Everyday new circuits

1. House security system

Here is a low-cost, invisible laser

circuit to protect your house

from thieves or trespassers. A

laser pointer torch, which is easily available in the market, can be used to operate this device.

The block diagram of the unit shown

in Fig. 1 depicts the overall arrangement for providing security to a house.

A laser torch powered by 3V powersupply is used for generating a laser

beam. A combination of plain mirrors M1 through M6 is used to direct the

laser beam around the house to form a

net. The laser beam is directed to finally fall on an LDR that forms part of

the receiver unit as shown in Fig. 2.

Any interruption of the beam by a thief/

trespasser will result into energisation

of the alarm. The 3V power-supply circuit is a conventional full-wave rectifier-filter circuit. Any alarm unit that

operates on 230V AC can be connected

at the output.

The receiver

uni t   compr i ses

t w o   i d e n t i c a l step-down transformers (X1 and X2), two

6V relays  (RL1 and RL2), an LDR, a

transistor, and a few other passive components. When switches S1 and S2 are

activated, transformer X1, followed by a

full-wave rectifier and smoothing capacitor C1, drives relay RL1 through the

laser switch.

The laser beam should be aimed continuously on LDR.  As long as the laser

beam falls on LDR, transistor T1 remains forward biased and relay RL1 is

thus in de-energised condition. When a

person crosses the line of laser beam,

relay RL1 turns on and transformer X2 gets power supply and RL2

energises. In this condition,

the laser beam will have no

effect on LDR and the alarm

will continue to operate as long

as switch S2 is on.

When the torch is switched

on, the pointed laser beam is

reflected from a definite point/

place on the periphery of the

house. Making use of a set of

p r o p e r l y   o r i e n t e d   m i r r o r s

one can form an invisible net

of laser rays as shown in the

block diagram. The final ray

should  fall on LDR  of the

circuit.

Note. LDR should be kept

in a long pipe to protect it from

other   sour ces  of   l ight ,  and

i t s   t o t a l   d i s t a n c e   f r om  t h e

source may be kept limited to

500 metres.

                                   Here is the Diagram for it 

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2) Fastest finger first

Quiz-type game shows are increasingly becoming popular on television these days. In such games,

fastest finger first indicators (FFFIs) are

used to test the player’s reaction time. The

player’s designated number is displayed

with an audio alarm when the player

presses his entry button.

The circuit presented here determines as to which of the four contestants first pressed

the button and locks out the remaining three

entries. Simultaneously, an audio alarm and

the correct decimal number display of the corresponding contestant are activated.

When a contestant presses his switch,

the corresponding output of latch IC2

(7475) changes its logic state from 1 to 0. The combinational circuitry comprising

dual 4-input NAND gates of IC3 (7420)

locks out subsequent entries by producing the appropriate latch-disable signal.

Priority encoder IC4 (74147) encodes

the active-low input condition into the

corresponding binary coded decimal (BCD)

number output. The outputs of IC4 after

inversion by inverter gates inside hex inverter 74LS04 (IC5) are coupled to BCDto-7-segment decoder/display driver IC6

(7447). The output of IC6 drives commonanode 7-segment LED display (DIS.1,

FND507 or LT542).

The audio alarm generator comprises

clock oscillator IC7 (555), whose output

drives a loudspeaker. The oscillator frequency can be varied with the help of preset VR1. Logic 0 state at one of the outputs

of IC2 produces logic 1 input condition at

pin 4 of IC7, thereby enabling the audio

oscillator.

IC7 needs +12V DC supply for sufficient alarm level. The remaining circuit

operates on regulated +5V DC supply,

which is obtained using IC1 (7805).Once the organiser identifies the contestant who pressed the switch first, he

disables the audio alarm and at the same

time forces the digital display to ‘0’ by

pressing reset pushbutton S5.

With a slight modification, this

circuit can accommodate more than four

contestants.

                              Here is the circuit diagram for it

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3) Mobile detector

This handy, pocket-size mobile

transmission detector can sense

the presence of an activated

mobile phone from a distance of oneand-a-half metres. So it can be used to

prevent use of mobile phones in examination halls, confidential rooms,

etc. It is also useful for detecting the

use of mobile phone for spying and

unauthorised video transmission quired for a mobile bug.

Here the circuit uses a 0.22µF disk

capacitor (C3) to capture the RF signals

from the mobile phone. The lead length

of the capacitor is fixed as 18 mm with

a spacing of 8 mm between the leads to

get the desired frequency. The disk capacitor along with the leads acts as a

small gigahertz loop antenna to collect

the RF signals from the mobile phone

The circuit can detect both the incoming and outgoing calls, SMS and

video transmission even if the mobile

phone is kept in the silent mode. The

moment the bug detects RF transmission signal from an activated mobile

phone, it starts sounding a beep alarm

and the LED blinks. The alarm continues until the signal transmission ceases.

An ordinary RF detector using

tuned LC circuits is not suitable for

detecting signals in the GHz frequency

band used in mobile phones. The

t ransmi s s ion  f r equency of  mobi l e

phones ranges from 0.9 to 3 GHz with

a wavelength of 3.3 to 10 cm. So a circuit detecting gigahertz signals is reOp-amp IC CA3130 (IC1) is used

in the circuit as a current-to-voltage

converter with capacitor C3 connected

between its inverting and non-inverting inputs. It is a CMOS version using

gate-protected p-channel MOSFET

transistors in the input to provide very

high input impedance, very low input

current and very high speed of performance. The output CMOS transistor

is capable of swinging the output voltage to within 10 mV of either supply

voltage terminal.

