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6406  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
6407  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
6408  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
  
6409  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
  

6410  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

6411  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

6412  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
6413  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
6414  Development / Other Hardware Development / Re: ATMEL Mega1284P evaluation board avalible on: May 17, 2011, 02:18:50 am
Nice, getting a bit full but has a good range of features.

The 32kHz xtal, is that really an HC49 case, normally they are the watch crystal style.

The battery holder will probably clash with the headers and dip socket.

Are the mounting holes at good spacing, .1" preferably but at least whole mm.

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Rob
 
6415  Development / Other Hardware Development / Re: ATMEL Mega1284P evaluation board avalible on: May 17, 2011, 12:28:17 am
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 smiley

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Rob
6416  Community / Bar Sport / Employment for Arduinoites on: May 16, 2011, 08:27:22 pm
There's been a lot of requests for people to do paid work on Arduinos lately, mostly (but not all) for whimsical projects like Darth Vader helmets etc.

So I thought I'd see if Arduino has reached the more mainstream job market yet and searched for "Arduino" on one of the main IT jobs sites (SEEK).

Results, zip.

So I guess not yet.

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Rob
6417  Using Arduino / Programming Questions / Re: 8mhz Clock Signal on Mega on: May 16, 2011, 08:15:29 pm
You can generate a clock signal using the buffered clock output (CLKO or PE7)...oh wait, another useful pin not brought out on the Mega  smiley-mad

OCR1A = 0; // 8 MHz

This may divide by 65k, as the counter might increment then compare, try 1.

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Rob
6418  Using Arduino / Microcontrollers / Re: [SOLVED] programming ATmega328p - undefined reference to _CLI() error on: May 16, 2011, 08:11:05 pm
OK, I get that, it's context safe and good "future proofing" in case you forget a year later and call that old useful function from an ISR.

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Rob
 
6419  Using Arduino / Programming Questions / Re: "Error Message" Interpretation on: May 16, 2011, 07:58:51 pm
This compiles just fine (sorry about the crap formatting)

Code:
//Example 01 : Blinking LED

# define LED 13  // LED connected to
                //digital pin 13
               
void setup ()

{
 pinMode( LED, OUTPUT ) ;   // Sets the digital pin as output.
    digitalWrite( LED, HIGH);  //Turn the Led on
 
  delay(4000);               // Waits for
 
  digitalWrite(LED, LOW);    // Turns led off
 
  delay (4000) ;             // Waits for 
 
   digitalWrite( LED, HIGH);  //Turn the Led on
   
   delay(500);               // Waits for
 
 digitalWrite(LED, LOW);    // Turns led off
 
  delay(500);               // Waits for
 
}

 void loop()
{

}

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Rob
6420  Topics / Interactive Art / Re: Noise reduction through deletion, not averaging. on: May 16, 2011, 07:46:21 pm
Well presumably at present you do something with the readings. So just don't do that something with a 0 reading.

if (getReading() != 0) {
   doSomething();
}

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Rob
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