Improvising a 555 timer using an ATTiny85
In short, I needed a 1Hz timer for a shift register project and didn’t have any timing ICs around, so I improvised using an ATTINY85. The datasheet 1 in section 12.2.2 says that Timer/Counter1 can be used in PWM mode with two outputs, one normal and one inverted:
Figure 1 - Timer1 in PWM mode with output pairs.
This was exactly what I needed for clocking the shift register I was using (74HC595) that had shift and storage clocks.
#define F_CPU 1000000UL
#include <avr/io.h>
static void ConfigurePWM( void )
{
/* Reset counter */
TCCR1 = 0U;
/* PB4 = PWM output, PB3 = PWM inverted output */
DDRB |= ( 1U << 4U );
DDRB |= ( 1U << 3U );
/* Clear timer on compare match,
* PWMA enable,
* Toggle OC1A output line,
* Precale clock CK/8192
*/
TCCR1 = 0xDE;
/* PWMB enable,
* Toggle OC1B output line
*/
GTCCR = 0x50;
/* 1MHz / 8192 / 122 ~= 1Hz */
OCR1A = 61U;
OCR1B = 61U;
OCR1C = 122U;
}
void main( void )
{
ConfigurePWM();
while( 1 );
}Using a logic analyser this is what it looks like on the output:
Figure 2 - Logic analyzer output from the ATTiny85 connected to PB3 and PB4 displaying a 1Hz signal