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Author Topic: board running at 16MHz with 3.3V ?  (Read 5466 times)
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Lille - France
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Hi

I've looked at the many arduino boards, but i always see boards running at 3.3V with clock at 8Mhz
or boards running at 5V with clock at 16Mhz

Do you know if it's possible to have a board with 3.3V / clock 16MHz ?

The fact is i have devices that use 3.3V, so this voltage perfectly fits my need, but I also use NewSoftSerial which requires clock at 16Mhz, and the developer of this lib says it's hardly impossible to make it work with a 8 MHz clock...

Any idea about such a board 3.3V / 16 MHz ?

Thanks
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The Seeeduino board runs @ 16MHz with 3.3V

http://www.nkcelectronics.com/seeeduino-fully-assembled--arduino-compatible.html
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Lille - France
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Cool !

And does it exist a mini seeduino equivalent to the arduino Pro mini ?

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Not yet, but I am sure Seeedstudio is reading your request right now...
Or you could take the Arduino Pro mini 5V - 16MHz and supply 3.3V, like Seeeduino does (bypassing the integrated voltage regulator)
« Last Edit: March 13, 2009, 02:46:32 pm by nkcelectronics » Logged

Lille - France
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Ohh if Seeedstudio wants to know my need, here it is smiley

And i think my need is the need of many persons:

Aim is to have the smallest piece of arduino compatible (like the Pro mini) with clock at 16MHz to have NewSoftSerial, with the smallest power needed (3.3V) and the smallest piece of xbee connected to it easily

Or even better, to have the smallest piece of arduino capable of 2 uarts, 1 isn't really enough

Some kind of a sanguino mini pro in fact (644p is quite interesting compared to a 328p)

And of course with having the lowest energy consumption in order, in the long run, to have a wireless small piece that can send small amount of data from time to time for years

By the way I've seen in your shop http://www.nkcelectronics.com/xbee-shield-remixed.html, it's surely what i'm looking for...
But this shield needs 3.3V or 5V ?

Because i've bought Xbee module from libellium but this shield is sooo big, I really don't understand why... (it connects on 5V provided by ICSP)

Cheers
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Operating the chip at 16 MHz with 3.3 volts is beyond the specified maximum frequency "Safe Operating Area" for the mega168 chip.

Please take a look at the charts in section 26.3, figure 26-2 "Maximum Frequency vs. Vcc, ATmega48/88/168", which appears on page 304 of the latest version of the datasheet:

http://www.atmel.com/dyn/resources/prod_documents/doc2545.pdf

There is a linear line between 10 MHz at 2.7 volts, and 20 MHz at 4.5 volts, which is a slope of 5.56 MHz/volt.  So at 3.3 volts, the highest frequency within the "Safe Operating Area" would be 13.34 MHz.  At that slope, 3.78 volts it the point where 16 MHz is within the "Safe Operating Area".

At 3.3 volts, 16 MHz is essentially overclocking the chip by 20%.  Many chips probably do run just fine that way, at room temperature, and if the 3.3 volts is accurately regulated (likewise, many PCs run fine when substantially overclocked).  But it is still running the chip beyond the maximum "Safe Operating Area" specified in the datasheet.  A good engineering practice would be to consider the tolerance of the voltage regulator and use a clock frequency within the safe operating area at the lowest possible voltage the regulator might output.

Perhaps Seeeduino rigorously tests the overclocking ability of every board?  Somehow I doubt that.
« Last Edit: March 13, 2009, 03:12:46 pm by pjrc » Logged

Lille - France
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Thanks Paul for those technical information !

In fact, I was wrong in my summary, I've told never NewSoftSerial would support 8Mhz, which is completely false.

This feature is possible and is in the roadmap of the team

I've been mistaken with another thing the lib shouldn't be able to do, that is support for asynchonous multiple objetcs
More info here : http://sundial.org/arduino/index.php/newsoftserial/

So as a conclusion, be patient and use NewSoftSerial with arduino pro mini 3.3V / 8MHz

Now looking for the smallest xbee shield working with 3.3V...

Thanks
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@enzo, if you need a small footprint for XBee + Arduino, then take a look at the Funnel IO http://www.nkcelectronics.com/funnel-io-remixed.html

It runs at 8MHz, but maybe form factor is more important than speed?  Are you sure you need 16MHz?
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Lille - France
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Ah yes, very interesting this board !

I need now 16MHz in order to be able to use NewSoftSerial
But as I said previously, this lib should work at 8MHz in a near future

I'm just waiting for such a good feature

Thanks for the link NKC
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Read this quote from this thread (2nd page, 5th post):
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1236337068

Quote
FWIW, I've been running the ATmega168 at 3.3V with a 16 MHz resonator on about a dozen units with no ill effects whatsoever. Same reason as crashingdutchman, i.e. to connect a radio module which doesn't tolerate 5V.

So far, all my boards work just fine, at room temperature anyway... One of the units has been running continuously for over two months now.
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Lots of people overclock the PCs too, without any problems.  Many have done the mods in the winter and had them work flawlessly until the summer.

Running for 2 months at 3.3 volts regulated and room temperature wouldn't be nearly as good a test as running at 3.0 volts and 50 deg C for even 15 minutes.  If you can do that, then you know your chip has some margin.  If it fails the moment you go under 3.2 volts or raise the temperature a bit, then you know you're running right near the limit.
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EDIT - a recent comment says they are running outside of the envelope, so I guess it is not uncommon (but I will have to try it next summer around Yuma AZ).

Sparkfun has a new "OpenLog", and according to them (in the comments on the product page), there has been some kind of stepping or revision that allows 3.3v and 16MHz.  I can't find any confirmation of this.  (Of course Atmel is sometimes slow - Digikey has TSSOP8 ATtiny45s but Atmel doesn't show anything on their site).
« Last Edit: January 08, 2010, 02:15:57 pm by tz » Logged

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Quote
I've been running the ATmega168 at 3.3V with a 16 MHz resonator on about a dozen units with no ill effects whatsoever.

So the manufacturers who design this system deliberately say it will only run at a slower speed for what advantage?

Precisely none.

If a device is capable of reliably running faster then it would say so in the data sheet and the manufactures would have a better device.
It can't, so they don't say it can. Any one who thinks he knows better that the manufacturer and designer of a device is fooling himself and possibly other gullible people.
Get a grip.
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I should get some liquid nitrogen and a 32Mhz resonator...

Chips tend to age and have problems at higher temperatures.  A particular batch that is tested is only guaranteed to work inside the envelope - but there may be many "golden" units that can operate far outside.

If I remember right, the big CPUs are just rated - if it works at 2Ghz, it gets a 2Ghz label (the test conditions are more strenuous to guarantee it for the life of the chip).  If it doesn't, they test at 1.8, then 1.6 and so on.

You want your car and its electronics like the radio to work when you start it in the hot sun.  Most are rated to 85C or even higher (and down to -40 - note that around -35C many electrolytics freeze and lose their capacitance - another problem).

It depends what it is for.  If it is not going to be outside of room temperatures it will probably work.  But I wouldn't count on it for "general purpose" because that can be under much different conditions.
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The Jeenodes are basically using the atmega328 3.3V at 16MHz.
I have used the nodes in a sensor network for my home and I didn't see any loss in performance or data. I also have an outdoor temperature sensor and didn't give me any problem (yet).
As the author says:
Quote
Using an ATmega168/328 at 16 MHz with 3.3V exceeds the specs by some 2.7 MHz - but it works just fine.
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