Security Circuits

Siren Circuits

Surveillance Bug Circuits

Alarm Circuits

Surveillance Circuits

Safety Circuits

Lock Circuits

FM Micro-Transmitter Bug Surveillance Circuit

The transmitter we recommend to build is quite simple. It can even be built by a beginner. However, unlike the ease of construction and its small size, it is almost certain that it will impress you with its outstanding performance. Its autonomy is 12-15 hours, with a 9 volt battery and its range is from 100 to 300 meters depending on the... .
Key Code Combination High Security Door Lock

This project is an electronic lock with many combinations that you can easily change and opens only with the correct combination of four consecutive numbers. The big advantage of the electronic lock is that the four numbers must be entered in the correct order one after the other. If a number is wrong then the circuit automatically resets to its... .
DBS-20-type leakage protection circuit

DBS-20-type leakage protection circuit .
HD a 3A limit energy-saving three-phase power protection circuit

Current Transformer H11-3 need be made. Choose not less than 2W transformer core, the first secondary winding. With µ0.12mm enameled wire around 1000 turns. Primary use µ1 ~ 4m .
Current leakage protection circuit

Current leakage protection is currently the most used and best leakage protection device. Current leakage protector fork into electromagnetic and electronic two, two leakage pr .
Rain alarm schematic circuit diagram

FIG. 1 is a circuit diagram of it, it is in the audio circuit from the resistance between the two leads to a probe to rain alarm. Fig. 2 with CCL to make a probe connected to t .
Fire Alarm schematic design

Explanation Here is a simple fire alarm circuit based on an LDR fire detection sensor. Smoke generated during circuit generates an audible alarm, fire smoke in case of fire. Al .
Structure and working principles of various protective circuit diagram e

Due to the different circumstances of the various input signals, when the pin is applied between the abnormal voltage, protection circuits to form a circuit path from while LSI .
Telephone electronic lock circuit

Electronic lock using the telephone key (resistor connected plug) is inserted after the oscillator circuit start-up circuit, and the oscillation frequency is accurate or not to .
Door alarm circuit with a time of recognition NE555

Door alarm here with a time recognition, the owner opened the door is normally open the door, open the door to complete the action within the general 30s, so it does not alarm, .
A resistor-capacitor circuit protection thyristor

Diode and thyristor can withstand over-current and over-voltage of poor, short-term over-voltage over-current will damage the components, but can not complete the full potentia .
Break burglar alarm circuit II

Ding for the circuit principle: care, vs SCR trigger grounded, it is in the off state. When someone leads A burglar broke, the SCR trigger end to give a trigger voltage is turn .
A third harmonic current phase protection circuits

Figure 4-27 (b) line than in Figure 4-27 (a) line more than a capacitor, to improve and increase the output current waveform DC voltage. Figure 4-27 (b) line shown can be used .
Amplifier input signal overdrive auto-protection

That circuit protects the overdriven signals going into an amplifier. Instead of a zener diode we use a transistor. That way we ensure that the above the ordinary input voltages ( 1 volt r.m.s.) can be acheaved without distortion. Also the use of a transistor limits the number of components used in this schematic.
Three-dial combination lock

Here's an effective little combination lock that you can put together in one evening's time. To open the lock, simply dial in the correct combination on the three rotary or thumbwheel switches. With the correct combination entered, current flows through Rl into Ql's gate terminal, causing the SCR to latch in a conductive state. This sends a... .
Warble-tone alarm

The circuit generates a warble-tone alarm signal that simulates the sound of a British police siren. IC1 is wired as an alarm generator and IC2 is wired as a 1 Hz astable multivibrator. The output of IC2 is used to frequency modulate IC1 via R5. .
Electronic combination lock

When button S12 (#) is pressed, a positive voltage fed through Rl appears at the base of transistor Ql, turning it on. When Ql is conducting, pin 1 of Ul is brought to ground 0ow) or the battery's negative terminal. With pin 1 low, two things occur: Pin 8 of Ul goes high ( + 9 volts dc), turning on LED 1â€”indicating that the circuit has been... .
Battery-powered fence charger

In essence, the circuit is nothing more than an auto ignition coil and a set of points which accomplishes the same thing. A pulsing circuit made from a single CMOS NOR integrated circuit (Ul), opens and closes the relay contacts to simulate the action of the original breaker points. The relay pulser is divided into two clocking functions. The... .
LF or HF field strength meter

