Friday, February 20, 2009

1Hz Clock Generator using PIC12F675

Based on the idea from have created a 1Hz Clock Generator. I use PIC12F675 as it's available locally. Its price is just about US$1.
The concept is using 32.768kHz crystal as a clock for the PIC. Therefor, the internal instruction clock is 32768/4 = 8192 Hz. By using the 16 bit Timer1 to count the instruction clock cycles, the interrupt will occur every 8 second. This period can be reduced by setting initial value of the Timer1 (TMR1H:TMR1L). I have to make Timer1 to count up to 8192 for generating overflow interrupt every 1 second. To make Timer1 count up to 8192, the initial value of TMR1 must be 65536-8192 = 57344 or 0xE000. This means TMR1H = 0xE0 and TMR1L = 0x00. In this case, I need to set only the TMR1H=0xE0 and let TMR1L runs continuously. By changing the initial value of Timer1, I can generate almost any frequencies.

An application for this project is a precise 1Hz blinking LED signal :) ha ha. I know that it's not useful but I think it's fun to look at (am I crazy?). Another application is a precise 1Hz time base for a clock.

The source code is written in MikroC.

// PIC12F675
// 1Hz Time Base Osc.
// Timer1 Module
// 32.768 KHz
unsigned short tick;
void Init ();
void interrupt ()
        if (PIR1.TMR1IF)
                TMR1H = 0xE0;
                PIR1.TMR1IF = 0;
                tick = 1;
void main ()
        tick = 0;
        //Initialize Ports and Timer1 Module
        Init ();
        while (1)
                if (tick)
                        tick = 0;
                        GPIO = (1 << 2);
                if (TMR1H > 0xF0)
                        GPIO = 0;
void Init ()
        TRISIO = 0;
        //Make all pins as output ports
        GPIO = 0;
        //Use Timer1 module
        INTCON.GIE = 1;
        INTCON.PEIE = 1;
        T1CON = 0x01;
        //Overflow every 8192
        TMR1H = 0xE0;
        TMR1L = 0x00;
        //  Enable TMR1 interrupt
        PIE1.TMR1IE = 1;

The schematic is as the following image.
1Hz Clock generator using PIC12F675

The PCB:

3D version:


solarwind said...


dmuse said...

Nice post. What programs do you use for the schematic capture, PCB layout and the 3D view? Thanks.

creativelectron said...

good work !
which software do you use for 3d diagrams ?

Ramesh said...

Nice post! Is it possible to drive the stepper motor of a quartz analog clock, using this 1Hz clock generator?

If yes, please post the modifications.

Really appreciate, if you could share any idea that how do we implement an hourly clock striking using a microcontroller and a audio re-recordable chip???

dom said...

anyone got the hex