Help with MAX471 current sensor.

Hello, I'm testing the MAX471 current sensor, i' m using this code found in "Henry's bench" website, and modified a bit to give me mAmps.

// Henry's Bench
// MAX471 Power Meter Tutorial

#define VT_PIN A0 
#define AT_PIN A1

void setup()

void loop()
  int vt_read = analogRead(VT_PIN);
  int at_read = analogRead(AT_PIN);

  float voltage = vt_read * (5.0 / 1024.0) * 5.0;
  float current = (at_read * (5.0 / 1024.0))*1000;
  float watts = voltage * current;
  Serial.print("V: "); 
  Serial.print(voltage, 3);
  Serial.print("\tmA: ");
 // Serial.print("\tWatts: ");
 // Serial.println(watts,3);

Now I connect a DC motor (a standard disk drive one) via a 200 Ω resistor I'm powering the motor from arduino uno 5V pin connected to a laptop. (no external power supply)

and I get readings V ~ 5 - 4.4 and mA ~ 9.8 - 20.0

Can someone confirm that this motor draws only about 20mA ?


I tested it with my multimeter and it seems ok.

By the way how to delete my posts if i want in this site, and why there is this weird limitation to edit posts only every 5 minutes?