CI and LI resonate on the 1750 meter band, with coverage from 150 kHz to 500 kHz. LI can be slug-tuned for 160-to-190 kHz coverage alone or a 2.5 mH choke can be used for LI, if desired, using CI for tuning. A 1N270 germanium diode rectifies the RF signal and C2 is charged at the peak RF level. This dc level is amplified by an LM358. The gain is... .
Overvoltage protection circuit

The silicon controlled rectifier (SCR) is rated to handle at least the current of the power supply. It is connected in parallel across the 12 V dc output lines, but remains inert until a voltage appears at the gate terminal. This triggering voltage is supplied by the zener diode. At potentials less than 14 V the zener will not conduct current.... .
Electronic ship siren

The circuit consists of a multivibrator (Ql & Q2), and a low power output stage Q3. The speaker should have an impedance in the region of 40 to 80 ohms. To use a low impedance speaker, connect an output transformer from the emitter of Q3 to ground. Cl and C2 determine the pitch of the siren and the values specified will provide a tone of about... .
Tarry light

The push button and potentiometer initiate a time delay that turns a light on then automatically turns it off again after a predetermined time. The potentiometer can be set for a delay of a few seconds to just under three minutes. When the push-button switch SW2 is pressed, capacitor Cl gets charged through D5 to the full dc voltage developed by... .
Ground tester

This circuit checks the reliability of appliances so that the equipment may be used safely. The test circuit must be plugged into a properly wired three terminal wall outlet. When a two-lead or three-lead appliance is plugged into circuit outlet SOI, neon lamps NE1 and NE2 will light if the appliance is safe .
Burglar-alarm

The single-chip, burglar -alarm circuit shown uses a dual 556 timer, draws 10 mA of standby current, and generates a pulsing alarm signal that conserves battery energy. Once activated, the alarm wilLremain on, independent of the subsequent state of any of the sensors. The sensors support both deferred and immediate-action modes. You can... .
Semiconductor-fail-alarm

False alarms produced by semiconductor failure are impossible with this burglar-alarm circuit equipped with relays. What"s more, the circuit is virtually immune to false triggering. With a standby current of less than 0.1 mA, the circuit offers all the features an alarm needs: entry and exit delays, a timed alarm period, and automatic reset... .
Burglar-alarm

The heart of the circuit is a 555 oscillator /timer, Ul, configured for monostable operation. The output of Ul at pin 3 is tied to the gate of SCRl. As long as Sl-S5, which are connected to the trigger input of Ul, are open, the circuit remains in the ready state, and does not trigger SCRl into conduction. Because the relay is not energized,... .
Closed-loop-tracer

The tracer, consisting of both a transmitter and receiver, is designed to follow a closed-loop wire or cable system. It follows an induced voltage path created by feeding a low-current, audio-frequency signal through the cable. When the pick-up coils come within close proximity of the current -carrying cable, a small voltage is generated... .
Bug-tracer

The bug tracer is made up of a simple rf-injector circuit consisting of Ql and Q2, and a pocketsize, AM broadcast receiver. The two-transistor rf-injector circuit supplies a constant rf signal to one end of a cable. Then the AM receiver is used as a detector, allowing you to trace the wire to its source. Transistor Ql, along with piezoelectric... .
Burst-power-control

Industrial applications sometimes require that power be only briefly applied to a load following the closure of a switch, such as a microswitch or foot switch. The load could be a heating element for use in sealing plastic bags, a de motor that is indexed or stepped with each application of power, or a de solenoid which is to be energized for... .
Flame-ignitor

The spark developed by the circuit is suitable for a gas ignitor. Capacitor Cl is charged through Rl and Dl toward peak line voltage. C2 is simultaneously being charged at a slower rate through R5. When the charge on C2 is sufficient.to trigger the PUT, the SCR is triggered on, providing a rapid discharge path for Cl through the transformer... .
Bug-detector

This rf detector can locate low-power transmitters (bugs) that are hidden from sight. It can sense the presence of a 1-mW transmitter at 20 feet. which is sensitive enough to detect the tiniest bug. As you bring the rf detector closer to the bug, more and more segments of its LED bar-graph display light, which aids in direction finding. The... .
Door-opener

The door opener derives its power from a 9-V battery. A momentary-contact switch, 52, is provided in the event that manual opening and closing is required. Relay Kl is a 9-V type and relay K2 is a 117"Vac latching-type, which automatically latches with the first burst of current and opens on the second burst. The gate lead of the LASCR is... .

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