Capacitor C3 in conjunction with

the lead inductance acts as a transmission line that intercepts the signals

from the mobile phone. This capacitor creates a field, stores energy and transfers the stored energy in the form of

minute current to the inputs of IC1.

This will upset the balanced input of

IC1 and convert the current into the

corresponding output voltage.

Capacitor C4 along with high-value

resistor R1 keeps the non-inverting input stable for easy swing of the output to high state. Resistor R2 provides

the discharge path for capacitor C4.

Feedback resistor R3 makes the inverting input high when the output becomes high. Capacitor C5 (47pF) is

connected across ‘strobe’ (pin 8) and

‘null’ inputs (pin 1) of IC1 for phase

compensation and gain control to

optimise the frequency response.

When the mobile phone signal is

detected by C3, the output of IC1 becomes high and low alternately according to the frequency of the signal

as indicated by LED1. This triggers

monostable timer IC2 through capacitor C7. Capacitor C6 maintains the

base bias of transistor T1 for fast

switching action. The low-value timing components R6 and C9 produce

very short time delay to avoid audio

nuisance.

Assemble the circuit on a generalpurpose PCB as compact as possible

and enclose in a small box like junk

mobile case. As mentioned earlier, capacitor C3 should have a lead length

of 18 mm with lead spacing of 8 mm.

Carefully solder the capacitor in standing position with equal spacing of the

leads. The response can be optimised

by trimming the lead length of C3 for

the desired frequency. You may use a

short telescopic type antenna.

Use the miniature 12V battery of a

remote control and a small buzzer to

make the gadget pocket-size. The unit

will give the warning indication if

someone uses mobile phone within a

radius of 1.5 metres. 

                  Here is the diagram for it

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4) Spy Bug

A FM transmitter Bug using 2 transistors and with a transmission range
of 800 meters !!

This FM transmitter Bug is very easy to build.
The size of the circuit board is ONLY 21mm x 15mm.


I design the circuit board layout using
Pain shop pro X2 ,it takes me 2 hours to get
the design right ,i want a very small PCB.

To make the PCB i will be using the toner transfer
method and Ferric Chloride.

Parts used:

1. Home made PCB ,21mm X 15mm
2. BC547 transistors x 2
3. 1nf ceramic capacitor
4. 10pf ceramic capacitor
5. 33pf ceramic capacitor
6. 22nf axial ceramic capacitor x 2
7. 1 - 5p to 30p air trimmer
8. 470R resistor
9. 10K resistor
10. 47K resistor
11. 68K resistor
12. 1M resistor
13. 10mm Mic
14. 175cm antenna
15. Battery Plug
16. Some solder
17. 9mm heatshrink

                                          Circuit Diagram

                                                               PCB diagram

                                                          Guide how to make

1. The size of the pcb should be 21mm x 15mm .
2. Tn this take out the diagram of spy bug  pcb design using printer.
3. Take a fibre glass copper coated board.
4. Iron the spy bug pcb design on the fibre glass coated copper board.
5. Applying the iron to the back of the spy bug pcb designed paper for 45 sec.
6. Next place the pcb in the water and peel black paper.
7. Now drill the pcb using drill machine drill bit size is 1mm.
8. Now cut the pcb to size.
9. The size of the pcb should be 21mm x 15mm.
10. Now dip it in ferric chloride for 9 min.
11. Now dip it in water.
12. Now use paint thinner to remove tonner.
13. Pcb all done.
14. Use FM radio to listen the spy bug.

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5) IR Remote Jammers

Parts Used 

1. R1-100K 1/4W Resistor
2. R2-150K 1/4W Resistor
3. R3-10K 1/4W Resistor
4. R4-1K 1/4W Resistor
5. R5-22 Ohm 1/4W Resistor
6. C1-10nF Ceramic Disc Capacitor
7. C2-1uF Electrolytic Capacitor
8. D1, D2, D3-High Output IR LED x3
9. Q1-2N4403 PNP Transistor
10. Q2-2N4401 NPN Transistor
11. S1-Normally Open Momentary Push Botton
12. B1-4.5V Battery (Three "AA"'s In Series)
13. MISC-Wire, Case, Board

How to make 

1. You may need to adjust the value of R3 for the right frequency. A pot can be used.
2. You may only need one IR LED.
3. It goes without saying that this circuit should be used with descretion.
4. The value of R5 depends on your supply voltage and LED. For a standard 4.5V supply and standard IR LED, use 22 Ohm as specified on the parts list. This forum topic covers this resistor as well as a few other issues with the circuit.

Circuit Diagram

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6) Electronic Dice

Parts Used

1. R1, R5, R6-22K 1/4W Resistor x3
2. R2-10K 1/4W Resistor
3. R3-4.7K 1/4W Resistor
4. R4-150K 1/4W Resistor
5. R7 - R13-330 Ohm 1/4W Resistor x7
6. C1-1uF Electrolytic Capacitor
7. C2-4.7uF Electrolytic Capacitor
8. D1-1N4148 Signal Diode
9. D2 - D8-Red/Green/Yellow LED x7
10. Q1-2N3904 NPN Transistor
11. U1-555 Timer IC
12. U2-74LS192 4 Bit Counter IC
13. U3-74LS08 Quad Intengreted AND Gate IC
14. S1-SPST Momentary Pushbutton Switch
15. MISC-Board, Wire, Sockets For ICs, Case

How to make

1. Pushing and holding S1 causes the LEDs to rapidly cycle. Releasing the button locks the pattern and shows a number from 1 to 6.
2. When building the circuit, make sure to position the LEDs as shown on the schematic. Otherwise the pattern of the dice will look weird.
3. Two circuits can of course be both powered by one switch to make a dual dice.

Circuit diagram

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