This lightning detector circuit is a very sensitive static electricity detector that can provide an early warning of approaching storms from inter-cloud discharge well before an earth-to-sky return strike takes place. An aerial (antenna) formed of a short length of wire detects storms within a two mile radius.
The circuit emits an audible warning tone from a piezo buzzer, or flashes an LED for each discharge detected, giving you advance warning of impendig storms so that precautions may be observed.

Lightning detector schematic

The primary feature in the lighting detector is the circuit’s ability to be set close to self-oscillation, with its relaxation optimised via the bias resistor values shown in the circuit diagram. The oscillator is dc coupled and feedback is routed through the collector of TR1 to the base of TR2, while the overall loop gain is set with the multiturn(12, 18 or 22) preset VR1.

Lightning sensor setting up

To set up the lightning sensor, adjust preset VR1 for oscillation by monitoring test point TP1, which should be at roughly 7volts peak-to-peak. Test point TP2 should be at +6V dc. Now readjust VR1 back slightly to stop oscillation; use a screwdriver to touch the aerial-side of C1 several times; the alarm should sound for 1 or 2 seconds then stop. If it continues, make a very small adjustment back and recheck. The other method is to electrostatically charge a plastic ruler and then draw your finger close to discharge, about two meter away from the aerial.
Powered from a 9 volts battery the Lightning Detector circuit consumes about 600 uA in standby. Powered continously it could provide a good year of uninterrupted monitoring.
When sounding the alarm, the current will rise to 4mA depending on the low current sounder WD1. A minimum 3 volts device is required for a good output level and it will produce a “pinging” alarm to warn in real time of any electrostatic pulse activity.

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This luggage or bike alarm can be used while travelling by trains or bus and we generally lock our luggage using a chain-and-lock arrangement. But, still we are under tension, apprehending that somebody may cut the chain and steal our luggage. Here is a simple circuit to alarm you when somebody tries to cut the chain.

Luggage chain alarm diagram

T1 enables supply to the sound generator chip when the base current wire (thin enameled copper wire of 30 to SWG, used for winding transformers) loop arround the chain is broken by somebody, the base of T1, which was earlier tied to positive rail, gets opened. As a result, T1 gets forward biased to extend the positive supply to the alarm circuit. In idle mode, the power consumption of the circuit is minimum and thus it can be used for hundred of travel hours.
To enable generation of different alarm sounds, connection to pin 1 and 6 may be made as per the table bellow.

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This handy, pocket-size mobile transmission detector or sniffer can sense the presence of an activated mobile cellphone from a distance of one and-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.
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.

Mobile phone bug detector diagram

An ordinary RF detector using tuned LC circuits is not suitable for detecting signals in the GHz frequency band used in mobile phones. The transmission frequency of mobile phones ranges from 0.9 to 3 GHz with a wavelength of 3.3 to 10 cm. So a circuit detecting gigahertz signals is required for a mobile bug.
Here the circuit uses a 0.22?F 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.

Op-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 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 general purpose 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 meters.

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This simple code lock circuit described here is of an electronic combination lock for daily use. It responds only to the roght sequence of four digits that are keyed in remotely. If a wrong key is touched, it resets the lock. The lock code can be set by connectiong the line wires to the pads A, B, C and D in the figure. For example, if the code is 1756, connect line 1 to A, line 7 to B, line 5 to C, line 6 to D and rest of the lines-2,3,4,8 and 9 to the reset pad as shown by dotted lines in the schematic.

Code lock schematic

The code lock circuit is built around two CD4013 dual-D flip-flop ICs. The clock pins of the four flip-flops are connected to A, B, C and D pads. The correct code sequence for energisation of relay RL1 is realised by clocking points A, B, C and D in that order. The five remaining switches are connected to reset pad which resets all the flip-flops. Touching the key pad switch A/B/C/D briefly pulls the clock input pin high and the state of flip-flop is altered. The Q output pin of each flip-flop is wired to D input pin of the next flip-flop while D pin of the first flip-flop is grounded. Thus, if correct clocking sequence is followed then low level appears at Q2 output of IC2 which energises the relay through relay driver transistor T1. The reset keys are wired to set pins 6 to 8 of each IC. (Power-on-reset capacitor C1 has been added at EFY during testing as the state of Q output is indeterminate during switching on operation.)
This simple code lock circuit can be usefully employed in cars so that the car can start only when the correct code sequence is keyed in via the key pad. The code lock design can also be used in various othee application.

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Here is a very simple telephone broadcaster or transmitter which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier.
One important feature of this phone transmitter iss that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its performance. The phone bug transmitter is very tiny and can be built using a single -IC type veroboard that can be easily fitted inside a telephone connectin box of 3.75cm x 5cm.

Spy phone transmitter schematic

The spy phone transmitter consists of two sections, namely, automatic switching section and FM transmitter section.
Automatic switching section comprises resistors R1 to R3, preset VR1, transistor T1 and T2, zener D2 and diode D1. Resistor R1, along with preset VR1, works as a voltage divider. When voltage across the telephone lines is 48V DC, the voltage available at wiper of preset VR1 ranges from 0 to 32V (adjustable).
The switching voltage of the circuit depends on zener breakdown voltage and switching voltage of the transistor T1. Thus, if we adjust preset VR1 to get over 24.7 volts, it will cause the zener to breakdown and transistor T1 to conduc. As a result collector of transistor T1 will get pulled towards negative supply, to cut off transistor T2. At this stage, if you lift the handset of the telephone, the line voltage drops to about 11V and transistor T1 is cut off. As a result, T2 gets forward biased through R2 to provide a DC path for T3 used in the following FM transmitter section.
The low-power FM transmitter section comprises oscillator transistor T3, coil L1 and a few other components. T3 works as a common-emitter RF oscillator, with T2 serving as an electronic “on/off” switch. The audio signal available across the telephone lines automatically modulates oscillator frequency via T2 along with its biasing R3. The modulated RF signal is fed to the antenna. The telephne conversation can be heard on an FM receiver remotely when it is tuned to the transmitter frequency.

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A beautiful mobile phone jammer schematic diagram for use only in GSM1900 with frequency from 1930 MHz to 1990 MHz. The GSM1900 mobile phone network is used by USA, Canada and most of the countries in South America. This cell phone jammer is not applicable for use in Europe, Middle East, nor Asia.
The GSM jammer circuit could block mobile phone signals which works on GSM1900 band, also called DCS.

Mobile cell phone jammer schematic

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This is a very simple 9V low battery indicator circuit which has 2 LEDs, one green which will light up when the battery voltage is higher than 6.9 volts and one red LED which will light up when the battery voltage is bellow 6.9 volts. You can use BC547 … BC549 .

Low battery indicator schematic

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The MAX4467 is a micropower op amp optimized or use as microphone preamplifiers. They provide the ideal combination of an optimized gain bandwidth product vs. supply current, and low voltage operation in ultra-small packages. The MAX4465/ MAX4467/MAX4469 are unity-gain stable and deliver a 200kHz gain bandwidth from only 24µA of supply current.
Download MAX4467 datasheet

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