What is SEQSWITCH?
It is a clever design for a simple "combination" security system
for electrical applications, not based on computer technology, that can be installed to
protect any electrical device, and can be constructed cheaply with only a few switches,
one diode and one relay.
It is named SEQSWITCH because the "combination" to operate it is simply the
sequence in which several switches are operated. If operated in the
correct sequence, the device will operate, otherwise an alarm may be sounded.
Applications that can benefit from using a SEQSWITCH include electrical
door locks, an auto ignition, electrically powered equipment such as a ham radio
But is it practical? Ummm, well,
to be perfectly honest with you, perhaps not. Prior to the invention of
microprocessors and even before integrated circuit chips, this
circuitry might have been really useful in many applications. Now it is probably
more of a hobby or home project with which you can have fun
constructing it and demonstrating it for friends. If you are the type of
experimenter who gains satisfaction from building something whose workings are
clearly understandable, SEQSWITCH may provide just the right project for you.
Functionally, a SEQSWITCH may be represented as shown in Figure 1:
The device to be operated and the alarm device must either both operate at the same
d-c voltage, or a control relay must be provided for one of these devices. The
operating voltage and power consumption will determine the ratings of the components
you use in building the SEQSWITCH.
The SEQSWITCH can be built from commonly available double-pole-double-throw
(DPDT) switches, as many as desired (minimum of three), an inexpensive diode, and a
single-pole-double-throw (SPDT) relay (see PARTS section of these
The switches can be mounted in any physical configuration, either adjacent to
one another on a compact panel, or separated, so that one or more of the switches
are not readily apparent as part of the switch group, for security.
For simplicity in the following explanation and instructions, assume that you are
going to build a 5-switch circuit, using inexpensive slide switches to control
a 12-volt auto radio, using the auto horn for the alarm. Comments will be provided
in the instructions for a different number of switches, different switch types, or
different alarm devices.
Let us say you decide to designate the "starting positions" as shown in Figure 2;
that is, switches A, B, D, and E UP. Further,
let us say you decide that the correct operating sequence (starting as in
Figure 2) will be: B, D, C, A, E. If the switches
are operated in this sequence, starting in the positions shown, operating voltage
will be supplied to the radio. However, if any switch is operated out of this
sequence, the horn will sound. Once the horn sounds, it will not be possible
to turn it off simply by reversing the switch (or switches) that caused it to
sound; that is, it will be latched. In order to reset (turn off the alarm),
all 5 switches must first be returned to the "starting positions," then
Switch B (the first one in the starting sequence) must be operated,
which will then reset the alarm.
In order to remove power from the radio, once it has been turned on as described
above, the switches must be operated in the exact reverse sequence to avoid
sounding the alarm. At any time that the alarm sounds, all 5 switches must be reset
to their "starting positions," then Switch B must be operated, which will
turn off the alarm.
Your selection of switch starting positions (UP or DOWN) and the physical mounting
sequences is very wide. For 4 switches, there are 24 possible permutations
of sequence and 16 possible UP/DOWN combinations for each, or 24 x 16 = 288
possible combinations in all. For 5 switches, the numbers rise to 120 x 32
= 3,840, for 6 switches, 720 x 64 = 46,080. The permutations
also give the mathematical odds against anyone's throwing the switches in the
correct sequence in one "blind" try.