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31  Using Arduino / General Electronics / Re: Practical experience operating Consumer ICs outdoors on: August 17, 2011, 09:20:44 pm
No need to go military - many ICs and discretes come in an Industrial temperature grade that is typically qualified* over the range -40 ~ +80C, for not much more cost than commercial grade parts. At low temperature, condensation will likely be your biggest worry. If you can, hermetically seal the main electronics box ("otter box" might work) with a silica gel packet inside just in case.

*This means only that they are not tested/guaranteed to lower temps, not that they will stop working (and it may be the limit of the manufacturer's thermal test chamber, not the part). Personally, I've yet to see an IC fail outright at LOW temperatures, although more 'analog' stuff can and will drift (caps, resistors, crystals, etc. will change in value; timing-sensitive things like RS232 may be out of whack and your sensors may need temperature-specific calibration outside the guaranteed range). One project I did at work (PIC-based wireless sensor network for a railroad application) had to be qualified to -50C. I figured "what the hell" and set the test chamber to minimum (turned out to be -67C) and let it run with some prototypes over a long weekend. I was not able to induce any 'hard' failures, but I did find that the radios outside the chamber would lose sync with the radios inside once they were about 50C apart - guessing the crystal frequencies had drifted apart enough that they were not talking on the same frequency / timeslots anymore. Once the chamber warmed up a bit they would start communicating normally again!
32  Using Arduino / Networking, Protocols, and Devices / Re: WiFly questions on: August 14, 2011, 12:04:11 pm
It would be nice to just be able to use this nice off-the-shelf hardware with custom FW, but man, $2500 would buy a lot of generic ARM and WiFi chips, plus Bed Bath & Beyond's finest reflow toaster. Are there any WiFi transceiver ICs that are a) buyable off-the-shelf (hobby quantities, no NDA required), and b) have public datasheets (or well-enough reverse engineered by e.g. Linux driver hackers to be useful)?
33  Using Arduino / Programming Questions / Re: Silly "= vs. == in a conditional statement" question on: August 14, 2011, 11:47:41 am
Thanks everyone!

@kerthyn: Seconded; when/if "-Wall" is an option in the official Arduino IDE, this is going to be the first thing I enable!
34  Using Arduino / Programming Questions / Silly "= vs. == in a conditional statement" question on: August 14, 2011, 12:49:55 am
Hi,
It's been probably drummed into everyone since "Hello World" - use a single = sign for assignment and double (==) to test for equality. Is there any case where using a single-equals conditional is valid or makes sense?

A fair amount of Googling failed to turn up the actual *behavior* or legality of such a statement, only echoes of "be sure to use = for assignment and == for equality". Should
Code:
if(a=b)
return (e.g. "assignment was successful") TRUE always? Or evaluate the assigned *value* (e.g. return TRUE if b was nonzero)? Or undefined / none of the above?

A quick test with Arduino (avr-gcc) suggests the 2nd case. Is this a standard behavior that can be relied upon, or is this left up to the individual compiler author?

(The more real-world case that got me curious: I want to write a routine that processes the contents of one or more fixed-length buffers that may contain a radio packet (filled by an interrupt routine when a packet is received), and envisioned a "getbuf()" function that would return a pointer to the next buffer containing a packet, or NULL if all are empty. The construction
Code:
while(pBuf = getbuf())
{
   ... process the packet in buffer pointed to by 'pBuf'...
}
seems logical enough, IF it is actually legal C of course ;-)
35  Topics / Device Hacking / Re: Read USB data on: August 13, 2011, 12:34:40 am
Are you trying to debug / sniff USB data on a gadget connected to a PC?

I've used a program called SnoopyPro for this (under Windows at least) - looks like here may be its current official home. Can't really be of much without knowing more about what you want to do.
36  Using Arduino / Motors, Mechanics, and Power / Re: Source for timing belts on: August 12, 2011, 11:48:59 am
For a prototype pick-n-place system I'm playing with I got timing belts (tooth / cog belts) and matching pulleys from here:

http://www.smallparts.com/

You can probably find them a bit cheaper other places, but they have an actually usable site search (good for resolving a large dependency chain of parts that must mate), and a large selection of matching belts and pulleys. I used the "40DP" (0.0816 pitch) variety as it seems to be pretty popular.
37  Using Arduino / Motors, Mechanics, and Power / Re: Small motor sourcing? on: August 12, 2011, 11:36:53 am
Why "not just a vibration motor"? I've found these are the tiniest motors you can get, and surplus dealers often have a variety of them in stock:

http://goldmine-elec.com
http://allelectronics.com

Electronic Goldmine shows one with dimensions of .375"L x .2" square (although I think the plastic "square" around the motor is removable to make it even smaller!)

Pager/vibrating motors are ordinary DC motors with a small off-center weight crimped onto the shaft, but these can usually be removed pretty easily. For steppers, the smallest NEMA frame type I found (buyable by hobbyists) was from Pololu, but it doesn't come close to being as small as the pager motors.
38  Using Arduino / General Electronics / Re: Building or use an interrupt controller. on: August 06, 2011, 12:35:51 am
I recently found a couple libraries in the Playground for this, looks like someone has already done the dirty work and make pin-change interrupts pretty useful (e.g. allow you to assign per-pin interrupts and conditions, even though technically each 8-pin port shares a physical interrupt vector). Have a look at PcInt or PinChangeInt, depending on whether you value readability or speed more.

