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136  Using Arduino / General Electronics / Re: LM317T Driving me nuts on: July 04, 2011, 04:56:42 pm
Remember you can put resistors in series or parallel to get closer to the value you want.

And if you use two big resistors in parallel you will cut down the current flowing through each one; hence you may get away with much lower wattage on each resistor.
137  Using Arduino / General Electronics / Re: LM317T Driving me nuts on: July 04, 2011, 05:14:19 am
just a quick question, i dont recognize that component on R1, the arrow pointing at a resistor? How's that suppose to be implemented?

Well, that's a variable resistor, the arrow pointing on R1 represents the third connection of a variable resistor (they have three pins; ref. http://www.pictutorials.com/resistors.htm), the one that moves along the resistant material and makes it change its value.

This circuit is an example of a "variable" current regulator; R1 is the variable resistor (could be a slider, a trimmer or whatever); by changing its value you change the result of the formula Iout=Vref/R1 and you get various currents.

In your case, you need a specific current value, so you don't need a variable resistor; you have to calculate R1 in order to get the needed Iout and use that R1 in your circuit.
138  Using Arduino / General Electronics / Re: LM317T Driving me nuts on: July 04, 2011, 12:13:48 am
I was checking the lm338 and there were some examples.

Precision Current Limiter seems to be a good choice for the LM338 implementation.
Probably will limit the current to 1.4Amps and work from there.

This is the one you need! SImple and effective to your case.
If you limit the current to 1.4Amp you're good to go with your led (ref. datasheet). You can even connect both leds in series (always at 1.4Amp) if you provide enough voltage to the LM338. And then increase the current even more since the LM338 is capable of providing a maximum 5Amps total (with proper heatsink).
139  Using Arduino / General Electronics / Re: Which capacitor with LM317 driving a series of leds? on: July 02, 2011, 11:05:18 am
No matter how many external components you connect to the LM317 and no matter what their configuration is, the LM317 is still a voltage regulator.

:-) Of course it is.
Current regulation is still a side effect of a peculiar configuration where the voltage regulation forces a fixed current on the output.
140  Using Arduino / General Electronics / Re: Which capacitor with LM317 driving a series of leds? on: July 02, 2011, 08:53:47 am
At least read through Grumpy_Mikes epic tutorial: http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

Nice tutorial ... good job Grumpy_Mikes, thanks KE7GKP for the hint :-)
141  Using Arduino / General Electronics / Re: Which capacitor with LM317 driving a series of leds? on: July 02, 2011, 08:37:11 am
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Normally, no capacitors are needed unless the device is situated more than 6 inches from the input filter capacitors in which case an input bypass is needed. An optional output capacitor can be added to improve transient response
I think, this is true only for Voltage regulator. In case Current regulator you don't need any external capacitors, especially if you drive leds with PWM or turn  on-off them rapidly.
What is your set-up?

Plain and simple LM317L (TO-92 package) in current control configuration (with a 60R resistor) feeding a series of six bright white 5mm leds (at 20mA). There's no IC to worry about at all.

As you see, not much to worry about ... but I know if tension goes weird, that can cause damage to those leds (the LM317 does a good job in protecting itself most of the times) and I want to make it failproof (as long it's not overcomplicated). Fact is I don't know if I really have to worry about those capacitors; my first guess: a simple input bypass capacitor (0.1uF disc as per datasheet) can be enough to cover noise coming from the power supply and making the lm317 work without issues (but again, is that even relevant in such a simple circuit?).
142  Using Arduino / General Electronics / Re: Which capacitor with LM317 driving a series of leds? on: July 02, 2011, 07:10:23 am
Ok, this is pretty much what I've already read on the datasheet, fact is I don't want to overengineer it and still I don't want to be too lazy ad miss an important detail.

From the datasheet (and so does CrossRoads suggest too) I read I can put an input capacitor to be used as a bypass and an output capacitor to improve transient response.

Since I still have only a vague idea of what a "bypass capacitor" does and what a "transient response" is, I will start by following CrossRoads' suggestion but will dig deeper into this bypass_capacitor/transient_response stuff ... I really don't like doing things only because I'm told too.

