MINDANAO UNIVERSITY OF SCIENCE AND TECHNOLOGY

College of Engineering and Architecture

DOOR KNOB ALARM

In Partial Fulfillment as a Requirement for ECE 21 (Electronics II)

Submitted By:

JOHANN JUDE G. ALBIA

JOJO I. EROJO

Submitted To:

LLOYD JHON B. ESTAMPA, MSEcE

February 2011

I. PROJECT BACKGROUND AND DESCRIPTION

In the year 2009 crime rate about robbery with homicide had increase. The PNP said that the

total crime volume in 2009 was recorded at 101,798 incidents with 61.26 % of these index crimes like robbery,

murder and other offenses against persons, and 38.74 % non-index offenses, or crimes against property. The PNP

said that crime rate in 2009 indicated a 63.79% increase, as the total crime volume in 2008 was only 62,148. In

line with this we as a students aim to help society through awareness of security precautions. For this we

have come up to introduce doorknob alarm.

The first documented invention of the doorknob appears in U.S. patent entries for the year 1878

when a patent for improvements on a door-closing device and Osbourn Dorsey invented it. Doorknobs

have been used around the world for centuries, and were first manufactured in the United States in the

mid nineteenth century. Doorknobs have been made of many materials including wood, glass, ceramic,

plastic and different types of metal. Brass is one of the most popular materials because of its excellent in

resistance to rust. The average doorknob is 2.25m in diameter. The basic components of doorknob are

the knob rose, shank, spindle, and knob-top. (See figure 1.1).

Figure 1.1 Basic components of doorknob

The door is an integral part of any door handle system. As far as main entry security goes the

doors role is to keep out undesirable. For interior doors, the door handle acts as a latch to keep the door

closed for privacy. Doorknob locks are an important part of any home security system. It is also true that

human by nature needs to protect themselves and this is the main objective of creating this research.

Doorknob Alarm does not just a closing device it is also helps home owner if the lock has broken. This

prevents a thief from being able to open the door by breaking the knob because of its alarming noise.

Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms. A

metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood

door. Anyone grabbing the knob from the outside is detected by the electrical capacitance change that

occurs from the human hand contact between the knob and the box. Almost all of the commercial

devices sold use a more expensive and power consuming radio frequency circuit approach to detect the

capacitance change. But, a very inexpensive and micro power technique can also work. This electronic

circuit schematic should dramatically reduce the cost of the device and the power drain is so small that it

will operate for many years from one set of AA or AAA batteries.

This doorknob security alarm turns an ordinary doorknob into a burglar alarm. Any thief will

first try your doors to see if they are unlocked. If a burglar touches your outside doorknob (must be a

wooden or fiberglass door -- will not work on metal doors) this device will instantly emit a loud alarm to

scare him away and alert you to the attempted entry. Unlike other alarms, the burglar will be stopped

before he enters your home or hotel room or office. Even if he is wearing gloves, the alarm will sound as

soon as the outside doorknob is touched.

This circuit emits a beep when someone touches the door-handle from the outside. The alarm

will sound until the circuit will be switched-off. The entire circuit is enclosed in a small plastic or

wooden box and should be hanged-up to the door-knob by means of a thick wire hook protruding from

the top of the case. A wide-range sensitivity control allows the use of the Door Alarm over a wide

variety of door types, handles and locks. The device has proven reliable even when part of the lock

comes in contact with the wall (bricks, stones, reinforced concrete), but does not work with all-metal

doors.

Let this paper be a trigger to all prospect readers to be conscious of two things: Safe and Secure.

II. TRANSISTORS UTILIZED IN THE PROJECT

A transistor is a semiconductor device used to amplify and switch electronic signals. It is made

of a solid piece of semiconductor material, with at least three terminals for connection to an external

circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing

through another pair of terminals. Because the controlled (output) power can be much more than the

controlling (input) power, the transistor provides amplification of a signal. Today, some transistors are

packaged individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is everywhere

in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the

field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers,

amongst other things.

The transistor used in this project is ZVNL110A MOSFET transistor. But this transistor is not

available in our city, so we will use a BS170 (See figure 2.1) transistor which is a good substitute to

ZVNL110A.

Figure 2.1 BS 170 Transistor

This BS170 is an N-channel, enhancement-mode MOSFET used for small-signal switching

applications. Packaged in a TO92 enclosure, the BS170 is a Vds<60 V (Vgs<20V) device capable of

switching in the 200-500 mA range with a minimum on-resistance of 1.2 Ω. The BS170 is nearly

identical to the 2N7000 (see figure 2.2), except that the leads are arranged differently.

