LED Binary Clock

Step 2: Make PCBs & Program PIC

The first step is to make the PCBs, the PCB layout and schematics for the main clock and the display board are provided in Eagle format. The clock PCB is double sided, but the top layer consists simply of 7 links, this means that the PCB could also be made as a single layer with 7 wire links instead, this is the way I chose to make it as I cannot make double sided boards.

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.

Comments

[botronics]

I would like to make this small enough to make a pocket watch out of it. To save power, is there a way to have the leds come on only when needed? Maybe this would work: If power to the pic only is left off, will the correct time show when the pic is turned on for a moment? While all the time the DS1703 is always running in the background to keep the time base.

[shuttleu93]

could you please draw up the schematic so it is easier to read please?

[ElevenOf9]

Hi,

The schematic files were available in the zip files, but I have also uploaded them now as images to the instuctable for easier viewing.

[dava_2]

.sch file isn't working with my software: ExpressSCH .

I what soft was made this .sch?

[ElevenOf9]

Hi, it was made in Eagle

[dava_2]

Thank you, works now!

[lachlanmiller]

Could you clarify the concept of operation, i don't understand, how you are able to individually address each led from the pic, im assuming that you dont need to, and with this combination at any given time, you can turn on the required combination of led's to display the time.

could you explain this a little ?

[ElevenOf9]

Hi,

The LEDs are multiplexed, so at any given time only 1 row is illumiated, the PIC is constantly turning each row on and off so fast that it looks as though all 3 rows are illuminated at the same time. All 17 LEDs are controlled by 6 data lines and 3 address lines.

First of all the PIC loads the data for the seconds into PORTB, it then sets the address line for the seconds row high (turning on the LEDs) after a very brief pause it sets the address line for the seconds row low (turning off the LEDs). Then it loads the data for the minutes row into PORTB, turns on the minutes address line, paues, then turns it off again. The hours are displayed in the same way, then the whole process starts again.

A good visual example of how to multiplex LEDs can be found here:  http://www.franksworkshop.com.au/Electronics/RGB/RGB.htm

I hope this helps.

[drj113]

A technique I have used when there are no ICSP connections, is to use a short ICSP header cable, directly soldered onto the appropriate pins.  That has saved me *many* times :-)