Component Part List:

• C1 = 1uF 25V
• C2 = 220uF 25V
• R1 = 2.2K Ohm
• Q1 = 2N3904 / 2N2222
• D1 = 1N4148 / 1N4001-1N4007
• K1 = 12V SPDT Relay / Any appropriate relay with 12V coil
• U1 = LS7220 Digital Lock IC
• S1-S12 = SPST Momentary Pushbutton? Keypad (see notes)
• HD1 = 12 Position Header

Circuit Notes:

This could be the circuit diagram of a easy electronic combination lock by using IC LS 7220.This circuit may be applied to activate a relay for controlling (on & off) any device each time a preset combination of 4 digits are pressed.The circuit may be operated from 5V to 12V.

To set the mixture connect the appropriate switches to pin 3,4,5 and 6 of the IC through the header.As an example if S1 is connected to pin 3, S2 to pin 4 , S3 to pin 5, S4 to pin 6 of the IC ,the combination is going to be 1234.This way we can create any 4 digit combinations.Then connect the rest of the switches to pin 2 of IC.This will cause the IC to reset if any invalid key is pressed , and entire key code has to be re entered.

When the correct key combination is pressed, then the output ( relay) will be activated for a preset time driven by the capacitor C1.Here, it is set to be 6S.Increase the value of C1 to increase the preset time.

For the keypad, arrange the switches in a 3X4 matrix on a PCB (Printed Circuit Board).Write the digits on the keys by using a marker.Instead of applying numbers I wrote some symbols!.The bad guys is going to be more confused with this.

Download LS7220 datasheet from the following link:

LS7220 Datasheet - MOS digital lock circuit

1 file(s) 63.51 KB

Download Datasheet

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This is a car alarm simulator which using the LED as a simulation output. This simple circuit can tell you whether your car is running or not by detecting the voltage difference when the car is on and off. This occurs because when your car is running the Alternator puts a out a voltage a little bit higher than when the car is off. This circuit comes with low current consumption of 12mA max and run with 12V only.

The circuit will be activated automatically when the engine is turned off.

How to run the circuit:

1. Connect the circuit to the car electrical system.
2. Adjust RV1 until the LED flashes when the engine is not running
3. Start the engine, the LED should turn off. If the LED still on, the andjust the RV1 slighty

This circuit actually is a kits, you can get the kits at http://www.electronickits.com/kit/complete/surv/vemk126.htm. But it is very possible to you to build your own car alarm simulator circuit.

Download the car alarm simulator circuit kit manual / instruction from below link:

Car Alarm Simulator Kit Manual

1 file(s) 179.73 KB

Download Kit Manual

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FIG.l – ONE OF THREE OUTPUTS goes low depending on whether loop resistance is too high, too low, or just right.

Figure 1 shows a circuit that does the job. It”s a somewhat unusual application of a National Semiconductor LM3915 IC, normally used to drive LED” bargraph displays. That chip happens to contain the right combination of comparators and logic circuits to do what you need.

Step 1 is to translate the loop resistance into a voltage; that”s done by putting it into a voltage divider with resistors R1 and R2. Capacitor C2 protects the circuit against electromagnetic noise-important because burglar alarms use long wires, often running near heavy electrical equipment.

Step 2 is to translate the voltage into a logic signal indicating whether it”s in resisthe correct range. That”s where the LM3915 comes in. Normally, the LM3 9 15 would drive ten LEDs, one for each of ten small ranges of voltage. To obtain logic-level outputs, we have it driving 1K resistors instead of LEDs. Since we only need to distinguish three situations, not ten, we tie some of the outputs together. The LM3915 has open-collector outputs that can be paralleled in that way.

FIG.2 – THIS TRUTH TABLE shows the states of outputs A, B, and C under different loop-resistance conditions.

The truth table in Fig. 2 shows how the outputs work. Note that they use negative logic (OV for “yes”, +5V for “no”), the opposite of ordinary logic circuits. You can use inverters such as the 74HC04 to produce positive logic signals if that”s what you need.

Finally, note that the circuit will actually work with any supply voltage from 3 to 25 volts. Of course, if the supply isn”t 5 volts, the outputs will not be compatible with j-volt logic circuits.

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Here is the circuit diagram of simple multitone alarm. This is a low cost circuit which is simple and easy to build. The main components of this circuit is based on dual op-amp MC1458 and LM 380. The two op amps inside the MC 1458 are used to produce square and triangular waves. LM 380 is used to amplify the output. The first op amp IC1a is wired as an astable multi vibrator and second op amp IC1b is wired as an integrator, to make the square wave triangle.