Since it is also identical with 2N7000 (See figure 2.2), we will just use either of them yet for

sure; they both work perfectly on the project.

Figure 2.2 2N7000 Transistor

The 2N7000 is an N-channel, enhancement-mode MOSFET used for small-signal switching

applications. Packaged in a TO92 enclosure, the 2N7000 is a 60 V device capable of switching in the

200-350 mA range with an on-resistance of 0.3-5 Ω. The 2N7000 is nearly identical to the BS170,

except that the leads are arranged differently.

The main use of the 2N7000 is as a switch for low voltages and currents. In switching circuits, the

2N7000 can be used much like a bipolar junction transistor, but has some advantages:

low threshold voltage means no gate bias required

high input impedance of the insulated gate means almost no gate current is required

consequently no current-limiting resistor is required in the gate input

The main disadvantages of the 2N7000 over a bipolar transistor in switching are the following:

susceptibility to cumulative damage from static discharge prior to installation

circuits with external gate exposure require a protection gate resistor or other static discharge

protection

Non-zero ohmic response when driven to saturation, as compared to a constant junction voltage

drop in a bipolar junction transistor

The circuit symbol for the 2N7000 generally does not show the internal diode formed by the

substrate connection source to drain.

III. CIRCUIT FLOW EXPLANATION

Figure 3.1 The schematic diagram

3 sections: An Oscillator, The Sensor, & The Alarm

Notes:

This project uses a flip-flop as you can see at the oscillator and sensor stages. It is a circuit that

has two stable states and can be used to store state information. The circuit can be made to change state

by signals applied to one or more control inputs and will have one or two outputs.

The flip-flop has four inputs. These are:

D - DATA input: It is connected either to a LOW voltage, logic 0, or to a HIGH voltage, logic 1.

CLK or CK - CLOCK input: It responds to sudden changes in voltage, but not to slow changes

or to steady logic levels. The CLOCK input of the 4013B D-type bistable is rising-edge

triggered, meaning that it responds only to a sudden change from LOW to HIGH.

S - SET input: The SET input is normally held LOW. When it is pulsed HIGH, the outputs of the

bistable are forced immediately to the SET state, , .

R - RESET input: The RESET input is normally held LOW. When it is pulsed HIGH, the

outputs of the bistable are forced immediately to the RESET state, ,

Q and Q-bar – are the reactance outputs.

The flip-flop used in the circuit is a 4013B Flip-flop:

General Description:

The 4013B flip-flop is a monolithic complementary MOS (CMOS) integrated circuit constructed

with N- and P-channel enhancement mode transistors. Each flip-flop has independent data, set, reset,

and clock inputs and “Q” and “Q” outputs. These devices can be used for shift register applications, and

by connecting “Q” output to the data input, for counter and toggle applications. The logic level present

at the “D” input is transferred to the Q output during the positive-going transition of the clock pulse.

Setting or resetting is independent of the clock and is accomplished by a high level on the set or reset

line respectively.

Features:

Wide supply voltage range: 3.0V to 15V

High noise immunity: 0.45 VDD (typ.)

Low power TTL: fan out of 2 driving 74L

compatibility: or 1 driving 74LS

Applications

• Automotive • Data terminals • Instrumentation • Medical electronics • Alarm system

• Industrial electronics • Remote metering • Computers

To explain the circuit flow of this Project we will discuss each of its sections namely; the

oscillator, the sensor and the alarm.

The oscillator

The first section of the circuit is an oscillator based on a flip-flop. The flip-flop used in the

circuit is a 4013B flip-flop (see notes). CLK (node 3) and D (node5) are both grounded while R (node

4) is tied high. Hence, the output Q (node 1) will only be high if S (node 6) is high. When the output is

low, the transistor Q1 is cutoff. This allows S to be charged with a delay relating to the system of

impedances R1, R2, R3, and C3. Once the voltage at node 6 triggers S, the output changes to high and

Q1 is opened. Node 6 then discharges out through the capacitor. Once node 6 is low enough, S is no

longer triggered and the output is automatically reset (because R is tied high) to low and the process is

repeated.

Figure 3.2 shows node 6 charging and discharging as the blue trace. The yellow trace is the

output Q at node 1. You can see that the output turns high when node 6 reaches the switching threshold

of the flip-flop (about 1.8 volts). Right afterwards it spikes up due to feedback through C2, but quickly

starts discharging. The oscillator switches off when node 6 returns below the 1.8volt switching voltage.

Feedback through C2 draws node 6 to ground before the process repeats itself.