Anyway, my circuit is pretty simple, no need to worry about that too much. It's just my need to understand how it all works. Making up this simple circuits is already a way to deal with more controllable scenarios and give me the opportunity to face basic concepts one at a time.

Btw, I'm using this: http://cgi.ebay.it/24V-DC-2-1A-50W-Regulated-Switching-Power-Supply-/250672045980?pt=LH_DefaultDomain_0&hash=item3a5d37df9c to power the circuit. I wonder if knowing that can help choosing the right capacitor.

143  Using Arduino / General Electronics / Re: LM317T Driving me nuts on: July 01, 2011, 02:37:37 pm
It should be like this:  Voltage Reg. vOut ---> RESISTOR ---> LED1 ----> LED2 ----> GND

Just consider Led1 + Led2 as a single Led that needs tyq
144  Using Arduino / General Electronics / Which capacitor with LM317 driving a series of leds? on: July 01, 2011, 09:22:50 am
I'm driving 6 white led in series with a LM317 used as a current regulator out of a 24V DC power supply. I wonder if I should/could use a capacitor (on the input/output side of the LM317).

I'm open to suggestions since I'm relatively new to this stuff :-)
145  Using Arduino / General Electronics / Re: LM317T Driving me nuts on: July 01, 2011, 01:02:11 am
Quote from: SgtOneill
Oh boy... i must be torturing these LED  smiley-red

Just use the LM338 and build a Current Limiting Circuit with that. Driving LEDs with voltage can be frustrating (you are experiencing that right now). The key for success is driving them with current. Take a look at LM338's datasheet, you'll find the answer.
146  Using Arduino / General Electronics / Re: [Mega 2560] external 5V power supply on: June 28, 2011, 03:44:30 pm
So applying a +5vdc to the shield +5vdc pin will power everything required on the arduino board.

That's good to know. Thanks for the hint :-)
147  Using Arduino / General Electronics / Re: [Mega 2560] external 5V power supply on: June 28, 2011, 03:08:06 pm
The "5V" pin is just that - 5V. It can be input or output.

As far as I know 5V is not enough to run the Mega256 properly (recommended input voltage is 7-12V).

If I understand it right, BlazeX thinks he can power the Arduino with this 5V too, I think that's not good.
148  Using Arduino / Microcontrollers / Re: Arduino Mega2560 as ISP for ATMega328 and ATTiny2313? on: June 27, 2011, 12:06:56 pm
if it can be helpful, sometime i have the same error trying thru my 2009 to burn atmega328 st.alone.
i just need to manual press reset button on the 2009 and click the upload button on the screen. it works.

At the moment I stopped trying. Being working on some other stuff. I will try again though, and explorer this reset related procedure. Thx for the hint.
149  Using Arduino / Storage / Re: Which is the first address index of an EEPROM? on: June 27, 2011, 11:17:57 am
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Have you looked at the header file and source code for the Wire library?

Actually ... no. But I will. That could only be helpfull.

It's nice to know there's people like you, that knows the source so much better than me :-)
Really, no sarcarsm here, I appreciate your comments a lot.
150  Using Arduino / Storage / Re: Which is the first address index of an EEPROM? on: June 27, 2011, 08:16:35 am
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I suppose the first eeprom register index should be 0 (like in arrays indexing), but I'd really like to be shure about that.
Did you ever stop to think about why the first array index is 0? The index is an offset from the memory location where the first byte is stored. Logically, then, it follows that the first EEPROM address is 0.

Ok. In fact, meanwhile, I did a few more attempts. Now things are clear.
No negative register indexes have any sense at all for eeproms. And yes, first eeprom register index is zero.
Using negative indexes, I was looking at garbage values taken from who knows where.

But I still get a read wrapping when I go past the last eeproms register index. I'm using a few 24C02 (2kbit = 2k x 8byte = 256byte). Everytime I try and read values behind the last byte I get the first eeproms memory value back. That's using subsequent Wire.requestFrom() calls; I set the initial reading index with Wire.send(0) and keep reading past the 32nd memory page.
That's interesting and maybe usefull. Anyway I have to take into account it can be done.

I'm still wondering how does Wire.available() cope when negative indexes are used, there's something I still have to investigate regarding this peculiar condition.

Thanks for the hint and the observation :-)
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