# ATTINY85 Timer Questions

#### fredric58

Joined Nov 28, 2014
252
Hello, These questions are based on a project that originated and was constructed and credited to Mr. Nick Gammon. February 2014 entitled "ATtiny85 Torch Locator", Used in the event of a power outage to find a flashlight. "The device powers down for 2 seconds until woken up by the WDT. Then it does a ADC read (analog read) of the LDR (light dependent resistor) to see if it dark or not. If it is not dark it goes back to sleep."

This is great if being used in a power outage situation. If the desire is simply to determine whether it is day or night. QUESTION 1: Is it possible and would it conserve any power to have it do the analog read every 5 minutes or say every 15 minutes or even every half hour?

"If it is dark, then the code turns timer 0 back on (so that millis() will work) and then turns on the LED, waits 2 mS, and turns it off again. This brief flash is plenty to spot the LED in the dark."

QUESTION 2: Is it possible to turn the LED on for 15 - 30 seconds, wait 5 minutes, repeat, until Light?

I have just begun learning about Low Power, Timers and their limitations.

Thank you. I hope this is posted in the right place and format, and direct!

Code:
// ATtiny85 torch detector
// Author: Nick Gammon
// Date: 25 February 2015

// ATMEL ATTINY 25/45/85 / ARDUINO
// Pin 1 is /RESET
//
//                  +-\/-+
// 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
//                  +----+

/*

Pin 2 (PB3) <-- LDR (GL5539) --> Pin 7 (PB2) <----> 56 k <----> Gnd

Pin 5 (PB0) <---- LED ---> 100 R <-----> Gnd

*/

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

const byte LED = 0;          // pin 5
const byte LDR_ENABLE = 3;   // pin 2
const byte LDR_READ = 1;     // Ain1 (PB2) pin 7
const int LIGHT_THRESHOLD = 200;  // Flash LED when darker than this

// when ADC completed, take an interrupt

{

// set a2d prescale factor to 128
// 8 MHz / 128 = 62.5 KHz, inside the desired 50-200 KHz range.

if (port >= A0)
port -= A0;

#if defined(__AVR_ATtiny85__)
ADMUX = (port & 0x07);  // AVcc
#else
ADMUX = bit (REFS0) | (port & 0x07);  // AVcc
#endif

noInterrupts ();
set_sleep_mode (SLEEP_MODE_ADC);    // sleep during sample
sleep_enable();

// start the conversion
interrupts ();
sleep_cpu ();
sleep_disable ();

// reading should be done, but better make sure
// maybe the timer interrupt fired

// ADSC is cleared when the conversion finishes
{ }

return (high << 8) | low;

// watchdog interrupt
ISR (WDT_vect)
{
wdt_disable();  // disable watchdog
}  // end of WDT_vect

#if defined(__AVR_ATtiny85__)
#define watchdogRegister WDTCR
#else
#define watchdogRegister WDTCSR
#endif

void setup ()
{
wdt_reset();
pinMode (LED, OUTPUT);
pinMode (LDR_ENABLE, OUTPUT);
power_all_disable ();  // power off ADC, Timer 0 and 1, serial interface
}  // end of setup

void loop ()
{
// power up the LDR, take a reading
digitalWrite (LDR_ENABLE, HIGH);
// power off the LDR
digitalWrite (LDR_ENABLE, LOW);

// if it's dark, flash the LED for 2 mS
if (value < LIGHT_THRESHOLD)
{
power_timer0_enable ();
delay (1);  // let timer reach a known point
digitalWrite (LED, HIGH);
delay (2);
digitalWrite (LED, LOW);
power_timer0_disable ();
}

goToSleep ();
}  // end of loop

void goToSleep ()
{
set_sleep_mode (SLEEP_MODE_PWR_DOWN);
noInterrupts ();       // timed sequence coming up

// pat the dog
wdt_reset();

// clear various "reset" flags
MCUSR = 0;
// allow changes, disable reset, clear existing interrupt
watchdogRegister = bit (WDCE) | bit (WDE) | bit (WDIF);
// set interrupt mode and an interval (WDE must be changed from 1 to 0 here)
watchdogRegister = bit (WDIE) | bit (WDP2) | bit (WDP1) | bit (WDP0);    // set WDIE, and 2 seconds delay

sleep_enable ();       // ready to sleep
interrupts ();         // interrupts are required now
sleep_cpu ();          // sleep
sleep_disable ();      // precaution
}  // end of goToSleep

#### Wolframore

Joined Jan 21, 2019
2,610
yes and yes.

#### fredric58

Joined Nov 28, 2014
252
Thank you, so on part 1. Ex: 10 minutes from the WDT ???

Code:
// sleep for a total of 600 seconds
int i;
for (i = 0; i <=75; i++)
{
myWatchdogEnable (0b100001);  // 8 seconds