IEEE Spectrum - North American - March 2014 - 26

and 10.16 mm long. The legs that come with the
kit are purely cosmetic, but not so the board that
takes the place of the standard ceramic packaging. Much sturdier than a typical printed circuit
board, this board doesn't replicate the internals
of a 555 IC in every detail. However, it's divided
into areas that do correspond to the functional
blocks that make up an actual 555, such as the
threshold comparator or the flip-flop that's the
cornerstone of the timer's operation.
Populating the circuit board with its 26 transistors (split evenly between npn- and pnp-type)
26

MAr 2014

NorTH AMerIcAN

and 16 resistors is a straightforward bit of soldering. Threaded screws accommodate leads
to connect the Three Fives kit to the rest of a circuit (there are also holes provided for soldering
leads permanently to the board).
The kit is designed to be a "drop-in" replacement for the 555 chip in existing circuit designs, with the caveat that an extra resistor is
needed for one pin in some circuits operating above 6.5 volts. After building the trial circuit suggested in the kit instructions-an LED
blinker-I tested this drop-in idea with a small

sPecTruM.Ieee.orG

stephen cass (4)

Drop In, turn on: A test circuit I'd previously
constructed [above] uses a 555 IC to generate a
square wave [top left]. Replacing the IC with the
Three Fives model, made of discrete components
[top], via leads poked into the IC socket produced
an almost identical waveform [bottom left].

9-V audio-frequency generator I'd built
some time ago for troubleshooting circuits. Controlled via a variable resistor,
the generator produces square waves
between 5.5 and 7.3 kilohertz.
Using my oscilloscope, I measured
the generator's maximum and minimum output with its normal 555
chip, and then pried the chip out of its
socket. With leads running from the
Three Fives kit poked into the bare
socket holes, I reran the measurements. The frequency of the output
between the chip and the kit matched,
as did the shape of the waveforms,
albeit with a tiny bit more "ringing"
with the kit when the waveform went
from a low to a high state.
The 555 kit would be an excellent
introduction for electronics beginners learning how to solder-detailed
instructions and soldering tips are
given in the accompanying leaflet-
while introducing them to the basics
of integrated circuit design and use.
It also offers opportunities for more
advanced students, by exposing the
internal components of what's normally a black box (a complete circuit
diagram is available on a data sheet
you can download from Evil Mad Scientist's website). With an oscilloscope,
you can probe each block of the timer
as inputs such as the trigger, threshold,
and control voltage are varied, demonstrating how they combine to produce various
outputs. A useful class exercise might be finding
component substitutions or augmentations to
optimize this most general-purpose of circuits
for specific tasks.
For myself, I hope this opens the door to more
kit makers taking integrated circuits out of their
black boxes and making them commercially
available. The first microprocessor, the 4004,
was built from 2300 transistors-no small soldering job, but surely doable over the course of
a season. -Stephen CaSS

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Table of Contents for the Digital Edition of IEEE Spectrum - North American - March 2014