(click image for better view)
I wanted to build something I could use daily, for no reason, other
than the satisfaction of building something truly useful. A clock
is a pretty useful appliance. Even though you can purchase one for
a few dollars, how many people can say that they built one that
they use everyday? This is a digital clock built around the picaxe
18X microcontroller and the DS1307 real time clock. Since simply
displaying the time is useful, but really boring, and the
microcontroller has capability to spare, I added a bit of code to
the display section to do some "digit-rolling" animation.
In between displaying the time every second or two, random digits
roll by on the display starting from right-to-left, and then back
to the right again... not only geeky, but artsy too!
The basic hardware has the following features:
- Crystal controlled real-time clock
- LED time display with animation
- time-set buttons
- Battery back-up
Parts and Design
Picaxe 18X microcontroller
HC4 4-digital SPI LED display
DS1307 real-time clock chip
32767 Hz crystal
Picaxe 18x prototyping board
From the pictures, you can see that I built the clock on a Picaxe
18X prototyping board. Purchasing this board and mounting a wireless
breadboard on it was easier than starting with perf board or Vero
(strip) board, and cost only a few dollars more. On the prototyping
board, I socketed the DS1307 with crystal and also a 24LC256 i2c
RAM chip. The RAM is not needed for this project, but at an extra
$0.50, it gives the design significantly more capability. With a
small amount of additional code, this design could become a datalogger.
Or add a piezo, some switches, and some code, and this becomes an
alarm clock. But for now, it is an art clock. See the picaxe
project page for part sources.
BTW, the HC4 is a 4 digit LED display controlled via a serial interface
that was produced in 1985 and ended up as surplus 20 years later.
Unfortunately it looks like it is now unavailable and I'm unaware
of a replacement of similar value, but you could use a serial LCD
display as a simple but more costly replacement. Alternately, you
could get four 7-segment LEDs and roll your own using the MAX7219
display driver, or buy one of the higher-pinout Picaxe controllers
and just control the LED segments directly. Email me if you know
of an inexpensive easily available serially controlled multi-digit
display and I'll list it on my sources page.
Because I don't have the 18X included in my schematic drawing
program, I'll just list the very simple connections that the device
requires. Basically, a 2 line (DAT and CLK) interface between the
18X and HC4 display, and a 2 line (SCL and SLA) interface between
the 18X and the DS1307 are all that are required. When I loaded
the Picaxe code over the serial link, it initialized the DS1307
with the proper time, and a 1.5v battery back up keeps it. But hooking
up 2 N.O. buttons on the 18X and a bit of additional code will allow
the clock to be set without downloading new code via the serial
The software started
out as 2 distinct code pieces; one which reads the time from the
DS1307 via the I2C interface of the 1307, and the other which bangs
bits to display a number on the HC4 display. After a few minutes
of testing to make sure that the code was functioning, it was clear
that the clock should and would need to do something else to make
it "unique"; otherwise it would just be a digital clock...
and you can imagine the passionate responses that would elicit from
onlookers. So the animated random digit display starts at the least
significant digit, creeps across until all digits are changing randomly,
then fixes the digits at the correct time starting with the most
significant digit makes the display a bit more interesting if not
a bit puzzling at first glance.
Like many projects, packaging the device in an aestheticly pleasing
case is challenging, mostly because it takes an equivalent time
as the rest of the project. I'm thinking that an antique steam-punk
style case might look good and be appropriate for the circa 1985
This code is explicitly released under the GPL.
And this page is licensed under a Creative
Commons Attribution 2.5 License.
Write me if you find this project
interesting. Link to this page if you find it relevant..
Warning, building a digital clock is not cost effective over commercial
products. This project is provided without any warranty and probably
isn't suitable for anything.
Read or write a comment on the hardware projects
Back to Picaxe Projects