ATMEL Mega1284P evaluation board avalible

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?

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.

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.

mowcius:

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.

Well it's providing multiple options :)

Well, for me at least, the DIP version allows you to keep the board in case you fry the processor. I'm not good at soldering, and processors do go bad once in a while. In terms of investment and considering most people are not great with soldering SMDs, this is quite logical. Also, in case you want to use the board for a standalone project, you may use a (not so much) cheaper chip (ATmega32, 16, 644p). So for tinkering and prototyping, nothing beats the DIP version.

Didn't the first design use the surface mount ATmega1248p? :\

Also, why not use an RTC with integrated crystal? Something like this... http://www.maxim-ic.com/datasheet/index.mvp/id/4627

Last but not least, are you taking orders?

RTCs with integrated crystals are expensive. Have you looked at how much the DS3231 is?

~$10...

No, I haven't... :| I had a look at Maxim's website... but for that price, the DS1307 is the way to go. The integrated crystal isn't worth the 8 or 7 extra bucks! :S

I got a couple as free samples when I wanted some and I have to say that they are brilliant RTCs but very expensive for small prototype runs.

Guys,

Some humble thoughts of mine.

  • Use a smaller foot print 3V3 regulator like SOT-23 to save space. For example MCP1700T. By doing this, you can replace the bulky capacitor using a small 0603 1uF 16V ceramic capacitor.
  • Keep the uSD connector only. SD card is pretty hard to find nowadays and slightly expensive. If you look through Nathan's post on trip to Shenzhen, you'll know what I mean.
  • Instead of adding a dedicated RTC chip, a 32 kHz can be used to drive TIMER2 on PC6 & PC7. RTC without any extra cost.

Would love to see the outcome of this thread. :)

a 32 kHz can be used to drive TIMER2 on PC6 & PC7. RTC without any extra cost.

True, but you loose two pins and a timer and may have to write RTC code. I guess it depends on whether you just need to know how many mS since you went to sleep or need to know the actual time.

I'm not a big fan of the 1307 (I prefer the DS3234/3231 because they are more accurate) but it does the job well enough and is half the size of the TCXO chips.

@Crossroads, do you have the SQW signal going to an interrupt pin so you can create a version of millis() that doesn't skip a beat or have the RTC wake the processor at 3AM.

Would love to see the outcome of this thread.

Wouldn't we all. The pressure's on Crossroads :)


Rob

do you have the SQW signal going to an interrupt pin so you can create a version of millis() that doesn't skip a beat or have the RTC wake the processor at 3AM.

Somehow I don't think he's connected anything up yet.

You guys might want to consider RX-8025 as the RTC. Comes with a built-in crystal. Price is slightly more than DS1307.

Yeah but it's not a common device. I think I'd rather have a DS1307 (with external crystal).

Actually my idea for the ATmega1284p would be to use the oscillator pins for the RTC built by software.

Providing a place for the crystal and leaving the pins open to a connector would be good enough. It's something that if I remember correctly isn't possible in the Arduino Mega. :\

An advantage of RTC is that it remembers the date/time when power (except for coin battery to RTC) is off. It was stated earlier that knowing the date/time is often important or desirable for logging things to the proposed memory card.

bubulindo: Well, for me at least, the DIP version allows you to keep the board in case you fry the processor. I'm not good at soldering, and processors do go bad once in a while. In terms of investment and considering most people are not great with soldering SMDs, this is quite logical.

Well this last bit was my point. One of those chips is extremely fine pitch. I have a similar project and the stencil just came in. I'm pretty nervous about being able to assemble it with a stencil and an oven, never mind hand soldering. Although, there is no reason it can't be sold assembled with a socket. Realistically, as a mostly SMT device, i doubt too many people would buy it as a kit. But you never know.

Graynomad: 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

The method the standard arduino uses with 1K resistors in series with the rec & tx pins works pretty well.

