BY JOE DeMEYER
I Googled “intervalometer” and
found a few commercially built units.
Many were for laboratory use, and a
few were for specific cameras. The
most intriguing and flexible was the
Time Machine (
/photo/ camctlr.html). It had great features including motion sensor inputs,
and a range of interval setups from
simple to complex. However, it did not
interface to my camera and was more
than I wanted. Something about the
Time Machine’s package reminded
me that I had built a cookie timer with
a BASIC Stamp a few years ago.
At the Parallax website, I reviewed
the BASIC Stamp, but thought I might
require more program space and
memory for my project. This led me to
consider the SX microcontroller. After
I read about other SX projects, I felt
that it would be a platform I could
use now and in the future! In addition
to a free compiler, the price for
the prototyping board made it very
attractive to start experimenting.
Intervalometer (picture triggered)
taking pictures at a certain time of day
and stop a few hours later. For example,
the intervalometer should start triggering pictures of a sunrise at 4 AM and
stop at 8 AM. With a timed session, I
could set the start time the night before.
When I return the next morning, the
camera and intervalometer would have
captured the sunrise (I called this the
Delay mode). In addition, I wanted to
be able to start taking pictures immediately and continue for a set period of
time (I called this the Now mode).
In order to make my intervalometer field programmable, I selected a
four direction switch and an LCD
screen. I used the switch to navigate
and select options from a menu
presented on the screen.
The final design included a Parallax
SX- 48, a DS1302 Real Time Clock (RTC)
with battery back-up, optocouplers, and
menu-driven interface presented on a
screen. I considered using the SX- 48’s
real time clock counter for timed
sessions. This would have required
some familiarity with interrupts. Since
this was my first project with the SX- 48,
I decided to use the RTC.
After completing the design, I
placed a graphic of the SX- 48 Protoboard
into a Word document. Using items from
■ FIGURE 2. Power Budget. I estimated
the power consumption from
specifications of the components. At
the end of the project, I measured the
the Word Drawing toolbar, I laid out
components onto the graphic. When I
was done, I was confident they would fit
on the Protoboard (see Figure 1).
As a final step before starting, I
estimated power requirements. When
the project was complete, I measured
the current required for the circuit
quiescently and in operation. The
results are in Figure 2.
In addition to setting the interval
between pictures, I wanted to specify
when to start and stop taking pictures.
I also wanted to program these
functions in the field.
The number of pictures — or frames
— per time period varies based on the
event. Longer events, such as a change
in season, require one frame per day
where a blooming flower requires two
frames per minute (frames/min). I
planned to use the intervalometer for
events that last from 24 to 48 hours so
I specified the slowest rate as one frame
per minute. My camera required some
time to recover between pictures, so
my highest rate was 20 frames/min.
In some cases, I wanted to start
I believe in breaking down a large
project into small chunks. For the circuit
construction, I installed components on
the Protoboard and made a few small
programs to help evaluate their operation. The simplest place to start was
the LCD. By having a working display, I
thought I would also be able to resolve
programming issues by displaying
information as the program executed.
I soldered a three pin header to the
Protoboard so that power and ground
pins lined up with the Vdd and Vss bus
lines; a third pin would be used to com-
■ FIGURE 3. The back of the front panel
shows how the four-direction switch
was mounted. When the intervalometer
was complete, I thought the switch
connections should have had heat
shrink tubing to help reduce stress.
December 2007 35