Door Guard Knob Alarm circuit

Door Guard Knob Alarm circuit.
This is Door Guard Knob Alarm circuit with touch system. When thief caught on the door handle, makes it sound an alarm once. Use the the detector capacitance within the body.This project is a small and economical. Ideal for travelers or those who want security.

How does it works
The circuit working as Figure 1 a 9V battery there are the regulator to reduce voltage down to 5V . Which consist of a transistor-Q1,R1 and ZD1 serves as provide to some circuit. In circuit include the frequency generator of three set. Firstly set have L1,C2,C3 and Q2, the signal is coupling with C4, then them are bypass a negative range go out with D1 so have only a positive signal range to bias Q3.
Figure 1 Door Guard Knob Alarm circuit.

We can adjust a sensitivity of project with changing resistance at collector lead of Q3 at resistors R4/1, R4/2. When Q3 works, pin 9 of IC1/1 which is inverter is connected to ground. The output pin 8 so is “1” then through divide the voltage with R11 and R7 into bias for transistor-Q4 voltage from pin 8 of IC1/1. And some voltage will through C7,R8,D2,R9,C6,IC1/2 and R10 to bias for transistor-Q2

At the same time in normal state,which yet no hand touch to a knob door (connected with a check point) The working of transistor Q2, Q3 and Q4 will as above, that are Q4 act as on-off switch. To control operation of frequency generator of set 2 and 3.
Which if Q4 works (switch on circuit) The frequency generator of set 2 and 3 will do not work. Thus so no sound single anything loundly to peizo-PZ1

Suppose Hands of thieves touching door knobs. Nature of the body as a capacitor connected parallel with L1 and C2, cause the first frequency generator section stop working down. So no any signal through C4 come to bias transistor-Q3,

At pin 9 of IC1/1 there state “1”, But at pin 8 changed state is “0” cause Q4 without bias (switch off circuit)
When Q4 do not works. The frequency generator of 2 section. Which consist of IC1/3, IC1/4,R13 and C8 will generate low frequency signal.
Which this signal will be bias to Q5. Therefore Q5 so work briefly. The transistor-Q5 will be controller working of This frequency is a resonance with Piezo-PZ1, Makes it sound an alarm intermittently.

How to build circuit.

Copper layout size as actual on Figure 2. Firstly, required the equipment to complete before. For L1 that use wire No. 30-32 on IF form coil about 20 turns(IF coil of FM radio).

The components list.
R1,R6________10K_____________= 2 pcs.
R2,R5,R8,R9____1M____________= 4 pcs.
R3__________5.6K____________= 1 pcs.
R4/1________330K____________= 1 pcs.
R4/2________1.8M____________= 1 pcs.
R7,R12,R16____100K___________= 3 pcs.
R10__________150K___________= 1 pcs.
R13__________620K__________ = 1 pcs.
R14__________1K_____________ = 1 pcs.
R15__________47K____________ = 1 pcs.

C1______33uF 16V___Electrolytic__1 pcs.
C3______10pF 50V____Ceramic_____1 pcs.
C4______330pF 50V___Ceramic_____1 pcs.
C5,C7,C8__0.1uF 50V___polyestor____3 pcs
C6______ 10uF 16V____Electrolytic__1 pcs.
C9______0.01uF 50V___Ceramic_____1 pcs.

D1-D4____1N4148 Diode___________4 pcs.
Q1,Q4,Q5,Q5__CS9013 Transistors___4 pcs.
Q2,Q3_______CS9018 ___”________2 pcs.
IC1_______CD4069__Inverter IC____1 pcs.
PZ1 piezo-No. KPE-133
L1 see text.
L2 see text.

For L2 use small output transformer by use only side 3 leg. But the real does not use the the middle leg.

The piezo is a KPE-133 model. Which is a three leg version. And there are resonance frequency of 3600 Hz. We can choose to use a different version of it. But must have leg of equal size, and resonance frequency is similar.

The switch-S1 is a 6 lead type (The 3-way rocker) Rocking up – middle – rocking down. The position “OFF” in the middle. The legs of the switch should be long enough. If soldering to the PCB, Lever broke through Panel must be fitted. But if you can not find a model with long leg, so hold S1 with the panel, then wiring to PCB board.

Figure 2 Single sided pcb layout.

Additional equipment required is a “bracelet”. Which are used as detector. To opt for a type conductors only. Hanging by This burglar project a touch with doorknobs.

When have component due amount. It assembly a device on the PCB. Started, the device short first, followed by the device higher up respectively. By see the components layout on PCB in Figure 3.

Figure 3 The components layout.

At detect point that Connected to one end of the bracelet. The rest of the bracelet left. Not be connected to the electrical pathway on Printed circuit boards.

For 9 volts battery in Prototype was attached to the Panel of the machine. Using plastic as their hold. The Printed circuit boards attached to the back of the box. The height of the Printed circuit boards of must box is too high.

The applications
When you go in room and Locking knob, Followed by pressing the latch bolt. But still not sure. The need for this project. Ensure that this time you can sleep comfortably.

Applications simply use the chain strap knob inside. Then move the switch-S1 to position “High” or Was changed to use the variable resistors instead. But must to be close to the circuit.
Some may be Notice that If the thief gloves. This machine is working properly.

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Hi, sir

I want to know how to make L1, L2 inductor
and how to connect them to circuit

please give me some advice.

thank you


Hi sir,
May I know what are the values of L1, and L2? They are not explicitly mentioned in the text. Hope to receive your response as soon as possible. This project has really caught my attention. Thanks.

Prashant Singh

Hello sir! my name is Prashant Singh. sir I want to make an alarm circuit that can ring “PLEASE WAIT” and another can ring “PLEASE DON’T WAIT”. Sir can you please tell me how can make this circuit for my project. If possible please send the circuit diagram of that in E-Mail ID

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