Lefty

So I have these for changes:

"The 32kHz xtal, is that really an HC49 case, normally they are the watch crystal style." I will check this, I copied the ATmega footprint, smaller would certainly fit.

"The battery holder will probably clash with the headers and dip socket. " I wil move this left to not have the base overlap any pins that go thru the board. How do I get the battery markings on the bottom of the board?

"Are the mounting holes at good spacing, .1" preferably but at least whole mm." Not sure what you are asking here.

"what's the advantage of the mpu being DIP? Why would anyone want to switch from the 1284P to the 644P? " The socket can handle any of the 40 pin DIPs: ATmega164A/164PA/324A/324PA/644A/644PA/1284/1284P I can make SMD version also once I finish the accessory electrical tweaks.

"3.3V regulator & cap" any other inputs on this? It is only supplying current for the SD/uSD.

"uSD connector only" I like the option of either one. Looks like there are plenty of options for brands & sizes: http://www.amazon.com/s/?ie=UTF8&keywords=64gb+sd+card&tag=googhydr-20&index=aps&hvadid=3806787621&ref=pd_sl_3v9txqilg_b

"SQW signal going to an interrupt pin so you can create a version of millis() that doesn't skip a beat or have the RTC wake the processor at 3AM. " I think I can do that - does it need to a hardware interrupt like INT2 on pin PB2, or can it be a PCINT like PD7?

"The pressure's on Crossroads" No pressure, I am having fun solving this puzzle.

"Somehow I don't think he's connected anything up yet." Not true - board as shown is all routed. I just rip up small areas and make tweaks as I go.

Real time clock - is any one familiar with this Pericom part: PT7C4311WEX Digikey has them for 85 cents in qty 1, having some trouble locating the datasheet for it.

"One of those chips is extremely fine pitch. I have a similar project and the stencil just came in. I'm pretty nervous about being able to assemble it with a stencil and an oven, never mind hand soldering."

The FTDI chip is really nice for USB. I think that is the only part I'd be uncomfortable hand soldering, the 0805 size Rs, Cs, LEDs look do-able.

RTC - I am using pcf8563T (smd), 5xcheeper than the ds1307, and only needs 200nA current (you need two additional diodes for the pcf) Battery - I've moved to 12mm diameter cell recently (cr1220), there are nice sockets available, it will last many years as well.. No need for such giant hockey puck :)

How do I get the battery markings on the bottom of the board?

Don't know, I don't use Eagle for anything but viewing other people's files.

"Are the mounting holes at good spacing, .1" preferably but at least whole mm." Not sure what you are asking here.

Just that the distances between mounting shouldn't be something like 57.356mm that's hard to measure with you come to mounting it in a box.

"SQW signal going to an interrupt pin so you can create a version of millis() that doesn't skip a beat or have the RTC wake the processor at 3AM. " I think I can do that - does it need to a hardware interrupt like INT2 on pin PB2, or can it be a PCINT like PD7?

Either way, I would probably save the INTs and use a PCI, but INT2 would be a bit easier to use from the software point of view and it's "spare" according to the Arduino or do the 1284 core files handle attachInterrupt(2,xx).

"3.3V regulator & cap"

The MCP1700T is good, @ 250mA it will handle the power I would think, what power do the SD cards draw? The SOT23 has a tempco of up to 336 C/W and the the SOT89 only 52 C/W. So the SOT23 can only handle about 1/3W at room temp (depending on how much copper it has around it).

is any one familiar with this Pericom part: PT7C4311WEX

Not me,it looks similar to the 1307 but I don't see any benefit to using it. The RX-8025 mentioned before looks nice and I do like the built-in TCXO, but if you went that route I'd go with the DS3231 chip. There are libraries for the common chips, probably not for the others, so unless there's a really neat feature not available on the 1307/3231 I'd stick with them.

One of those chips is extremely fine pitch.

I use a hot air gun to solder these (the FTDI is the finest I've done so far), easy, just run two beads of paste along the pads and hit it with the hot air. Clean any bridges with solder wick.


Rob