Open-Drain RA4 pin on PIC Microcontroller

I had a problem with RA4 pin which I cound not send '1' nor output 'high' to this pin. After some searches, I have found that RA4 pin (pin 3 for PIC16F627a) is "Open-Drain" type output pin. That means it cannot source current and it will be high impedance when assigned logic '1' to it. I cannot set this pin as an output pin by using 'TRISA=0x00'. The solution is attaching a pull up resistor (10K) to the RA4 pin in order to use this pin as an output pin.

Schematic of 8x8 Led Dot Matrix Clock using PIC16F627A

The above schematic is 8x8 Led Dot Matrix clock using PIC16F627A (or PIC16F628 which is more expensive but larger memory) and a shift register 74HC595. The PIC is running with 4MHz internal oscillator so pin 15 (RA6) and 16 (RA7) are free. Therefore, the PIC16F627a can drive the 8x8 Led Drive matrix with these 2 free pins (RA6, RA7) and RB0-5, . The Timer1 (TMR1) external clock is generated by the watch crystal 32.768KHz + load capacitors 15pF and fed to RB6 and RB7. The pins are used up!. Method of setting time is similar to the 5x7 Led Dot Matrix Clock.

I have intention to make this with SMD components so the 8x8 Dot Matrix will be the biggest component. The whole clock will be just 20x20mm which is small enough to be a small pocket watch or even a wristwatch. The only problem is the power supply.

8x8 Led Dot Matrix Clock using PIC16F627A

Actually, I have made this long before the 5x7 led dot matrix clock. The clock utilizes a PIC16F627A and a 74HC595 to drive a small 8x8 Led Dot Matrix display (20x20mm). My dream is transforming these clocks to watches that I can ware on my wrist.

Where to buy DS1307 RTC

The DS1307 Real Time Clock chip is not so easy to get.

To my knowledge, you can buy the DS1307 from DonTronics

Big 5x7 Led Dot Matrix Clock with new font

Now, I'm so crazy about led dot matrix clocks and led dot matrix watches. Just recently, I have upgraded my small 5x7 Led Dot Matrix Clock with a bigger green 5x7 led dot matrix display and a new font.
For the images below, the time 21:44:37 was displaying on the clock. The clock display is big comparing to a 44mm Panerai (PAM 4).




The code for the new font is showing below:

const unsigned char char2[][4]={
{0x0E,0x11,0x0E,0x00}, //0
{0x09,0x1F,0x01,0x00}, //1
{0x13,0x15,0x09,0x00}, //2
{0x11,0x15,0x0A,0x00}, //3
{0x1C,0x04,0x0F,0x00}, //4
{0x19,0x15,0x12,0x00}, //5
{0x0E,0x15,0x12,0x00}, //6
{0x13,0x14,0x18,0x00}, //7
{0x0A,0x15,0x0A,0x00}, //8
{0x09,0x15,0x0E,0x00}, //9
{0x0A,0x04,0x0A,0x00}, //Comma1
{0x04,0x0A,0x04,0x00} //Comma2
};