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6376  Using Arduino / Microcontrollers / Re: One arduino - 2 baud rate? on: July 12, 2011, 10:48:32 am
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As for the not recommended part, does it cause any damage to the arduino and/or sensors/gps?
No, the problem is "How do you detect the bit rate if it's changing from one transmission to another?"

The only real way is to do some low-level timing of the bits over several bytes or a known sync byte at the start of every transmission. Not rocket science but I think you'd want a good reason to do it.

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Rob
6377  Using Arduino / General Electronics / Re: 74HC595 output voltage on: July 11, 2011, 08:25:12 pm
595s are not designed for high-current loads.

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The relay is drawing 5.3 milli-amps and not turning on.
What does the relay spec say it needs [EDIT: 5v @ 170R = ~30mA, I could have worked that out myself smiley). 5.3mA would not be enough I would think. The smallest I've seen need about 20mA.

You can add a darlington array chip (ULN2803 or similar) or use a shift reg that's designed to drive loads (TLC5927 or similar).

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Rob
6378  Using Arduino / Motors, Mechanics, and Power / Re: Best way to insure fool-proof control of a powerful servo? on: July 11, 2011, 08:18:03 pm
This is not a high-current load though, despite it being a "powerful" servo it still has a logic-level input. Somewhere inside you would probably find some amplification but you shouldn't have to worry about it.

Your circuit description sounds right.

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Rob
6379  Using Arduino / Motors, Mechanics, and Power / Re: Best way to insure fool-proof control of a powerful servo? on: July 11, 2011, 07:40:29 pm
That circuit won't work as the "pulse" signal will be floating whether the transistor is on or off.

How do you define "foolproof"? Do you just want to protect the Arduino pin?

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Rob


6380  Topics / Product Design / Re: NutriSmart Embedded Design on: July 11, 2011, 08:20:25 am
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technology in it self isn't bad, it's what bad people use it for that's bad...
The argument used by every techo working on projects from the cross bow to the nuke.

But that aside, I think it could be good for those with allergies, knowing there's say peanuts inside might be a good thing for many people.

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Rob
6381  Using Arduino / Project Guidance / Re: Thermocouple data graphing in Libreoffice Calc - real time clock shield required on: July 11, 2011, 08:07:21 am
As long as the timing isn't really critical I'd just let Excel read the PC time and use that. I think this will introduce small timing errors as serial data is buffered here and there, but maybe not and maybe that won't matter to your application.

Another way to get pretty accurate timing is to have the Arduino attach the value from millis() to each sample then have Excel simply add that offset value to the time the job was started. This will be very accurate.

Similarly just ensure that the Arduino samples every N mS in which case the offset from the start is implied.

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Rob
6382  Using Arduino / Programming Questions / Re: Digital pins D8-D15 briefly high at upload on: July 10, 2011, 07:15:11 pm
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I was under the impression that this was the case during ICSP programming.
Correct, I'll go back to Arduino 101 class smiley

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Rob
6383  Using Arduino / Project Guidance / Re: wake up arduino through serial comm & interrupts on: July 10, 2011, 07:13:20 pm
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The other signal is the output from a photo interrupter
Which is probably open collector, but I still don't see how it can pull against the 14001 output  smiley-confuse

BTW you can get logic gates in a single-gate pack (SOT23-5) these days, great for this sort of thing where you only need 1 or 2.

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the current pin change interrupt library seems to be adding 360bytes to the footprint.
All you need is an ISR I would think, that will use almost no flash. Get rid of the attachInterrupt() stuff and handle the logic in the ISR.

ISR xx() {
   if (sleeping)
      do this
   else
      do that
}

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Rob
6384  Using Arduino / Motors, Mechanics, and Power / Re: Other ways of controlling water flow on: July 10, 2011, 07:15:45 am
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does anyone know where to find Plaster of Paris in Australia
Maybe art supply shops.

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Rob
6385  Using Arduino / Programming Questions / Re: Digital pins D8-D15 briefly high at upload on: July 10, 2011, 07:13:58 am
During upload the processor is in a reset state and all IO pins should be Hi-Z and floating.

Do you have anything else connected to these pins?

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Rob
6386  Using Arduino / Motors, Mechanics, and Power / Re: Other ways of controlling water flow on: July 10, 2011, 03:04:47 am
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should I risk it?
I would say no. It's hard to see with that photo but I would expect only a single outlet and there would be no practical way to separate the valves.

Another thing to think about is the control voltage, anything made for a fridge will use mains I reckon which is more difficult to work with, and if you get it from the US that will be 110v.

Personally I would not buy anything from somewhere that didn't provide a full data sheet and in this case mechanical drawings. Maybe you can get these from GE.

Have a look at this

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&productId=169835&catalogId=10001&freeText=169835&app.products.maxperpage=15&storeId=10001&search_type=jamecoall&ddkey=http:StoreCatalogDrillDownView

Small ports but they might have larger versions.

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Rob




6387  Using Arduino / Motors, Mechanics, and Power / Re: Other ways of controlling water flow on: July 10, 2011, 02:23:38 am
That Amazon valve looks to me like it's a mixer, ie hot and cold into a single output. If that's the case is that what you need? It's not normally the sort of thing used for garden control.

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Rob
6388  Using Arduino / Motors, Mechanics, and Power / Re: Other ways of controlling water flow on: July 10, 2011, 01:50:48 am
I haven't looked for ages but solenoid valves from places like Bunnings aren't that expensive are they?

BTW, it's VegEmite, (I had to go look at a jar to make sure smiley)
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Rob
 
6389  Using Arduino / Project Guidance / Re: wake up arduino through serial comm & interrupts on: July 09, 2011, 07:23:51 pm
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In this way, we can use INT0 for another purpose when arduino is awake.

The 14001 is not open drain though so how does the "other purpose" work when connected to a hard voltage?

Another option is a 74xx126 tristate buffer or a 4066 analogue switch.

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Rob
6390  Using Arduino / Programming Questions / Re: Fixing the randomSeed() function (when using analogRead) on: July 09, 2011, 11:11:51 am
There's no way you'll get very random from reading an ADC as you've found out, but there is low-value noise there. If you look at the LSB for each of those values you get this

0001 1110 0001 0101 1110 0001 0110 1000 0110 1001 0110 1001 1011 0100 1001 0110

Put that together and you have something resembling two 32-bit random numbers (maybe). How about doing that 100 times and seeing just how random it is.

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Rob
 
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