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61  Community / Website and Forum / Re: Nick Gammon on: July 14, 2014, 12:03:58 pm
A great loss to the forum and the community. Nick produced a great body of work, I hope he keeps his web site up.
62  Development / Suggestions for the Arduino Project / Re: Does Arduino have a future? on: July 14, 2014, 11:57:13 am
This means you will have very long occasional write latencies with SD cards on the SPI bus.

I think I noticed this while working on a recent project and wondered why it happened.
63  Products / Arduino Yún / Re: Any open source / free alternative to Temboo? on: July 12, 2014, 06:26:45 pm
@Jake, looking good there!. I've found GroveStreams to be very responsive to questions and issues. Bugs get fixed extremely quickly (I have found a few but I'd categorize all of them as minor or very minor) and emails from Mike Mills, the founder, are common. Mike is always looking to improve the service, and is genuinely interested in what users have to say, so don't hesitate to offer suggestions on the forum or via the email address on the support page.

Edit: I see you have °F and °C, that's a great example of the automation that GroveStreams offers. Only one of the two temperatures would need to be uploaded, then a derived stream could be created with the appropriate calculation.
64  Products / Arduino Yún / Re: Any open source / free alternative to Temboo? on: July 11, 2014, 02:53:26 pm
I've been using GroveStreams for many months now, and it's by far the best such service I've seen. Less than 20 datastreams and less than 10K transactions/month are free. Rates for higher levels of service are very reasonable. It has very powerful and flexible data analysis and reduction capabilities, automation/alerts, charting, etc. Here are a few charts from a project I've been working on.
65  Using Arduino / General Electronics / Re: My DS1302 RTC gets ahead of real time on: July 11, 2014, 12:45:35 pm
Could i use regular battery in my breakboard, which is made to use a rechargable coin cell? That is what i am asking, how to go about not using a rechargable coin cell battery.
Multimeter on battery pins on the board gives me 4.75V, so i guess i can't.
Or, could i use a 3.7 v li-ion 1090 mAh battery pack?

Depends on what else is in the circuit. Would really need to have a schematic for the board. DS3231 is fine with a 3V backup battery. See the circuit on the first page of the datasheet. Very simple, the battery just goes from the VBAT pin to ground. Again, not knowing the circuit for this particular board, but it may be possible to just remove whatever circuitry was involved with the rechargeable battery and connect a regular lithium coin cell directly to the DS3231 VBAT pin.

Datasheet says the VBAT voltage can be anywhere from 2.3V to 5.5V, with 3.0V being "typical". So a pair of AA or AAA cells would also work. But that would be gross overkill, as would a Li ion pack with 1090mAh capacity.
66  Using Arduino / General Electronics / Re: My DS1302 RTC gets ahead of real time on: July 11, 2014, 11:01:47 am
Temperature compensation seems to work very well here, although I haven't done any extreme tests. I have a couple gadgets with DS3231s sitting on window sills. They catch direct sun and in the winter probably are cooler than the rest of the house. They've been operating continuously since last fall sometime and are both within 5-10 seconds. Like I said, that's not an extreme test, but I've tried non-temperature compensated RTCs in those same locations and they drift a lot farther than the DS3231s, and also a lot farther than non-temp compensated RTCs in other parts of the house where temperature is more constant.

I use regular lithium coin cells for all my RTCs, including DS3231 and DS3232. I use CR2016 mostly, but also some CR1220 (which may be a bit on the wimpy side, but should still last for years). I hardly see the point in a rechargeable cell, estimates I've seen indicate that the regular lithium coin cells should last 5-7 years.
67  Using Arduino / General Electronics / Re: My DS1302 RTC gets ahead of real time on: July 11, 2014, 08:03:50 am
I got my cheap ds3231, this one is loosing 1-2 seconds a day. I remember you guys telling me this one can be calibrated by code. Where should I research that. Any pointers?

Everything is in the datasheet.

