, Jon! I'm sure that was a ton of work.

I might be totally wrong about this, but I have seen PCBs with a vRestrict area under crystals because a via under a crystal will be in contact with the crystal's metal case. There is a via under one of your crystals (connected to GND I believe?). Just thought I'd mention it in case it was not intentional.

@bubulindo:

Why not connecting it with the external memory bus?

I don't understand. What external memory bus? Care to elaborate?

@nootropic:

There is a via under one of your crystals (connected to GND I believe?). Just thought I'd mention it in case it was not intentional.

That's a very good point, you're right that it's something to be careful of. In this case it's OK because as you point out it's a GND connection, so it doesn't matter if it shorts against the crystal case. The plan with production of this PCB is to have all the vias "tented" (covered with soldermask) but even with tenting it's a good idea to not put vias where they could short out. A via under tenting is still a structural weak point for the soldermask and there's the danger of the connection being exposed.

In any case that particular part of the PCB is being shoved sideways a bit to make room to route those last few airwires!

Jon

IMHO, why not go for switch mode regulator? After all the boards is going to use quite an amount of current. Furthermore, the overall board cost is already high, adding a few more dollar for switch mode IC, inductor, diode and some capacitor won’t cause any harm. Then you can pump in higher voltage and definitely less heat! :slight_smile:

Guessing he means connect the ethernet feature via address/data port A (D22-29) with D39 ALE, D40 Rd, D41 Wr, rather than using the SPI port. I don’t know if there’s any existing Arduino ethernet kits that do this. Using SPI means compatibility with existing ethernet shields and EtherTen.
Or have I misunderstood what bubulindo was suggesting?

Suggest making the proto area 2 pins longer, to accept at least 1 20-pin DIP.

48X24X48X: IMHO, why not go for switch mode regulator? After all the boards is going to use quite an amount of current. Furthermore, the overall board cost is already high, adding a few more dollar for switch mode IC, inductor, diode and some capacitor won't cause any harm. Then you can pump in higher voltage and definitely less heat! :)

I'd like to be able to work with up to 14V. Not sure how you'd go fitting the extra components while minimising distance between the reg, diode and inductor. Perhaps by turning the 5v regulator around and moving the 5v cap above the Vin cap?

CrossRoads: Suggest making the proto area 2 pins longer, to accept at least 1 20-pin DIP.

Bottom 2 rows might be feasible. Also, are the Pwr and D13 LEDs different colours?

swordfishBob: I'd like to be able to work with up to 14V. Not sure how you'd go fitting the extra components while minimising distance between the reg, diode and inductor. Perhaps by turning the 5v regulator around and moving the 5v cap above the Vin cap?

I guess once you use a switch mode IC, the e-cap can be removed and replaced with ceramic which are smaller. And for rating around 1A, the package are usually very small (DFN, MSOP, Thin-SOT) for the switch mode and inductor (have to be rated higher current). Maybe it's just me, I'm a fan of switch mode! :)

swordfishBob: [quote author=Jonathan Oxer link=topic=67714.msg498419#msg498419 date=1311804407] @bubulindo:

Why not connecting it with the external memory bus?

I don't understand. What external memory bus? Care to elaborate?

Guessing he means connect the ethernet feature via address/data port A (D22-29) with D39 ALE, D40 Rd, D41 Wr, rather than using the SPI port. I don't know if there's any existing Arduino ethernet kits that do this. Using SPI means compatibility with existing ethernet shields and EtherTen. Or have I misunderstood what bubulindo was suggesting? [/quote]

Yes, that was exactly it. Plus an interrupt connection from the W5100 to the ATmega so you wouldn't have to poll the chip to know if someone was connected there. The reason for that is that with a big memory chip like the 1280 or 2560, there is a lot more space to put in a webpage and act as a server and not a client. Although I believe that this is also in the Ethernet shields so should be here too.

Although the current library wouldn't work, I remember seeing the application note from Wiznet and the code they had (which is used in the library) was prepared to handle both interface situations. This would add bulk to the board as you would need a latch and a lot more vias going around, so you wouldn't have such a compact PCB as you do now.

