project not working when switching to battery power

Question

I have a project which involves a photocell, an led, a push button, and a small hobby servo (tower pro sg5010) - the project works as expected when the arduino is powered by usb, but when I switch to battery power (4 AA batteries) - it doesn't work.

When powered by batteries, the servo actually starts right up and moves to the correct angle, so I feel like it should be getting enough power, but when I push the push button, it doesn't move to the new angle. I can hear a clicking noise of the servo on a regular interval, like a clock, and my LED flickers on and off at about the same interval.

If I'm doing something wrong, can anyone point it out? If it's just that the servo is not getting enough power, is there a way to add a transistor or something so that I don't have to add a separate power supply for the servo (I'm not sure there's room in my project's enclosure).

I've attached a fritzing diagram as well as my project code.

CODE:

#include <Servo.h>

const int buttonPin = 2;     // the number of the pushbutton pin
boolean buttonPushed = false;

const int ledPin =  13;      // the number of the LED pin


const int servoPin = 9;
Servo servo;
int angle = 0;
int servoStartAngle = 90;
int servoEndAngle = 10;

boolean servoActivated = false;

// variables will change:
int buttonState = 0;         // variable for reading the pushbutton status

int photoCellPin = 2;
int photoCellThreshold = 500;
int photoCellActivated = false;


void setup() {
  Serial.begin(9600);
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);      
  // initialize the pushbutton pin as an input:
  pinMode(buttonPin, INPUT);

  servo.attach(servoPin);
  servo.write(servoStartAngle);

}

void loop(){
  // read the state of the pushbutton value:
  buttonState = digitalRead(buttonPin);

  int photoCellVal = analogRead(photoCellPin);

  if (photoCellVal > photoCellThreshold){
   photoCellActivated = true; 
  } else {
   photoCellActivated = false; 
  }

  // check if the pushbutton is pressed.
  // if it is, the buttonState is HIGH:
  if (buttonState == LOW && buttonPushed == false) {     
    // turn LED on:    
    buttonPushed = true;
    Serial.println("button pushed");
  } else if (buttonState == LOW && buttonPushed == true){
   buttonPushed = false;
   Serial.println('deactivate');
  } 



  if (buttonPushed == true){
   digitalWrite(ledPin, HIGH); 
  } else {
   digitalWrite(ledPin, LOW); 
  }

  if (buttonPushed && servoActivated == false && photoCellActivated == true){
    servoActivated = true;
    Serial.println("activate motor");

    for(angle = servoStartAngle; angle > servoEndAngle; angle--){                                  
      servo.write(angle);
      Serial.println(angle);
      delay(15);    
    } 
  } else if (buttonPushed == false && servoActivated == true){ //deactivate
    for(angle = servoEndAngle; angle < servoStartAngle; angle++){                                  
      servo.write(angle);
      Serial.println(angle);
      delay(15);    
    }
    delay(200);
    servoActivated = false; 

  }

  delay(200);
}

Answer 1

You may find that, with a high load on batteries, it's depleting the battery quickly; batteries often recover after a while, which may be confusing things further. Try using a multimeter to measure the voltage on the battery, when your program is running.

The Arduino (actually, the chip that runs the Arduino) has brown-out detection - if the voltage drops below a certain level, the Arduino will shut down; if the power comes back up, the Arduino will start up again - but reset. The chip has settings for 1.8v, 2.7v, and 4.3v brownout detection (or none at all!); something I read on the interweb (if you can trust that) said the default was 4.3v. It may be worth flashing an led on startup, so you can tell when the chip is reset.

Also, if you are powering the Arduino through the voltage regulator (using the power socket on the Arduino), then you need about 6-7 volt in just to get 5 volt at the Arduino - this causes further power loss. If using 4 AA batteries through the voltage regulator, you will get 6 volts (probably a little more when the batteries are fresh) going into the regulator - barely or not quite enough! - and the voltage on the Arduino is likely to be below the 5v it needs. Any load (in one of my projects, two large 7-segment displays) can cause the voltage to drop enough to trigger a reset. If you are using the voltage regulator, check the voltage between the 5V and GND pins.

Answer 2

I had an even simpler project only involving a TMP sensor and 433 MHz RF module. On a 9V (150 mAh) block battery it lasted only about 2,5 hours. The Arduino is great for prototyping this sort of stuff, but when you want to build something for battery operation I found that it draws 56 mA just looping without RF or motor!

Counting 2 digital outputs, 1 digital input and 1 analog input in your project, you can run that of an ATTiny85 or ATTiny45. It's the same family and after setup can be programmed with the Arduino environment. You can also opt for a lower speed bootloader 1 MHz or 8 MHz instead of 16 MHz for the Arduino to save energy, you don't seem to calculate that much. The ATTiny will draw about 10 mA looping this way.

Next you'll find also that you can disable the brown out detection in the bootloader, so it just drains the battery until completion.

Saving space in you enclosure by swapping Arduino board for ATTiny chip will allow you to put in more batteries, say 8 AA in two parallel packs of 6V each.

When that doesn't help you'll discover about the sleep modes and disabling ADC when not in use, where you go to sleep for specific intervals and allow the chip to be woken up by interrupts. In sleep mode I found the ATTiny to consume only 0.03 mA.

Some more information

Program an ATtiny with Arduino

ATTiny files for Arduino IDE