(I don't know enough about ATMega yet to say how simultaneous interrupts will be handled, and whether having them occur on different ports will make a difference.)
39  Development / Other Hardware Development / Re: Mosquino rev2, micropower / energy harvesting Arduino variant - feedback wanted! on: July 26, 2011, 11:16:48 pm
Hi all,
There is now an official first release of the Mosquino mainboard, software and several support boards (available at the Google Code project's downloads section). The hardware under downloads is tested and to the best of my knowledge fully functional, although not all of the software core features (e.g. PWM) have been formally tested yet.

Sleep current consumption is about 2uA from a regulated (3.3V) supply, and approx. 6uA from an unregulated one. There are ways to reduce these further, but that should be good enough for most normal users ;-) Peak undervoltage current is about 80uA for unregulated supply and 0.3mA for regulated. These will be reduced in future versions, but again, I don't see them being a big problem for most users.

All my electronics / Arduino stuff is packed in boxes for the next couple weeks due to home remodeling, but after that, more test results, shields and software to come... soonish :-)
40  Topics / Device Hacking / Re: Sine wave generator from AM radio receiver on: July 18, 2011, 05:13:51 pm
Hi,
It might be overkill and/or not fast enough for your needs, but I posted an approach a little while ago for an arbitrary amplitude + arbitrary waveform generator implemented purely in software: http://arduino.cc/forum/index.php/topic,63604.0.html .

For a one-off project, it's probably easier to follow retrolefty's suggestion of generating a squarewave (tone()) and filtering it. VCO (voltage controlled oscillator) circuits are fun to play with too if you have the time; this may give you a more consistent signal over the entire audio frequency range (won't have to worry about rolloff from the squarewave-filter).
41  Development / Other Hardware Development / Re: Mosquino rev2, micropower / energy harvesting Arduino variant - feedback wanted! on: July 08, 2011, 01:12:12 am
It's aliiiive!

My freetime has been thoroughly zapped lately, but I finally managed to get the first one built and bootloaded. So far only 'hello world' and a sleep test have been run on it, but everything seems to be working so far :-)  Tomorrow (err...today) I should be able to take it into lab (where the GOOD multimeters are) to verify PGOOD/PFULL/UVLO functions and sleep current consumption.

See attachments for pics of the finished board / bootstrapping from a Duemilanove (you probably need to be logged in to see attachments).
42  Development / Other Hardware Development / Re: Mosquino rev2, micropower / energy harvesting Arduino variant - feedback wanted! on: July 08, 2011, 12:46:12 am
@skywalk

Plugging in USB to this board will always supply 5V (regulated to 3.3V) and bypass all other power supplies/shields, so I don't see it as much of a problem for the standard configuration. I can see your point if you want to replace the onboard 3.3V LDO with another voltage. But then my concern is that the FT232 will be sinking current from VCC continuously when the CPU is powered.

For this version an arbitrary regulated voltage (1.8 ~ 5V) can still be supplied through the power shield interface safely - in this case the board will switch over to 3.3 when the USB connection is active. (And VCC can be safely driven with 5V externally for e.g. bootloader programming with the power shield removed.)
43  Using Arduino / General Electronics / Re: Electronics/Arduino in Carry-on Luggage on: June 13, 2011, 05:30:03 pm
I'd second all of the above advice. That said, I've never encountered a problem flying in the US with an Arduino or other prototype PCBs in my carry-on - never even been asked about them. The couple times I've been pulled out of line due to something in my bag, one was a bulky old Hi-8 video deck, and one was a (new in package) shower curtain! I also *almost* got grilled about an LED flashlight (it was obvious it was the examiner's first day or so on the job; another TSA screener came over and calmed her down). But, I've travelled with no end of bulky vintage computer equipment, and even the compressor out of a refrigerator stuffed into my carryon without a second glance - there's no rhyme or reason to what the TSA screener will find 'suspicious'.

A coworker and I did get a plane delayed once due to an electronics prototype in our checked luggage - by this time we were inside the plane and not around for questioning, but the pilot announced a series of delays before takeoff, first that they were "changing a tire" (this magically occurred without the plane lifting or otherwise moving), followed by "some paperwork" related to the tire changing. Afterward we found a TSA screener flyer in the bag and that the prototype had obviously been opened (e.g. bolts missing). To be fair though, this prototype consisted of a large (8x6x4 inches), heavy aluminum box with a PCB and a black cube full of accelerometers, sprawling with wires and liberal blobs of epoxy everywhere inside tacking them down :-) We had also made things easy by taping the appropriate Allen wrench right to the enclosure (mostly for ourselves though).
44  Using Arduino / Networking, Protocols, and Devices / Re: Very low-power radio modules? on: June 10, 2011, 11:03:02 pm
@Magicmike: alas, that project also relies on the receiving radio being active all the time. What I'm looking for is to allow a micropower device to talk to another micropower device (or many) by leaving both the transmitter's and receiver's radios off for 99.99% of the time.

@Marco: JenNet sounds interesting. I didn't see any download links though. Is it released already or is this a future product? (or vaporware smiley-wink ) How do you know it will be open-sourced?
45  Using Arduino / Programming Questions / Re: Algorithm for fast waveform generation w/ amplitude control on: June 10, 2011, 10:33:28 pm
True. But this would make for a pretty big wavetable; I needed to keep it small in order to fit all of the waveforms and the rest of the code (generating waveforms was just a small part of the project).

For anyone wondering, the "phase accumulator" approach as I understand it is to use a much larger table (more points), keep the speed of the timer constant and set the output frequency by skipping a certain # of points each time (the # of points skipped determines the frequency).
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