ATTINY85 sleep mode with pin change interrupt

Projects Programming
1

I'm trying to use the ATTINY85 sleep mode, and have it wake up using the pin change interrupt. I'm using Nick Gammon's example code

// ATtiny85 sleep mode, wake on pin change interrupt demo
// Author: Nick Gammon
// Date: 12 October 2013

// ATMEL ATTINY 25/45/85 / ARDUINO
//
//                  +-\/-+
// Ain0 (D 5) PB5  1|    |8  Vcc
// Ain3 (D 3) PB3  2|    |7  PB2 (D 2) Ain1
// Ain2 (D 4) PB4  3|    |6  PB1 (D 1) pwm1
//            GND  4|    |5  PB0 (D 0) pwm0
//                  +----+

#include <avr/sleep.h>    // Sleep Modes
#include <avr/power.h>

const byte LED = 3;  // pin 2
const byte SWITCH = 4; // pin 3 / PCINT4

ISR (PCINT0_vect) 
 {
 // do something interesting here
 }
 
void setup ()
  {
  pinMode (LED, OUTPUT);
  pinMode (SWITCH, INPUT);
  digitalWrite (SWITCH, HIGH);  // internal pull-up
  
  // pin change interrupt (example for D4)
  PCMSK  |= bit (PCINT4);  // want pin D4 / pin 3
  GIFR   |= bit (PCIF);    // clear any outstanding interrupts
  GIMSK  |= bit (PCIE);    // enable pin change interrupts 
  
  }  // end of setup

void loop ()
  {
  digitalWrite (LED, HIGH);
  delay (500); 
  digitalWrite (LED, LOW);
  delay (500); 
  goToSleep ();
  }  // end of loop
  
  
void goToSleep ()
  {
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  ADCSRA = 0;            // turn off ADC
  power_all_disable ();  // power off ADC, Timer 0 and 1, serial interface
  sleep_enable();
  sleep_cpu();                             
  sleep_disable();   
  power_all_enable();    // power everything back on
  }  // end of goToSleep

This all works fine - when I take the switch pin low, it wakes up, flashes the LED, then goes back to sleep again. However, if the switch pin is held low, the ATTINY continues to draw current of about 0.15mA - I presume because current is flowing through the internal pullup resistor. I guess that normally you would just have a kind of push button switch so that a momentary press caused the ATTINY to wake up, and current was only drawn while the switch was pressed. But I want to be able to have the switch go low, and stay low after the ATTINY goes back into sleep mode, but without current then being drawn (and so it's woken up next time by the switch going high.) Is there a way of doing this?

2

You could disable the pullup prior to sleeping with a digitalWrite(switch_pin, LOW); command.

Just make sure to set it back to high when you wake up.

3

Hi,
I am also experimenting with this example and it does not seem to run as expected. I've put few commands to flash the led twice in ISR to see that pin change interrupt has actually worked. When I ground PB4, the led goes on and stays on regardless if I remove ground from PB4 or keep it there. I would expect, that the led flashes twice each time I connect PB4 to ground or disconnect from ground.

// ATtiny85 sleep mode, wake on pin change interrupt demo
// Author: Nick Gammon
// Date: 12 October 2013

// ATMEL ATTINY 25/45/85 / ARDUINO
//
//                  +-\/-+
// Ain0 (D 5) PB5  1|    |8  Vcc
// Ain3 (D 3) PB3  2|    |7  PB2 (D 2) Ain1
// Ain2 (D 4) PB4  3|    |6  PB1 (D 1) pwm1
//            GND  4|    |5  PB0 (D 0) pwm0
//                  +----+

#include <avr/sleep.h>    // Sleep Modes
#include <avr/power.h>    // Power management

const byte LED = 3;  // pin 2 / PCINT4
const byte SWITCH = 4; // pin 3

ISR (PCINT0_vect) 
 {     
  digitalWrite (LED, HIGH);
  delay (500); 
  digitalWrite (LED, LOW);
  delay (500); 
  digitalWrite (LED, HIGH);
  delay (500); 
  digitalWrite (LED, LOW);
  delay (500); 
 }
 
void setup ()
  {
  pinMode (LED, OUTPUT);
  pinMode (SWITCH, INPUT);
  digitalWrite (SWITCH, HIGH);  // internal pull-up
  
  // pin change interrupt (example for D3)
  PCMSK  |= bit (PCINT4);  // want pin D3 / pin 2
  GIFR   |= bit (PCIF);    // clear any outstanding interrupts
  GIMSK  |= bit (PCIE);    // enable pin change interrupts 
  
  }  // end of setup

void loop ()
  {
  digitalWrite (LED, HIGH);
  delay (500); 
  digitalWrite (LED, LOW);
  delay (500); 
  goToSleep ();
  }  // end of loop
  
  
void goToSleep ()
  {
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  ADCSRA = 0;            // turn off ADC
  power_all_disable ();  // power off ADC, Timer 0 and 1, serial interface
  sleep_enable();
  sleep_cpu();                             
  sleep_disable();   
  power_all_enable();    // power everything back on
  }  // end of goToSleep