The two output square ans sine can be selected using switch S1 to the input of IC2 which amplifies it to drive the speaker. POT R4 can be used for tone adjustment.

Simple Multitone Alarm Notes

• IC1a and IC1b are same. So their power supply is common. Pin 6 of IC2 (inv input) has no connection.
• C1 and C2 are ceramic, C3 is electrolytic capacitor.
• A dual polarity power supply is needed here. Just need center tap transformer, bridge diode and an electrolytic capacitor. You may search the circuit in this site.

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Here is the DIY electronic cardlock security system that can be used as a lock to turn on dan turn off important electronic/electrical appliances. When card is inserted, depending upon the position of punched hole on the card, a particular appliance would be switched on. The card should be rectangular in shape with only one punched hole on it. Unused/broken card (ie expired credit card, student card etc) can be used for this circuit.

How The Cardlock Security System Works

The electronic cardlock security system circuit uses eight photo-transistors (T1 through T8) to sense the light. When there is no card in the lock, light from incandescent lamp L1 (40-watt, 230V) falls on all the photo- transistor detectors. Transistor T8 is used as enable detector for IC1 (74LS244). When light is incident on it, it conducts and its collector voltage goes low. This makes transistor T16 to cut-off, and its collector voltage goes high. This logic high on its collector terminal will inhibit IC1 as long as light is present on phototransistor T8.

IC1 will get enabled only when the card is completely inserted inside the lock mechanism. This arrangement ensures that only the selected appliance is switched on and prevents false operation of the system.

You can make these cards using a black, opaque plastic sheet. A small rectangular notch is made on this card to indicate proper direction for insertion of the card. If an attempt is made to insert the card wrongly, it will not go completely inside the mechanism and the system will not be enabled.

When card for any appliance (say appliance 1) is completely inserted in the mechanism, the light will fall only on photo-transistor T1. So only T1 will be on and other photo-transistors will be in off state. When transistor T1 is on, its collector voltage falls, making transistor T9 to cut-off. As a result, collector voltage of transistor T9 as also pin 2 of IC1 go logic high. This causes pin 18 (output Q1) also to go high, switching LED1 on. Simultaneously, output Q1 is connected to pin 1 of IC2 (ULN2003) for driving the relay corresponding to appliance 1. Similarly, if card for appliance 2 is inserted, only output pin 16 (Q2) of IC1 will go highmaking LED2 on while at the same time energising relay for appliance 2 via ULN2003. The same is true for other cases/appliances also.

The time during which card is present inside the mechanism, the system generates musical tone. This is achieved with the help of diodes D1 through D7 which provide a wired-OR connection at their common-cathode junction. When any of the outputs of IC1 is logic high, the commoncathode junction of diodes D1 through D7 also goes logic high, enabling IC3 (UM66) to generate a musical tone.

In this electronic cardlock security system circuit IC1 (74LS244) is used as buffer with Schmitt trigger. All outputs (Q1 through Q7) of this IC are connected to IC2 (ULN2003) which is used as relay driver. IC2 consists of seven high current relay drivers having integral diodes. External free-wheeling diodes are therefore not required.

When an input of this IC is made logic high, the corresponding output will go logic low and relay connected to that pin gets energised. This switches on a specific appliance and the corresponding LED.

Once a specific card is inserted to switch on a specific relay, that relay gets latched through its second pair of contacts. Thus even when the card is removed, the specific appliance remains on. The same holds true for all other relays/appliances as well. The only way to deenergise a latched relay after removal of the corresponding card is to switch off the corresponding switch (S1 through S7) which would cut-off the supply to the desired relay.

The +5V and +12V supplies can be obtained with conventional arrangement using a step-down transformer followed by rectifier, filter and regulator (using 7805 and 7812 etc), you may find the circuit design on power supply category.

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This is the circuit diagram of car audio system anti theft security which can be effectively used to protect and secure your expensive car audio system from stealing. This simple circuit designed based on popular CMOS NAND chip CD4093,.

When the circuit is switched on via switch S1, the indicator LED1 will glow and the circuit state will be in the standby mode. LED inside optocoupler IC1 is lit as the cathode terminal is connected through the car audio (amplifier) body. As a result, the output at pin 3 of gate N1 goes low and disables the rest of the circuit.

Whenever an attempt is made to remove the car audio from its mounting by cutting its connecting wires, the optocoupler immediately turns off, as its LED cathode terminal is hanging. As a result, the oscillator circuit built around gates N2 and N3 is activated and it manages the “on” / “off” timings of the relay via transistor T2. (Relay contacts can be used to energize an emergency beeper, indicator, car horns, etc, if desired.)

Change the values of capacitor C2 to get different “on” / “off” timings for relay RL1 to be “On” / “Off”. With 100uF we get about 5 seconds as “on” and 5 seconds as “off” time. You may make your own experiments as needed.

Gate N4, with its associated components, forms a self-testing circuit. Normally, both of its inputs are in “high” state. However, when one switches off the ignition key, the supply to the car audio is also disconnected. Thus the output of gate N4 jumps to a “high” state and it provides a differentiated short pulse to forward bias transistor T1 for a short duration. (The combination of capacitor C1 and resistor R5 serves as the differentiating circuit.)

As a result, the buzzer in the collector terminal of T1 beeps to announce for a short duration that the safety circuit is intact. This period of “on” ring can be varied by changing the values ??of the capacitor C1 and / or resistor R5.

After construction, fix the LED and buzzer in dashboard as per your requirement and hide switch S1 in a in a convenient place. Then connect lead A to the body of car stereo (not to the body of vehicle) and lead B to its positive lead terminal. Take power supply for the circuit from the car battery directly.

Warning: This design is meant for car audios with negative ground only.

The post Car Audio System Anti Theft Security appeared first on Circuit Schematic Diagram.

The supply power for this door touch alarm is 3V DC, two AA batteries can be used to operate this circuit to make this circuit portable. Since this circuit consumes very small power, the battery will be last very long. A variable resistor used to adjust the sensitivity of the touch.

Please read above schematic diagram and some notes on the image diagram first before assemble this circuit.

Download the schematic drawing

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This laptop / notebook protector is powered by a 12V miniature battery used in remote control devices. IC TLO71 (IC1) is used as a voltage comparator with a potential divider comprising R2 and R3 providing half supply voltage at the non-inverting input (pin 3) of IC1. The inverting input receives a higher voltage through a water-activated tilt switch only when the probes in the tilt switch make contact with water.

When someone tries to take the laptop case, the unit takes the vertical position and the tilt switch breaks the electrical contact between the probes Immediately the output of IC1 becomes high and monostable IC2 is triggered. The low output from IC2 triggers the pnp transistor (T1) and the buzzer starts beeping. Construct the circuit as compactly as possible so as to make the unit matchbox size.

Make the tilt switch using a small (2.5cm long and 1cm wide) plastic bottle with two stainless pins as contacts. Fill two-third of the bottle with water such that the contacts never make electrical path when the tilt switch is in vertical position. Make the bottle leak-proof with adhesive or wax. Fix the tilt switch inside the enclosure of the circuit in horizontal position.

Fit the unit inside the laptop case in horizontal position using adhesive. Use a miniature buzzer and a micro switch (S1) to make the?compact gadget with this circuit. Maintain the laptop case in horizontal position and switch on the unit. Your laptop / notebookis now protected from stealing.

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This is the circuit diagram of car anti-theft to protect and increase the security of your car, prevent your from stealing. This circuit is very simple, low cost and easy to built. When key-operated switch S2 of the car is turned on, 12V DC supply from the car battery is extended to the entire circuit through polarity-guard diode D5. Blinking LED1 flashes to indicate that the car protection circuit is enabled. It works off 12V power supply along with current-limiting resistor R4 in series.

When the car door is closed, door switch S1 is in “on” condition and 12V power supply is available across resistor R1. This condition will? prevent transistor T1 from conducting. In this position, anti-theft protection circuit is in sleep mode.

When someone opens the car door, switch S1 becomes “off” as shown in Image #2. As a result, transistor T1 conducts to fire relay-driver SCR1 (BT169) after a short delay introduced by capacitor C1. Electromagnetic relay RL1 energises and its N/O contact connects the power supply to piezobuzzer PZ1, which starts beeping to indicate that someone is make a try to steal your car. To reset the circuit, turn off switch S2 using car key. This will cutoff the power supply to the circuit, so the buzzer sound will be stopped.

Collect the circuit on an universal PCB and house in a little box suit to your car. Connect the switch S1 to th ecar door and keep piezobuzzer Pz1 at a suitable place in your car.

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This is the circuit diagram electronic door lock security key system. It means that this security system circuit is the combination of pressed key itself (not the mechanical). The output can be connected to drive the relay to open the door (usually using motor).

It is a quite simple circuit of electronic door lock with security code of 7 digits. Attention must be paid in time we pressed the keys forming the code and there is no delay. With the right keys and if the correct code will activate the output Q7 for about 4 seconds, driving the transistor Q2, which can be used to activate a relay and opening the door, or can be used for any other circuit. The LED used for visual indication of activation. The seven-digit combination code of the above circuit is: 1704570, but can be changed the combination of secure key by exchange the connections between the outputs of the counter IC1 and switches.

Electronic Door Lock Security Key Components List

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