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6376  Using Arduino / Networking, Protocols, and Devices / Re: Fast communication to PC with low Arduino footprint on: May 17, 2011, 11:30:11 am
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Sampling + sending raw data through Serial.print (baudrate 115200): 2.2 Hz
That may have been the serial blocking, a non-blocking version might do a lot better although it will never match SPI.

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Rob
6377  Using Arduino / Project Guidance / Re: Coin Counter on: May 17, 2011, 11:26:28 am
This can be done, it just needs some deep thought.

I'm not sure a method of counting the 30 coins was proposed yet. I was going to suggest PCINTS but there are only 24 of them.

I do have an idea but it's late here, if nobody has come up with something by tomorrow morning I'll post it.


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Rob
6378  Development / Other Hardware Development / Re: ATMEL Mega1284P evaluation board avalible on: May 17, 2011, 11:05:20 am
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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.

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"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.

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"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).

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"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).

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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.

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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.

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Rob


6379  Using Arduino / Project Guidance / Re: Coin Counter on: May 17, 2011, 10:11:49 am
If you use LED driver chips like the AS1108 (this does 4 7seg displays) you can run as many displays as you like with 3 pins.

MAXIM also make chips (like the MAX7219) that will run these displays, some go up to 8 displays per chip.

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Rob
 
6380  Using Arduino / General Electronics / Re: Using one circuit to switch another - (basic!) on: May 17, 2011, 10:01:01 am
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The voltage is 5.9v
Then another (simpler) option is to step it down with a voltage divider.

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Rob
6381  Using Arduino / Project Guidance / Re: Coin Counter on: May 17, 2011, 09:51:27 am
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it doesn't even need to be an true LCD it can just be a digit counter, that is just used for numbers.
You can get 7-segment LCDs like in a multi meter, I haven't seen them around for years but there must be driver chips for them (we used to use XOR gates).

Or you could use 7-segment LEDs, no speed issues with them.

Or "serial" displays where you just spit out serial data with the numbers.

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Rob
6382  Using Arduino / Networking, Protocols, and Devices / Re: Fast communication to PC with low Arduino footprint on: May 17, 2011, 09:39:51 am
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Is there some hardware that I could simply connect to the Arduino and then use the SPI library to talk to the computer?
Yep, another Arduino.

The first one does nothing but read sensors and spit data out the SPI.

The second one does nothing but read the SPI and spit data out the USB (assuming it can do > 115200 over USB, I've not tried higher than that speed).

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Rob
6383  Using Arduino / General Electronics / Re: Using open drain to turn a DC/DC off on: May 17, 2011, 09:30:47 am
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then the pull up would be pulling the pin high to VDD if everything's ok, and connecting it to RTN (ground) if not.
That's right.

If the output is open drain then it will swing from 0v when the transistor is switched on to whatever voltage you pull it up to when it's not. The drawing shows it connected to VDD but if you connect the PU resistor to say 5v then that will be the high level presented to the DC/DC converter as long as they have a common GND.

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Rob
6384  Using Arduino / General Electronics / Re: Using one circuit to switch another - (basic!) on: May 17, 2011, 09:14:56 am
You have to share GNDs between the two systems. If the current circuit has a voltage approx 4.5-5v (say 3 AA cells) you could feed the signal that powers the LED directly into an Arduino pin.

If it's a higher voltage (or a lot lower) a transistor would work, using a diagram from that link



you would run a wire from where it says "non-inductive load" to the Arduino input, and "Microcontroller IO port" is your LED circuit. The signal will be inverted so if you read a LOW the button is pressed.

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And do both circuits need to be powered from the same power source for this to work?
No, just share GND.
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Rob
6385  Using Arduino / General Electronics / Re: Need a connector on: May 17, 2011, 09:04:12 am
I don't quite get what you mean. I've never seen a connector that will allow you to remove a LED from an enclosure, they are normally fixed in place. Something like this

http://www.pololu.com/catalog/product/1901

will allow you to remove say the enclosure lid and disconnect the LEDs from the PCB.

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Rob
  
6386  Community / Bar Sport / Re: Employment for Arduinoites on: May 17, 2011, 07:11:25 am
Maybe, but you can still develop an "Arduino compatible" device with no legal issues, and in that case you would have to use the word in the ad to attract the right people.

OTOH if you are an Embedded EE you'll pick up Arduino in about 20 minutes (if you already know AVRs) so maybe "Arduino" is not the thing to ask for even if that's the intended platform for the applicant.

FWIW I always search for the word "embedded", that seems to return the best results. But there are precious few interesting jobs around from what I can see and the few I have found have been in "a great central CBD location", why the hell would I want to battle the subway or traffic for 2 hours a day? Why aren't there any good jobs in a "nice leafy outer suburb" or a "quite small town".

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Rob
  

6387  Development / Other Hardware Development / Re: ATMEL Mega1284P evaluation board avalible on: May 17, 2011, 06:16:52 am
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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.

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Would love to see the outcome of this thread.
Wouldn't we all. The pressure's on Crossroads smiley

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Rob

6388  Community / Bar Sport / Re: My electric blanket doesn't work ... on: May 17, 2011, 05:41:29 am
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Anything above 17C outside and I'm considering removing clothing
As I said, anything below 30C and I'm considering adding clothing smiley

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Guess it's largely relative though.
Ain't that the truth.

As I understand it humans as a species prefer 25C, it's just that we all live in different places and get used to a certain range. I used to live in a cold place and was well happy with low temps, now I live in hot places (mostly) and prefer the heat.

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Rob

6389  Using Arduino / Programming Questions / Re: array[].length -Workarounds ? on: May 17, 2011, 02:36:17 am
With these multi-dimensional arrays an array of structures is often a better approach, with a global telling how many items in the array.

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but without being able to determin the last item of an array I loose its main advantage as a list.
With structures you can have a "last item" flag but this is a bit wasteful when a single external variable will do the same.

Is there any reason not to have a item counter as a global var?

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Rob
6390  Using Arduino / Project Guidance / Re: Colon on 4 digit 7 segment display on: May 17, 2011, 02:28:01 am
These displays are a PITA, the degrees led and the colon all wired in parallel so you have to physically blank out L3 with a marker or some tape or something.

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Rob
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