On the internet there are so many Led Flasher’s projects, some even with low current consumption, but what I needed was a flasher to be used for geocaching, extremely small and that could last at least one year with a button battery.
I started so a little experiments with the ATtiny85 low power modes using the sketch of insidegadgets, achieving a power consumption of about 4.5uA in standby and of about 3mA during the led flash that occurs every 4 seconds and lasts for about 30ms.
In this way, the average consumption is around 25uA, which with a CR2032 button battery from about 220mAh, this means about a year of life!
After a first draft of the project, I thought it might be useful to also have a 12V version so that it can be also powered by the battery of a car.
Here you can see the circuit on the first version, namely the one powered by 3V button battery:
The schematic is really very simple because the real work is done by the code:
/*
Ultra Low Power Led Flasher
with AtTiny85 @ 1Mhz
by Luca Soltoggio
06/01/2014
http://www.arduinoelettronica.com
*/
#include <avr/sleep.h>
#include <avr/wdt.h>
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif
int pinLed = 4;
volatile boolean f_wdt = 1;
void setup(){
pinMode(pinLed,OUTPUT);
setup_watchdog(8); // approximately 4 seconds sleep
}
void loop(){
if (f_wdt==1) { // wait for timed out watchdog / flag is set when a watchdog timeout occurs
f_wdt=0; // reset flag
digitalWrite(pinLed,HIGH); // let led blink
delay(30);
digitalWrite(pinLed,LOW);
pinMode(pinLed,INPUT); // set all used port to intput to save power
system_sleep();
pinMode(pinLed,OUTPUT); // set all ports into state before sleep
}
}
// set system into the sleep state
// system wakes up when wtchdog is timed out
void system_sleep() {
cbi(ADCSRA,ADEN); // switch Analog to Digitalconverter OFF
set_sleep_mode(SLEEP_MODE_PWR_DOWN); // sleep mode is set here
sleep_enable();
sleep_mode(); // System sleeps here
sleep_disable(); // System continues execution here when watchdog timed out
sbi(ADCSRA,ADEN); // switch Analog to Digitalconverter ON
}
// 0=16ms, 1=32ms,2=64ms,3=128ms,4=250ms,5=500ms
// 6=1 sec,7=2 sec, 8=4 sec, 9= 8sec
void setup_watchdog(int ii) {
byte bb;
int ww;
if (ii > 9 ) ii=9;
bb=ii & 7;
if (ii > 7) bb|= (1<<5);
bb|= (1<<WDCE);
ww=bb;
MCUSR &= ~(1<<WDRF);
// start timed sequence
WDTCR |= (1<<WDCE) | (1<<WDE);
// set new watchdog timeout value
WDTCR = bb;
WDTCR |= _BV(WDIE);
}
// Watchdog Interrupt Service / is executed when watchdog timed out
ISR(WDT_vect) {
f_wdt=1; // set global flag
}
The complete project, 3V and 12V dual-use version can be found on Fritzing posted to the following address:
http://fritzing.org/projects/ultra-low-power-led-flasher-with-attiny
See you soon!