DS3231 has an aging offset register that allows the oscillator to be adjusted in approximate 0.1 ppm steps. It's an 8-bit register, so maximum adjustment is less than 13 ppm.
Stated accuracy for DS3231 is ±2ppm from 0°C to +40°C. This is about 0.17 seconds per day.
One second per day would be 11.6ppm, way out of spec.
The aging offset register can compensate for that, but not much more.
Good luck.
68  Using Arduino / Project Guidance / Re: Can an Arduino be powered by a Rochelle Salt Crystal? on: July 04, 2014, 11:52:06 am
@jremington, very cool stuff, thanks. I should have known!
69  Using Arduino / Microcontrollers / Re: Atmega328P-PU identifies itself as 328-PU on: July 04, 2014, 08:16:28 am
This sounds like another example of why I avoid eBay. I know what you mean though, I also wonder why someone would go through the trouble. Not sure what the going price is in the UK, but if I buy 10 from Mouser, they're under $3 each. Buy 25 and they're just over $2. I've never heard of mis-programming changing the signature bytes, I assume they are truly read-only (datasheet says they're in a separate address space). If somehow they can be written, then why not just change them back to what they're supposed to be. I would not assume that just because they run fine that they are fine. The only way to truly know would be to test them at and beyond the stated limits for temperature, supply voltage and clock frequency. In order to interpret the results of such tests, one would need information that probably only Atmel has. To the contrary, given that these chips have two strikes against them (suspicious origin, unexplained signature byte deviation), I would assume that they are not OK. I would not want one controlling some critical system in my car or in my F-22  smiley-wink
70  Community / Gigs and Collaborations / Re: 50 Hz mains frequency monitor - requesting a penpal on: July 03, 2014, 10:18:31 pm
When the load is high, it drags down the generators, they turn more slowly. It's not as much about pricing as managing demand with fewer peaking resources.

I was not familiar with the dynamic demand concept. Interesting.

Certainly the frequency sensing is trivial. The trick will lie in designing algorithms that are effective enough but that consumers do not perceive as unnecessarily intrusive. I don't want my air conditioner going on strike completely on a 95°F (35°C) day. Scaling back a bit might be OK. More aggressive algorithms might be suitable for certain appliances. But let's face it, the culprit on hot days is A/C, not teapots.
71  Using Arduino / Project Guidance / Re: Can an Arduino be powered by a Rochelle Salt Crystal? on: July 03, 2014, 10:08:14 pm
72  Using Arduino / Project Guidance / Re: Can an Arduino be powered by a Rochelle Salt Crystal? on: July 03, 2014, 08:43:59 pm
How much power, and at what voltage, will your crystal supply?

I'm not optimistic. An Arduino, due to ancillary circuitry on the board, will use a couple hundred milliwatts. A standalone AVR microcontroller could improve that significantly, maybe by as much as a couple orders of magnitude (absolute best case). But the transducer to play music may largely offset those savings. Of course the crystal will require continuous or at least regular mechanical input. I'm not up on specifics, but I'm thinking that the voltage generated by such a crystal will be way too high to operate an AVR microcontroller (typical range 1.8V to 5V). So there will be losses introduced by the conversion needed.
73  Using Arduino / Microcontrollers / Re: Atmega328P-PU identifies itself as 328-PU on: July 03, 2014, 07:57:15 pm
Where did these chips come from?
74  Using Arduino / Programming Questions / Re: Downgrade arduino. on: July 03, 2014, 02:21:59 pm
I mostly use Arduino-Tiny and to a minor extent the HLT core, have had no trouble with either and 1.0.5.
75  Community / Exhibition / Gallery / A serial data logger on: July 02, 2014, 10:55:17 pm
This is a project I've been wanting to do for a while. A lot of my projects write debug and other status information to the serial port. Fairly often it seems that I have to let them run for hours or even days to catch an elusive intermittent bug. Until now, this has meant keeping a PC running with a terminal program connected to the microcontroller to log the serial output, which seems pretty inefficient. My primary goal with this logger was to improve that situation.

Hardware consists of an Uno or compatible, Adafruit's Micro SD breakout board, a button switch and three LEDs. It should be easily adaptable to work with the Micro SD on an Ethernet shield or other hardware. (I use the card detect contact on AFI's board, I don't think the shield has that feature, but it would be minor to remove it from the code.

The serial input is double-buffered and interrupt driven to maximize throughput. Details, code and schematic are at:
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