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U.S. Patent 4,125,833

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 station, etc.

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:

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 instructions).

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.

Figure 2

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.

Demo SeqSwitch #1

Shown here is a demo SeqSwitch using 5 "toggle" push buttons; that is, when a button is pressed once, it changes its connections and when it is pressed again, it returns to the previous connections. If the switches are operated in the correct sequence, a green light on the panel lights; if any switch is operated out of sequence, a loud alarm inside the box is activated.

It must be noted that using "toggle" push buttons for a SeqSwitch may not be a good idea, because such switches return to the same position each time they are pushed, making it very difficult to operate without sounding the alarm, since you cannot tell which position each switch is in. It is therefore difficult to reset once the alarm has been energized!

Inside Demo SeqSwitch #1

Inside the box, the backs of the switches can be seen, also the alarm buzzer, the relay and the 9-volt batteries. The tiny horizontal components at top center are diodes. (I can't remember right now why I put two into this one!)

Of course, the alarm device does not need to be in the same enclosure as the switches and relay. In fact, the only limiting factor in locating various components together is the amount of wiring between them.

Important! Do not use 110-volt a-c voltages for a SeqSwitch! If you limit your operations to 9- or 12-volt sources, you will not risk receiving an electrical shock, although it would be possible to generate some heat, if you shorted wires together. But using higher voltages is definitely not advised. This web site specifically warns you that we will not be responsible for any damage or injury caused by attempting to construct or operate a SeqSwitch.

Demo SeqSwitch #2

Here is a second demo SeqSwitch, this one using 6 slide switches. This version uses a red panel light instead of a buzzer to indicate an incorrect sequence.

As stated earlier, various common kinds of DPDT switches can be used, with the above warning that "toggle" push buttons make it very difficult to operate properly AND to cancel the alarm when it has been energized.

Inside Demo SeqSwitch #2

With the back enclosure removed, the optional plug-in "program" card is visible. By wiring several different connection patterns on different cards, the same SeqSwitch could be used with different combinations.

There are no electrical components on the card. Its purpose is merely to interconnect the other components in different combinations without rewiring the switches themselves.

With the plug-in 'programming' card removed

In the third photo, a better view of the switch wiring can be seen with the card removed. The wiring of this 6-switch SeqSwitch is clearly more complex than that of the previous 5-switch version.

Now, are you interested in building your own SeqSwitch?

Follow this link to a Theory of Operation page, Construction Tips and a Parts List: