Security Circuits

People are requesting walkie-talkie and RF remote control schematics, so here are some. Building these circuits needs special equipment and expertise in RF circuits. If you have no experience in RF, I suggest that you choose the easy way and buy a ready-made RF module. Otherwise you can realize you have an exact copy of a circuit in your hand, still it doesn't work the way it should. 100s of RF circuits for every hobbyist, technician, student, and design professional. An nice reference tool which includes lots of rf circuits. look at these circuit ideas, some of them may need some modification if they are to work as advertised. Ideas along with pretty good descriptions for each circuit.

Siren	Alarm Circuits	Safety Circuits
Bug	Surveillance	Lock Circuits

Burglar Alarm With Timed Shutoff

When SI (sensor) is closed, power is applied to U2, a dual timer. After a time determined by C2, CI is ene..

Overvoltage Protection Circuit Circuit

When testing a circuit, a source of voltage that is variable and has overvoltage shutdown is veiy useful. In this circuit, Rl is adjusted to 1 to 2 V below the eventual shutdown threshold. R2 sets the trip voltage. When this voltage is reached, the circuit shuts the voltage to the circuit under test down...

Freezer meltdown alarm

The meltdown is a magnet held to a small stand by ice. A reed switch is below the magnet..

Siren Alarm Circuit

The ramp voltage from the low frequency oscillator 1C1 modulates IC2 thereby producing a rising and falling tone like the siren ..

Keyless Lock

The circuit uses a four-bit latch (Ul). What makes the circuit sequential is that the set input of the first bit latch is tied..

Series Parallel Loop Alarm Circuit

Two SCRs are used with two sensor loops. One loop uses series switches, the other loop parallel switches. When a switch actuation occurs, the SCR triggers...

1000Hz Pulsed Tone Alarm Circuit

IC1 generates a pulse that modulates the 1000-Hz tone generated by IC2...

Power failure detector

This circuit indicates that a power outage occured for 1, 10, 100, and 500 seconds with the values given for R* and C*..

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 after an intrusion. One CMOS CD4093B quad NAND gate, IC1, supplies both logic and analog timing functions with the aid of.....

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 current through relay Kl, which responds by closing its contacts and actuating whatever load is attached. After opening the lock,.....

Parallel Loop Alarm Circuit

Four parallel switches are used to monitor four positions. When a closure occurs on any switch, SCR1 triggers, which sounds the alarm...

Photo alarm

LDR1, a cadmium sulphide (CDS) photoresistive cell is used as the lower leg of a voltage divider between Vcc and ground. The timer terminals 2 and 6 are connected to the junction of the photocell and SENSITIVITY control Rl. The resistance of the photoresistive cell varies inversely as the light intensity; resistance is high when the illumination level is low; low in bright light. (The Radio Shack CDS cell 276-116 has a typically wide resistance rangeâ€”about 3 megohms.....

Wailing alarm

This circuit simulates the sound of an American police siren. IC2 is wired as a low frequency astable that has a cycling period of about 6 seconds. The slowly varying ramp waveform on Cl is fed to pnp emitter follower Ql, and is then used to frequency modulate alarm generator IC1 via R6. IC1 has a natural center frequency of about 800Hz...

Linear-ic-siren

A low-frequency, op-amp oscillator and a VCO, both configured from a single MC3405 ~dual op amp and dual comparator, are tbe major components in a siren circuit tbat can be made to produce various warbles and wails, or serve as an audio sweep generator. ..

The-wailing-siren

Transistors Ql and Q2, with feedback provided via Cl from the collector of Ql to the base of Q2, forms a voltage-controlled oscillator (VCO). De- pending on the voltage applied to Q2 "s base, the VCO frequency ranges from around 60 Hz to 7.5 kHz. The instantaneous voltage applied to the base of Q2 is determined by the values of C2, R2, R3, and R4. When pushbutton switch Sl is closed, C2 charges fairly rapidly to the maximum supply voltage through R2, a 22-KO fixed.....

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 front end has a two-stage wideband rf amplifier, and a forward-biased hot-carrier diode for a detector. ..

House Alarm Loop Circuit

This circuit offers open and closed loop contacts (switches 1,2,3) that triggers the alarm ON and stays ON for 5 -10 minutes. The trigering delay (entrance/exit) is 27 seconds. This simple alarm circuit Has also a cancel button for reseting the circuit to stand-by mode again......

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..

Siren Circuit

An LM380 audio IC is configured as a feedback audio oscillator. A transistor astable modulates this oscillator at a low frequency, ..

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 determined by R2 and R3, 1 100-kilohm linear potentiometer that varies the dc gain from 1 to 100, driving the 50 microampere.....

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Burglar Alarm - Circuit Easy - Electronics Projects

Electronics Project for Students and Hobbyist. Learn by Circuit Diagram.

Alarm Sensor Security Circuit Cookbook book - Blog de jeanieaoh

Alarm Sensor Security Circuit Cookbook book download Download Alarm Sensor Security Circuit Cookbook The Alarm, Sensor & Security Circuit Cookbook by Thomas Petruzzellis in Back Matter; Books on Re...

Security Alarm: Door Security Alarm Circuit

AND RESIDENTIAL SECURITY SYSTEMS instant-alarm circuit or by the N.C. or N.O. (Normally Open) delayed-alarm circuits. The activation period is adjustable from 30 sec. to 3 min. 5. Entry Delay : Det...

Electrinic and circuit: Security Alarm

Security Alarm. Thwart any attempt of burglary in your house using this alarm circuit. When someone opens the door of your room, it sounds an alarm intermittently and flashes light as well. The cir...

Toosell blog! | About Home Security Alarms

Nowadays, home security alarms use an electric circuit that is altered when the door or window is opened. The alarm will be triggered if the house owner's code is not entered into the system in eno...

Simple Luggage Security Alarm Schematic | Free Circuit Diagrams ...

The following schematic is really a very simple and easy build luggage security alarm circuit to alert you when a person tries to break the chain. Transistor T1 allows supply to the sound generator...

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