Figue 3.2

Source: http://photos.ruschmann.net/index.php?album=Electronics-Projects/Doorknob-Sensor&image=charge.png

Legend (traces):

---------- : Charging and discharging at S (node 6)

---------- : Output Q (node 1)

In order to change the period of oscillation, adjust the value at C3. If you would like to make the

pulses longer, adjust C2. The circuit works well right where it is at, though. Finally when Q1 opened the

next stage (the sensor) takes place.

The Sensor

The second section of the circuit is the sensor where the wire loop on the doorknob is involved.

This wire loop is one of the significant components of the project that is directly attached to the

doorknob. This will be the way that connects to the circuit if someone touches the doorknob outside.

After the oscillator section, the output at Q1 is divided down into two paths. First path is

connected in series with R4 (200 KΩ sensitivity potentiometer). This potentiometer can be adjusted to

lower or increase the output alarm as the circuit determines or detects that the doorknob is being

touched. The path to node 11 is the Clock input of the flip-flop, and the path to D (node 9) determines if

someone’s touches the doorknob or not.

Figure 3.3

Source: http://photos.ruschmann.net/index.php?album=Electronics-Projects/Doorknob-Sensor&image=touched.png

In figure 3.3, D (node 9) high than the clock. Hence, the flip-flop stays high when the leading

clock edge triggers it to lock. When the doorknob is touched, your body absorbs some of the charge and

D (node 9) charges slower. When the clock edge rises, D (node 9) is not high yet and low value is

locked into the flip-flop. Datas or informations from D (node 9) are now transferred to the output Q-bar.

The alarm

The last section of the circuit is the alarm; this is where we finally observe the final output which

is a sound alarm. We use an audible buzzer in order to relay the alarm. This is also my intent for the

circuit, but we use a LED in the photos because we cannot see sound. It is attached to the inverting

output of the second flip-flop Q-bar because it is high when the alarm is triggered.

The function of the alarm section is simple; it simply waits for the output Q-bar at the sensor

section to be delivered. It is only delivered if someone touches the doorknob and the alarm section will

now workout. Q2 is involved in the process. To end this circuit, the buzzer or LED (temporarily used) is

finally triggered to relay the alarm.

In addition, you can have a switch in order to turn the project on/off.

IV. PICTURES OF THE PROJECT

We don’t have actual photos yet on our project, we only have photos from the internet. The

circuit is temporarily and tested at the breadboard.

Fidure 4.1 Circuit layout using breadboard

source: http://photos.ruschmann.net/index.php?album=Electronics-Projects/Doorknob-Sensor&image=circuit.jpg

Figure 4.2 Circuit layout using breadboard

Source : http://photos.ruschmann.net/index.php?album=Electronics-Projects/Doorknob-Sensor&image=alarm3.jpg

In this photo, you could see on how the circuit is placed on the breadboard. A 3V DC voltage is

supplied by a AA cells battery. Resistors, capacitors, transistors, flip-flops, LED and wires are shown.

Figure 4.3 Installing the project

Source: http://photos.ruschmann.net/index.php?album=Electronics-Projects/Doorknob-Sensor&image=connected.jpg

The proper way of installing the project is shown in the figure 4.3. The wire is attached and

looped at the inside part of the doorknob. This wire would be sensitive and determines precisely if a

sudden movement or vibration is detected, when someone touches the doorknob outside.

V. BILL OF MATERIALS

QUANTITY MATERIAL COST

1 R1 4.7M Ω 1/4W resistor P0.35

1 R2 12K Ω 1/4W resistor P0.35

1 R3 2.2M Ω 1/4W resistor P0.35

1 R4 200K Ω (sensitivity adj.) potentiometer P8.50

1 R5 330K Ω 1/4W resistor P0.35

1 R6 470K Ω 1/4W resistor P0.35

1 R7 10K Ω 1/4W resistor P0.35

1 C1 47µ F P3.00

1 C2 0.0047 F P0.75

1 C3 0.022 µ F P0.75

1 C4 15p F P0.75

1 C5 12p F P0.75

1 C6 470p F P0.75

2 Q BS170 or 2N7000 P3.00

2 Flip-flop 4013B P28.00

2 AA Cells P15.00

1 Buzzer Star MMB-01 P45.00

1 PCB(3”x4”) P12

1 Battery Holder P10

1 box P30

TOTAL COST P160.35

VI. REFERENCES

http://www.discovercircuits.com/DJ-Circuits/dooralm2.htm

http://www.discovercircuits.com/H-Corner/doorknob.htm

http://www.datasheetcatalog.org/datasheet/zetexsemiconductors/zvnl110a.pdf

http://superpositioned.com/2006/04/25/doorknob-touch-alarm/

http://superpositioned.com/files/dooralm2.pdf

http://www.electronics-project-design.com/