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1  Using Arduino / General Electronics / Re: how can i read negative voltage in analog pin of arduino board? on: June 23, 2012, 04:01:48 pm
Using 10k resistors for the divider will be a good compromise between accuracy and reducing the risk of damage if the input goes a bit too low - high resistance protects against damage, too high and the accuracy will suffer.  Placing a diode between analog pin and ground (anode to ground) can afford protection (ideally schottky diode)

If the voltage you are measuring has a very high source impedance you will need another method - what generates the signal ?

well i sampling voltages in RLC circuit and i have to relate with transfer function of circuit.
2  Using Arduino / General Electronics / Re: how can i read negative voltage in analog pin of arduino board? on: June 23, 2012, 02:40:39 am
Note you need to connect the ground of your external voltage to the arduino's ground. Plus if the voltage is any greater than -5 you are screwed, or rather your arduino is.
thanks for your answer, a little question, analog pin will be damaged if I connect negative voltage? if yes, why?
3  Using Arduino / General Electronics / Re: how can i read negative voltage in analog pin of arduino board? on: June 22, 2012, 11:15:13 pm
Put a resistor divider 1:1 between source input and +5V . Middle point to analog in. You will read 0 at -5V and 2.5 at 0. Do a reverse in software
thanks for your answer.i cant believe this easily solution to my problem. smiley-eek-blue
4  Using Arduino / General Electronics / Re: how can i read negative voltage in analog pin? on: June 22, 2012, 09:59:08 pm
How negative and how much does it vary? Good answers come from good information, you have supplied none except a vague reference in the title...

Doc
about -5 V.thanks for your answer
5  Using Arduino / General Electronics / how can i read negative voltage in analog pin of arduino board? on: June 22, 2012, 09:14:02 pm
Hi guys, i have a little question about the analog pins of arduino board, can someone help me please with this issue? Thanks
6  Using Arduino / Networking, Protocols, and Devices / Re: i2c and A/D on: April 08, 2012, 10:34:14 pm
The compiler gets confused by the number 0, which might be a pointer or it might be a number. Putting (byte) there is a typecast which tells it which "version" of zero to use.
i see
thanks a lot.
greetings.
7  Using Arduino / Networking, Protocols, and Devices / Re: i2c and A/D on: April 08, 2012, 10:18:51 pm
hey someone can helpme please?

i dont understand in this line
Wire.write((byte)0);

especify why add "((byte) 0)" 
what does when i add "(byte)"?
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