the surrounding light. More information on all these
projects can be found at Instructables.com. The ultra low
power feature of the CSS555 truly excels in projects such
Extended Mode Operation
The second remarkable feature of the CSS555 is that
it is user programmable for extremely long timing periods
— from hours to days — with small value capacitors. The
chip includes an internal counter that tracks the capacitor
charge/discharge cycles and changes the output pin state
when the selected number of cycles has occurred. Figure
6 illustrates this with a counter value of 10.
Selectable counter values go in multiples of 10: from
100 = 1 (the standard 555 mode) up to 106 = 1M. Figure 7
illustrates a monostable circuit set up for a delay of about
16 minutes using a capacitor of only 100 pF (which is built
into the CSS555C variety of the chip).
For the extended functions, access to a programming
board is needed, of which two are available from Custom
Silicon Solutions (CSS; www.customsiliconsolutions.com).
The “EZ Programmer” shown in Figure 8 works from two
AAA cells, reads the current settings on the chip, shows
them via LEDs, and will reprogram the chip according to
the positions selected for the switches. It is extremely easy
to work with this programmer.
The other programmer (a deluxe version) is supplied
in the CSS555C Demonstration Kit. It works through a
computer via USB and the configuration settings can be
selected from drop boxes. The screenshot of this
programming package in use shown in Figure 9 shows
many of the options that are selectable for this timer.
A Practical Application
The following project illustrates a very practical
application of the CSS555 operating in the extended
mode. The 5” battery powered fan in Figure 10 proved
itself well worth the few dollars it cost. Whenever
conditions got a bit warm, I used it on the desk or next to
the easy chair when just a little quiet breeze was all that
was needed to maintain comfort. It was indeed quiet —
especially on the low setting — which seemed to be the
This fan was so quiet, in fact, that more often than
not, I would altogether forget the thing was on and fail to
turn it off. When I’d return to the scene and reach to turn
it on, I would find to my dismay that it was already on, but
with two dead D cells! Reminder notes placed in various
locations proved futile.
After a couple of summers of this, it finally dawned on
me that the CSS555 in extended monostable mode
offered a nice solution to this problem — and a significant
savings in D cell batteries! It could be configured to run
for around 15 minutes after just a touch of a button.
During idle periods, it would consume a negligible level of
power, taking less than a half dozen microamps between
button pushes. Of course, a microcontroller first came to
mind but experience with this fan showed that it could
provide adequate comfort when its series-connected pair
February 2016 35
It also blinks.
FIGURE 4. The CSS555 as the heart of a very efficient
solar engine circuit.
FIGURE 5. “Walker the Robot.” He is energized by the
solar cell on his head.
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