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10756  Using Arduino / Microcontrollers / Re: High Tempratur Atmega88/168 on: April 22, 2011, 09:21:28 am
Dear all,
i need the 150 degree in research application.
I will take care about solder and other components for 150 degree Celisius.
Please, and please: My Question:
Can i use Arduino for the Atemage168 Automotive?
Thanke you
Turi79

Well my opinion is no, not if you are actually going to subject the board to 150C operation. Subjecting most electronic components to 150C/330 F far exceeds their maximum ratings so you would have to research every single component on a arduino board (including the board material and the IC socket and other connectors) to see if they can operate at that temp and if not try and find suitably rated components.

You are dealing with a very limited application requirement. I recall special Motorola ICs that were designed to be used in deep water oil well drilling applications that were rated at around 350F max temp range but the costs were extreamly high and I'm sure the other support components needed were very difficult to source.

Lefty
10757  Using Arduino / General Electronics / Re: Power for a few more seconds after disconnect on: April 22, 2011, 09:05:08 am
Just for interest, 5 hours after I started the sketch is still running. The power is down to 3.9V.

So as a proof of concept, it appears that a couple of ultracapacitors can keep your sketch running for 5 hours. This particular sketch spends all its time lighting up LEDs, which is probably a bit of a torture test, comparing to monitoring temperatures etc.

The two capacitors I used cost me $US 32 (for both).

Whilst they take a while to charge, I think this is acceptable. After all, you put charged batteries in as a battery backup don't you, not discharged ones. Either you could organize a more sophisticated charging circuit, or just pre-charge them.

Something like this could keep a security system running for hours, even during a power outage. And if you double the number of capacitors, you double the time they will keep running. Coupled with the suggested power board, with its DC to DC converter, you could probably squeeze something like 8 or more hours of performance out of them (or 16 if you use 4 capacitors).


The question I would have is how does this compare to a more traditional back-up using batteries as far as initial costs, volume (size) used, and recharge time, etc. Most batteries have a pretty flat voltage discharge curve while the super cap would need some kind of boost voltage regulator to match battery voltage Vs time performance, which might be critical to some applications such as using analog input values where a changing reference voltage would hurt calibration accuracy.

 So while super caps are interesting I haven't yet seem an application where a properly sized battery doesn't perform as well or better for less costs and space requirements. Super caps have been around for quite a while now, but I've seen few pratical applications for them, and I don't count the auto stereo installations where I think the visual appeal is more important then what they actual add to the systems performance. But then maybe I'm being too pessimistic? Show me the math.  smiley-wink

Lefty
10758  Using Arduino / Motors, Mechanics, and Power / Re: OPI 110 optoisolator on: April 22, 2011, 08:46:03 am
Quote
Firstly that's a triac, not a thyristor,


The term "thyristor" covers a family of four layer semiconductor devices including triacs and SCRs:

http://en.wikipedia.org/wiki/Thyristor

Lefty
10759  Using Arduino / Installation & Troubleshooting / Re: Whats this mean?!?!? on: April 21, 2011, 06:03:11 pm
With virtually no other context, I think it means that 42 does not equal 83.

Well assume in the context of a failed upload. At least that is how I took the question.

Lefty
10760  Community / Bar Sport / Re: 48รท2(9+3) = ? on: April 21, 2011, 06:01:04 pm
Quote
And that is the fundamental issue. Not everybody agrees with that.

Heck, we can't all even agree on which side of a road to drive on.  smiley-wink

10761  Using Arduino / General Electronics / Re: Power for a few more seconds after disconnect on: April 21, 2011, 03:04:31 pm
OK you have a possible 'hold power for a little while' method/circuit. But I still haven't seen how you are going to detect that normal power is starting to go bye bye, so as to take advantage of the power holding circuit?

Lefty
10762  Using Arduino / Installation & Troubleshooting / Re: Small negative voltage on analog input on: April 21, 2011, 03:00:34 pm
Hello.
I have just one easy question - will a small negative voltage on the analog input damage the Arduino board (Mega 2560)?
My project involves reading some volages from a measuring circuit, and sometimes (when the measured device operates at a higher frequency than the op-amp in the circuit can handle accurately), about -10mV to -15mV appears on the analog input. Is this a problem for the board?


