Current-voltage conversion stage in prototyping board

ParaDecirAdios · **Joined:** Sat Jun 11, 2011 7:58 am **Posts:** 16

Hello, I am trying to measure a DC current of between 0 to 0.5A using the prototyping board. I connect the +ve wire to the I-V convertor input and the -ve wire to ground.

Here is my code:

Code:

#define RESISTANCE 0

void setup() 
{ 
  // Init USB 
  USB.begin(); 
  SensorProto.setLoadResistor(RESISTANCE);
} 
 
void loop() 
{ 
  USB.println(analogRead(ANALOG4),DEC); 
  delay(1000);
} 

1 - Without any wire connection to ANALOG4, I measure the I-V convertor output using a multimeter. It is 1.2V. But when I set RESISTANCE to 0, 10, 100, and re-program the Waspmote, the output is the same. Is this correct, or am I making a mistake?

2 - If I know that the input DC current is between 0 to 0.5A, and I want to connect the I-V convertor output to ANALOG4 using a wire, what value of RESISTANCE do you recommend?

3 - If I connect the I-V convertor output to the ANALOG4 input, will the voltage be exceeded?

4 - If I connect the I-V convertor output to ANALOG4 and set RESISTANCE to R, what is the formula to convert from ANALOG4 reading to input current?

Muchas gracias!

ParaDecirAdios · **Joined:** Sat Jun 11, 2011 7:58 am **Posts:** 16

Also, if you have any other tips on how to measure an input DC current from 0 to 0.5A using the prototyping board only, please share also.

libelium-dev · **Joined:** Mon Sep 28, 2009 1:06 pm **Posts:** 7440

Hi ParaDecirAdios,

That converter is not the best option for your current range, since you would need a 6ohm resistor to fit the 3.3V input range of the analog pins and that is much lower than the one you can get.

In your case, since you won't need to amplify your output, the first thing to try is just converting that current into a voltage using that 6ohm resistor before the analog pin you select (or the ADC of the prototyping board, if you need more precision).

By the way, which is the source of the current you want to measure? It will help to know its characteristics to be able to help you.

Regards.