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Big LED Clock

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Big LED Clock


Updated: 10/10/08
I finally got around to fixing the firmware to correctly display everything. The AM/PM function now works and the time setting accounts for the day have 24 hours in it. The updated software can be found down at the bottom of the page.

Clock Home

Here is a shot of the clock in its new home. It is ready for years of faithful service. Please ignore the flower pillow. Blame that one on my wife.


As with most electronics projects that I undertake, this project was inspired by a Project that was done elsewhere on the internet on a site that appears to have vanished into thin air. I liked the idea of having a big clock thermometer so I decided to build one for myself. It had to be sleek, stylish, accurate and functional. I broke the design in to three boards to allow for easier creation of the sub components. At the time when I created the clock it seemed like a logical idea. To make life easier is used a serial LED drive from Maxim that took the display scanning responsibilities off of the microcontroller. The RTC is a DS1304 again from Maxim and the temperature sensor is a one wire interfaced DS18B20 from Maxim. (Maxim gives out free samples and I did this project while I was still in college)

Clock Prototype

Before the project went forward I wanted to make sure that the design would be feasible. I breadboarded up the thermometer portion of the circuit. The display was replaced with a regular height 7-segment display. The UCN5832A from Maxim. This chip gives the ability to drive 32 leds from a 3 wire serial interface. The UCN5832A is a low side drive so it is required to use the proper LED display. The two DS1820s worked great. There interface is simple but gives 0.5C accuracy from some crazy range that would fry a person anyway.

Clock Face

The clock face was drilled in a clock pattern and 5mm leds were hot glued into the holes. The letters on the left hand side represent Indoor, Outdoor, Celsius, Fahrenheit, AM and PM.

Clock Face - LEDs

Each 7 segment display consisted of 7 segments with 6 LEDs per segment. The LEDs for each segment were wired in series and driven from a 12Vdc source. At this point the clock looked like a bed of nails and more then once I was stabbed by the LED leads. Wiring up all those LEDs was a pain but the result was well worth the pain.

Wiring and Hot Glue

Time, patience and LOTS of hot glue go us to the point were it was starting to look like a clock. The three boards are mounted on 10-32 screws that were hot glued to the clock face to act as stand-off. It was kind of ghetto but it got the job done. The boards, from left to right are: the letter control board, the display control board and the microcontroller board.

Almost there...

Even before it was turned on it looked cool. The light shines through the LEDs giving a good impression of what the display will looked like turned on. The missing tooth on the "F" was because I miss drilled one of the wholes to big. This picture was taken before the LEDs were wired up so it fell out while taking the picture. It was replaced before the Hot Glue was attached.

Clock Controls

Here is what the back looked like after everything was loaded into it. The wiring wasn't pretty. I reused a lot of stuff that I found lying around. Remember this was a budget college project.

Clock Controls

The clock is controlled via 4 SPST switches and 2 momentary switches. The SPST switches are used to control what is display and how it is displayed. The 2 momentary switches are used to set the time.

It is Alive...

After much sweet and tears (not really) the clock finally takes life. Here is a shot of the time display on the clock.

What Temperature is it?

I will tell you what temperature it is, just let me look at my clock here. It is 27C right now.

It actually works!!!

Here is a quick video of the clock showing both time and temperature in both C and F. It still needs a little love but is done for now...

Big LED Clock code and schematics

If you ask really nicely I can probably find the PCB files for this project.

This information is supplied in the hope it may be useful but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.

Web site and all contents Copyright Steven Easley 2005-2008, All rights reserved.