Shouldn't be a problem. The negative spec is -.5 below ground I believe. That's when the internal negative clamping diode will start to conduct and it can only handle a small amount of current. So -10 - -15 mv should not be a problem in my opinion.

Lefty
10763  Using Arduino / Motors, Mechanics, and Power / Re: Why do I need a diode over the coil contacts on a relay ? on: April 21, 2011, 02:50:11 pm
An interesting aspect of this is that one can often hear a difference in the relay's action when switched off between if there is a diode installed or not. When there is no diode the relay's off action is faster and on larger relays one can hear the sharp click sound, but with a diode installed the off action sound is more muted and the speed is a little slower.

 I noticed this when checking out a larger industrial 4 pole double throw 24vdc relay at work, using a scope to try and quantify the size and duration of the generated transient pulse. It was quite a short pulse, maybe just a microsecond or so, but easily 100+ volt peak could be seen on the scope.

Lefty
10764  Using Arduino / Programming Questions / Re: Encoder Output on: April 21, 2011, 11:12:22 am
Quote
I have the encoders going straight from pin 6 and 7 to the encoder. And the middle pin of the encoder going to ground.

That will work but only if you either wire external pull-up resistors from pins 6 & 7 to +5vdc, or enable the internal pull-ups for both those pins.

Lefty
10765  Using Arduino / Motors, Mechanics, and Power / Re: Why do I need a diode over the coil contacts on a relay ? on: April 21, 2011, 10:58:39 am
I'm sure the reply to this is common knowledge for those with experience, but I can't understand the purpose of a diode over the coil of a relay.

Don't get me wrong - I have been told I need it, and I don't dispute that, but I would like to understand why.

Any explanation or links in newbie terms (that means small words)?


When you apply a voltage to a coil is creates a magnetic field. When you remove the voltage the magnetic field collapses and creates a reverse polarity voltage and can be many times the value of the original applied voltage (X4 in my o-scope experiments). This creates a transient voltage pulse that can damage other components in the circuit that are not rated for this polarity or the higher voltage created, things like semiconductors and caps have a maximum voltage limit and breakdown if exceeded. Having a reversed biased diode across the coil allows the diode to conduct for reverse polarity voltages and creates a 'short circuit' across the coil that allows the pulse to be dissipated in the resistance of the coil wiring.

Lefty
10766  Community / Bar Sport / Re: Presented without comment on: April 20, 2011, 10:02:14 pm
Great, opens up the Arduino platform to a whole new user class age group of people.


Lefty

10767  Using Arduino / General Electronics / Re: Arduino Uno not providing power? on: April 20, 2011, 05:12:56 pm
Quote
the led only need 20ma to power up; a exemple: if you plug a 500ma usb on a arduino that need 40ma alone, the arduino will take only 40ma from usb. this is basic eletrical enegering. 


I'm afraid your basic electrical engineering needs a refresher course. 20ma is a pretty normal recommended continous current for a LED. However the LED does not determine this value, the current must be controlled external to the LED, normally with a series current limiting resistor. Once a LED has greater then it's forward voltage drop applied it will draw excessive current unless controlled externally.

I really don't care if you get this or not, what I'm trying to prevent is other newcomers reading your post and thinking they don't require the use of series resistors with LED because that will lead to damaged arduino boards and burned out LEDs.

Lefty
10768  Using Arduino / General Electronics / Re: Arduino Uno not providing power? on: April 20, 2011, 03:56:58 pm
20ma that should not damage the chip.

How is the led current being limited to 20ma?

Lefty
10769  Using Arduino / Installation & Troubleshooting / Re: Voltage regulator getting hot on: April 20, 2011, 03:55:39 pm
 I already answered that.
10770  Using Arduino / General Electronics / Re: Arduino Uno not providing power? on: April 20, 2011, 03:52:50 pm
Quote
this not short or damage atmega328.

Yes it will. To prove it to yourself measure the current you are allowing to flow through that led. Then note that the absolute maximum safe output pin current is 40ma.

Lefty

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