This second version is based around a PIC16F628A running at 4MHz to control the display, it also uses a DS1307 realtime clock chip to do the timekeeping. Every second the DS1307 sends a pulse to the PIC chip, the PIC then reads the internal time from the DS1307 over the I2C bus and then displays the time in binary on the LED display.
The bottom row of LEDs display the seconds, the middle rows shows the minutes and the top row is for hours. The time displayed in the picture is 01100:010011:011011 or in decimal 12:19:27. The time is in 24 hour format so goes up to 10111:111011:111011 or 23:59:59
The PCB could be made double sided, or as I have done here single sided with 7 wire links soldered in place instead of the top copper layer. It has a 5 volt regulator so could be powered from any 9 - 15 volt DC power supply.
Step 1: Parts / Tools
1x PIC16F628A & programmer
1x DS1307 realtime clock chip
1x 32.768kHz watch crystal
3x BC548 (or similar) transistor
2x PTM pushbuttons
1x 78L05 regulator
2x 220uF electrolytic capacitors
17x Surface mount LEDs
1x DC power jack socket
5x 4.7K surface mount resistors
8x 100 ohm surface mount resistors
1x 2k surface mount resistor
12x zero ohm links (Or 11 zero ohm links and CR2016 backup battery)
1x 100nF surface mount capacitor
50cm single stranded bell wire
1x 9v - 15v DC power supply with DC jack
Step 2: Make PCBs & Program PIC
The display PCB uses exclusively surface mount devices while the main clock PCB uses a mixture of surface mount and through-hole components.
It is important to program the PIC chip with the hex file prior to soldering into the circuit as there are no ICSP connections on the board.
Step 3: Solder Bottom Components
Step 4: Solder Top Components
Step 5: Solder Display
The display board shown here is a newer version than is used in the rest of the photos in this instructable, it has fewer resistors so is easier and cheaper to make.
Care must be taken when mounting the zero ohm links (resistors with zero resistance) as there are tracks on the PCB running between the 2 solder pads, the links must be positioned so that neither of the metal terminals touch the PCB track between the pads.
Step 6: Finish
The PSU needs to be at least 9v DC and need only be rated at about 200mA or so, the centre connector of the DC jack needs to be positive and the outer should be 0v.
Once the power is connected the clock should display 22:03:00 and immediately start counting the seconds. Then all that is left is to set the time, one of the buttons is used to set the minutes and the other sets the hours, as soon as either button is pressed it sets the seconds to 0 and increments the corresponding display by 1.