Arduino output gives only 3V

Hello,

I have just hooked up my arduino to a HC-05 bluetooth module and i have programmed it in such a way that if the the bluetooth receives a 1, it should send a HIGH to pin and if it receieves a 1 again, it should LOW to the pin.

I checked the voltage of the output and it shows only 3.2 V. When i write a simple program to just send HIGH to a pin, I can see that the output is 5V.

Appreciate your help here !

int led1 = 7;
int led2 = 8;
boolean led1_state = LOW;
boolean led2_state = LOW;
void setup()
{
  Serial.begin(9600);
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
}

void loop()
{
  if (Serial.available()>0)
  {
    int value = Serial.read();
    if (value == '1')
    {
      if (led1_state == LOW)
      {
        digitalWrite(led1, HIGH);
        led1_state = !led1_state;
        return;
      }
      else
      {
        digitalWrite(led1, LOW);
        led1_state = !led1_state;
      }
    }
    
    if (value == '2')
    {
      if (led2_state == LOW)
      {
        digitalWrite(led2, HIGH);
        led2_state = !led2_state;
        return;
      }
      else
      {
        digitalWrite(led2, LOW);
        led2_state = !led2_state;
      }
    }
   }
}

What are you using to power your Arduino, USB?

I’m not sure how much current the HC-05 draws but it may be too much and as such your voltage could be dropping.

i use a 5V external power source. How do i find out how much the HC-05 is drawing?

You measure amps (mA in this case) in series with it. You may have to change the positive lead of your multimeter to another jack type port. Read your multimeter instructions if it's first time measuring current draw.

Firstly, is the 5V source plugged into the barrel jack or the 5V pin?

If you have 5V going into the barrel jack then that right there is you problem. The barrel jack needs to be at least 7.2V or so to get a stable 5V output as there are diode drops etc.

Secondly, you could either measure the current draw with a multimeter in series with part or find a datasheet specifying current draw. I recommend looking up datasheet if you have never measured current draw before, you might blow a fuse in the multimeter if not careful.

In order to read the current draw of a circuit, you need to use your (common) multimeter on the "10ADC" range where you have to change the positive lead on the meter. If you use any other range, the resistance of the meter will substantially drop the voltage to the circuit which will then not be operating correctly so any reading will not be valid.

Paul__B: In order to read the current draw of a circuit, you need to use your (common) multimeter on the "10ADC" range where you have to change the positive lead on the meter. If you use any other range, the resistance of the meter will substantially drop the voltage to the circuit which will then not be operating correctly so any reading will not be valid.

HUH?

To measure 5A you use the 10A range/terminal to measure 10mA use the mA range to measure 10uA use the uA range

The series resistance is only an issue if you are trying to measure a current that varies by many orders of magnitude (such as sleep-mode supply current), in which case the solution is to bypass the meter with a switch to short it out while changing ranges.

You are entitled to your opinion.

I have two of the more common sorts of multimeters here, one conveniently fitted with clip-leads (purchased from eBay).

So I clipped them together, set one to the 200 ohms range and the other to 200 mA. The ohms range reads 8.7 and the mA, about 1 mA. Interesting.

Let's say your Arduino draws 100 mA and you read it on the 200 mA range, putting the meter in series with a 5V supply. According to my comprehension of Ohm's Law, 100 mA through 8.7 ohms represents a drop of 0.87 volts, so the Arduino is now operating from only 4.13 volts instead of 5. You may consider that irrelevant, but I do not. But then, that's just my opinion.

Hi,

I have attached my schematic. A pretty basic circuit…

Btw, my input V is only 5V via the barrel jack. Could that be the problem?

Where are your series led resistors?

ajaynmoorthy: Btw, my input V is only 5V via the barrel jack. Could that be the problem?

Just to reiterate:

Posted by: wes000000: if you have 5V going into the barrel jack then that right there is you problem. The barrel jack needs to be at least 7.2V or so to get a stable 5V output as there are diode drops etc.