Douglas Krantz - Technical Writer - Describing How It Works
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How do You Use the Switches for Addressing?

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Hi Douglas,

Can you tell me how the switches work when addressing addressable fire alarm devices?

Thank you, R R

I'm assuming you are referring to the little switches used for addressing purposes on the detectors and modules.

For the fire alarm system, the numbers on the switches on the detectors and modules represent a number used in identification (addressing). This is similar to a phone number.

A cell phone communicates with the phone company, and uses a number to tell the phone company which phone is sending a signal. A fire alarm detector or module communicates with the control panel, and uses an address number to tell the control panel which detector or module is sending a signal.

All numbers, though, whether from a cell phone or a fire alarm detector/module, have to be sent as a binary series of ones and zeros. A cell phone does the conversion automatically, a fire alarm detector/module does this semi-automatically using thumbwheels or manually set binary switches.

I'll talk about the automatic thumbwheels first.

Thumbwheels - Decimal

Decimal thumbwheels show in plain numbers what address is being used in a fire alarm system
When thumbwheels are used for addressing, the decimal thumbwheels use the numbers 00 through 99. Each of the two wheels has the numerical position 0 through 9.

(It's obvious, but stay with me anyway.) In decimal, the numbers 0 through 9 mean:
    0 = 0
    1 = 1
    2 = 2
    3 = 3
    4 = 4
    5 = 5
    6 = 6
    7 = 7
    8 = 8
    9 = 9

(Be Patient, I'll get to it.) Decimal thumbwheels are easy for us as humans to understand; What-You-See-Is-What-You-Get (Wysiwig).

In detail, the numbers shown on the thumbwheels are being converted and sent to the control panel. To send the number 43 using decimal thumbwheels, one of the thumbwheels is set to 4 and the other is set to 3. The 4 represents 40 (4 times 10) and 3 represents 3 (3 times 1). When you add the number represented by the first thumbwheel (40) to the number represented by the second thumbwheel (3) you have the number 43.

The module or detector then converts this digital number 43 to the binary number 00101011.

Ya, it sounds simple, but I'm still getting to it.

Thumbwheels - Hexadecimal

Hexadecimal thumbwheels each show the numbers 0 through F, which is actually 0 through 15.
It's no longer quite so simple. When adding the letters A through F to the numbers 0 through 9 on the thumbwheels, we change from a Base 10 (Decimal) way of thinking to a Base 16 (Hexadecimal) way of thinking, which is a little more like what computers use.

Hexadecimal:
    0 = 0
    1 = 1
    2 = 2
    3 = 3
    4 = 4
    5 = 5
    6 = 6
    7 = 7
    8 = 8
    9 = 9
    A = 10
    B = 11
    C = 12
    D = 13
    E = 14
    F = 15

Many times, the numbers shown on the diagrams the panels you use will show the numbers as hexadecimal (0 through F) so you don't have to convert the hexadecimal numbers to the normal decimal numbers (0 through 9), but when getting right down to it, the conversions are part of the whole numbering scheme.

To get the true number of 43, the hexadecimal thumbwheels don't show 43. They show the number represented by the first thumbwheel added to the number represented by the second thumbwheel.

To send the true number 43, using hexadecimal thumbwheels, the first thumbwheel is set to 2 and the second thumbwheel is set to B. The 2 represents 32 (2 times 16) and the B represents 11 (B or 11 times 1). When you add the number represented by the first thumbwheel (32) to the number represented by the second thumbwheel (11) you have the number 43.

The module or detector then converts this digital number 2B to the binary number 00101011. Notice that this is the same binary number as came from the decimal 0 through 9 thumbwheels shown above.

DIP Switches - Binary

DIP Switches are the binary that can be sent over the 2 wires of the Signaling Line Circuit (SLC) and the binary used in computers.
The DIP (Dual In-line Package) Switches are a little simpler than the thumbwheels (and therefore more cumbersome). A switch has 2 positions (0 through 1) rather than 10 positions (0 through 9) or 16 positions (0 through F). The switches work in Binary; either they are off or they are on. Two-positions means Binary, and Binary is the type of signal sent over the two wires of the Signaling Line Circuit (SLC).

Again, though, the switch positions represent numbers.
    Switch 1 = 0 or 1 (1)
    Switch 2 = 0 or 2 (1 X 2)
    Switch 3 = 0 or 4 (2 X 2)
    Switch 4 = 0 or 8 (4 X 2)
    Switch 5 = 0 or 16 (8 X 2)
    Switch 6 = 0 or 32 (16 X 2)
    Switch 7 = 0 or 64 (32 X 2)
    Switch 8 = 0 or 128 (64 X 2)

To get the true number 43, you add the numbers represented by the switches:
    Switch-on #6 = 32
    Switch-on #4 = 8
    Switch-on #2 = 2
    Switch-on #1 = 1
    All other switches off

You add the numbers represented by the turned-on switches and get a true total of 43.

The module or detector then uses the number on the switch, which is (Switch 8 to Switch 1) 00101011.

Yes, I know. There isn't really a "True" number. In this case I'm calling numbers "True" when using numbers that we all have grown up using, which are the numbers 0 through 9: Base 10, or Decimal.

Douglas Krantz
Get help finding those Ground Faults - Buy the book "Make It Work - Hunting Ground Faults" by Douglas Krantz - Ground Fault Hunting becomes easier when you know what causes the ground fault and what is needed to "see" the ground fault.
Get help finding those Ground Faults - Buy the book "Make It Work - Hunting Ground Faults" by Douglas Krantz - Ground Fault Hunting becomes easier when you know what causes the ground fault and what is needed to "see" the ground fault.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

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