how can i read negative voltage in analog pin of arduino board?

Other Hardware General Electronics
1

Hi guys, i have a little question about the analog pins of arduino board, can someone help me please with this issue? Thanks

2

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

3

Docedison:
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

4

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

5

Magician:
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. :fearful:

6

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.

7

Grumpy_Mike:
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?

8

I feel a "magic smoke" answer coming

9

The real reason is that it reverse biais the input diodes and causes the semiconductor to break down causing permanent damage.
Not just the arduino anything that wasn't designed to take a voltage outside its supply rails.

10

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 ?

11

MarkT:
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.

12

An RLC is not very controlable in terms of voltage depending on what you do to it. A collapsing magnetic field can create much higher voltages than you supply it with. I would put lots of protection on it. Also you will have to ensure that your potential divider uses high values that the R in the circuit you are measuring.

This sounds like an assignment!