Also, have a look and see if it's possible to place two connections on the TOSC pins in the chip. That way you could place a 32,768kHz crystal and run a clock in software on the board. Since this is most likely to be used connected to the internet at almost all times, you wouldn't need an external RTC and just have a crystal to keep time and synchronize time from the internet.

Suggest making the proto area 2 pins longer, to accept at least 1 20-pin DIP.

That's going to be hard but I'll see if I can squash in a couple more.

have a look and see if it's possible to place two connections on the TOSC pins in the chip.

Cool idea. I wouldn't populate it by default, but watch crystals are tiny so I should be able to bring out a couple of pads to solder the flying leads onto. I'll give that a go.

are the Pwr and D13 LEDs different colours?

Yes, blue for power and red for D13, same as on the EtherTen.

Jon

why not go for switch mode regulator?

I'd love to do that. Our assembler is currently checking availability and price on a couple of parts, including the EUP3410 and EUP3452A on this page: http://www.eutechmicro.com/PL_9_11_EN.html

If it turns out I can go switchmode for a minimal impact on BOM cost (and it fits!) I'll do it.

Jon

[quote author=Jonathan Oxer link=topic=67714.msg498892#msg498892 date=1311859749]

why not go for switch mode regulator?

I'd love to do that. Our assembler is currently checking availability and price on a couple of parts, including the EUP3410 and EUP3452A on this page: http://www.eutechmicro.com/PL_9_11_EN.html

If it turns out I can go switchmode for a minimal impact on BOM cost (and it fits!) I'll do it.

Jon [/quote]

Those 2 are running at around 300 kHz. You reduce the inductor size if it's higher, something like 1-2 MHz. You might want to check on the WizNet chip on any frequency range to avoid.

[quote author=Jonathan Oxer link=topic=67714.msg498890#msg498890 date=1311859557] Cool idea. I wouldn't populate it by default, but watch crystals are tiny so I should be able to bring out a couple of pads to solder the flying leads onto. I'll give that a go. [/quote]

Yes, I'm halfway (stopped) through designing a board with the external memory bus, and that was one of the things I thought to be able to have time without much fuss with external components.

Having a switched power supply sounds good to me too. At how much would this be selling?

bubulindo: Yes, that was exactly it. Plus an interrupt connection from the W5100 to the ATmega so you wouldn't have to poll the chip to know if someone was connected there. The reason for that is that with a big memory chip like the 1280 or 2560, there is a lot more space to put in a webpage and act as a server and not a client. Although I believe that this is also in the Ethernet shields so should be here too. ... This would add bulk to the board as you would need a latch and a lot more vias going around, so you wouldn't have such a compact PCB as you do now. .

I can understand someone wanting this (and so many other add-ons seem to compete for SPI). However, my priorities would be fitting with the Mega dimensions, having the proto area, and compatibility with existing library.

However, my priorities would be fitting with the Mega dimensions, having the proto area, and compatibility with existing library.

That was exactly my thinking. What I wanted was a board that's like a Mega, an Ethernet shield, and a (small) proto shield all squashed into one as a drop-in 100% compatible replacement.

I'm still interested in ideas that deviate from that though, because there could be other specialised versions to follow if there's enough interest.

Jon

If it turns out I can go switchmode for a minimal impact on BOM cost (and it fits!) I'll do it.

I did a similar design with a land pattern that could accommodate either a SOT223 or a TSR-1 switching reg.

The idea was to allow loading of one or the other according to requirements. The TSR series from Traco can handle 1A with no heatsinking. I gather that DPAK is the main regulator, the pinouts may be compatible or this would allow the use of a SOT223 as it would only be used for lower power application. Either that or just use the TSR to make life simpler.

two connections on the TOSC pins in the chip.

I did this as well, however I had solder bridges to isolate those two IO pins ("after" the XTAL) because I figured with shields attached there would be a high capacitance on the traces due to the long runs/headers/etc.

What external memory bus? Care to elaborate?

The 2560 is capable of using external memory chips, you could add say 1Mb of data memory (in 64k pages). This can still be done on a shield though. In my design I added a RAM chip and a few page-select signals plus battery backup. But I didn't lose space to Ethernet so had the real estate.

ALso, do you have a jumper to break the auto reset feature?


Rob