Circuit electrinic

The circuit diagram of a simple electronic code lock is shown in figure. A 9-digit code number is used to operate the code lock.When power supply to the circuit is turned on, a positive pulse is applied to the RESET pin (pin 15) through capacitor C1. Thus, the first output terminal Q1 (pin 3) of the decade counter IC (CD 4017) will be high and all other outputs (Q2 to Q10) will be low. To shift the high state from Q1 to Q2, a positive pulse must be applied at the clock input terminal (pin 14) of IC1. This is possible only by pressing the push-to-on switch S1 momentarily.

Circuit diagram:

Simple Electronic Code Lock Circuit Diagram

On pressing switch S1, the high state shifts from Q1 to Q2. Now, to change the high state from Q2 to Q3, apply another positive pulse at pin 14, which is possible only by pressing switch S2. Similarly, the high state can be shifted up to the tenth output (Q10) by pressing the switches S1 through S9 sequentially in that order. When Q10 (pin 11) is high, transistor T1 conducts and energises relay RL1. The relay can be used to switch ‘on’ power to any electrical appliance. Diodes D1 through D9 are provided to prevent damage/malfunctioning of the IC when two switches corresponding to ‘high’ and ‘low’ output terminals are pressed simultaneously.

Capacitor C2 and resistor R3 are provided to prevent noise during switching action. witch S10 is used to reset the circuit manually. Switches S1 to S10 can be mounted on a keyboard panel, and any number or letter can be used to mark them. Switch S10 is also placed together with other switches so that any stranger trying to operate the lock frequently presses the switch S10, thereby resetting the circuit many times. Thus, he is never able to turn the relay ‘on’. If necessary, two or three switches can be connected in parallel with S10 and placed on the key-board panel for more safety. A 12V power supply is used for the circuit. The circuit is very simple and can be easily assembled on a general-purpose PCB. The code number can be easily changed by changing the connections to switches (S1 to S9).

There are not many AM transmitters that are easier to build than this one because the inductor is not tapped and has a single winding. There is no need to wind the inductor as it is a readily available RF choke (eg, Jaycar Cat LF-1536). To make the circuit as small as possible, the conventional tuning capacitor has been dispensed with and fixed 220pF capacitors used instead. To tune it to a particular frequency, reduce one or both of the 220pF capacitors to raise the frequency or add capacitance in parallel to lower the frequency. Q1 is biased with a 1MO resistor to give a high input impedance and this allows the use of a crystal ear piece as a low cost microphone. 

Author: Peter Goodwin
Source http://www.extremecircuits.net/2010/05/simple-am-transmitter.html

The tuned circuit so formed is buffered by JFET Q2 and transistor Q3 which form a cascode stage with about 3dB of gain. The JFET provides a high impedance so that the loading of the tuned circuit is minimal (note: an MPF102 can be substituted if you cannot obtain a 2N5485). The RF output from Q2s collector can be monitored by an oscilloscope to easily find the point of resonance and read the frequency. Alternatively, the RF output can be read by an external frequency meter. Diodes D1 & D2 and the 5.6nF capacitors form a voltage doubler rectifier to drive a 100µA DC meter so that the resonance can be found (in the absence of an oscilloscope).


Trimpot VR1 provides a sensitivity adjustment for the meter. Transformer T1 is wound on a 12mm diameter ferrite toroid core. The primary winding consists of 50 turns of 0.2mm diameter enamelled copper wire, while the secondary is a single turn consisting of a strip of brass 0.5mm thick and 2.5mm wide bent into a horseshoe shape and threaded through the centre of the toroid. VC is a small AM tuning capacitor with both gangs connected in parallel.

To measure Q, the output of the RF signal generator should be around 0.5V peak. Adjust the frequency until the meters reading peaks, then adjust VR1 so that the meter reads full scale (100µA). Read the resonance frequency F0 from the frequency scale of the signal generator or better still, the reading on a frequency meter.

Next, increase the signal frequency until the meter reads 70µA and note this frequency as F2. That done, reduce the frequency on the signal generator below the resonance frequency until the meter again reads 70µA and note this frequency as F1. The Q can now be calculated as:

Q = F0/(F2 - F1)

While using a variable tuning capacitor will enable a wider range of inductors to be tested, the main advantage is estimating the distributed capacitance of the inductor as well. To do this, you have to calibrate the tuning scale with a capacitance meter, by measuring the capacitance across the tuning capacitor with no inductor connected. This is done with the unit switched off. Marking off increments of 20pF should be sufficient.

Set the tuning capacitor to say ¼ of its maximum value and note this value as C1. Adjust the RF signal generator frequency so that the inductor under test is at resonance and note this frequency as F0. Now set the RF generator frequency to half F0, adjust the tuning capacitor until resonance and note this capacitance as C2. The distributed capacitance of the inductor is (C2 - 4C1)/3.

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                 Circuit displaying a cell phone jammer.Here i have used a fm transistor for making this circuit.Mobile cellphones are working in 450  MHz  frequency .Here the transmitter generate virtually equal to 450 MHz  frequency there for the mobile telephone does not determine the original signal however the sign range may be very week so this circuit working in most effective 100 m range .This circuit working in handiest 450 Mhz .Do now not supply extra than three V



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vehicle immobilisers are fitted as standard to modern cars and heavy goods vehicles. Anti-theft mechanisms have become more sophisticated but so have the methods employed by crooks. Nowadays once the thief has gained access to a vehicle they will most likely use an electronic deactivation tool which seeks to disable the immobiliser, once this has been accomplished a blank transponder key/card can be used to start the engine. In many cases communication with the immobiliser is made using the OBD-II diagnostic connector.

Although the OBD-II protocol itself does not support the immobiliser, the vehicle manufacturer is free to use the interface as neces-sary for communication, either the standard OBD-II signals or unused pins in the OBD-II connector (i.e. those undefined in the OBD-II standard). Using one of these pathways the immobiliser can usually be electronically disabled. 

This may be unsettling news for owners of expensive vehicles but when professional car-thieves call, armed with the latest OBD-II hacking equipment this simple low-cost low-tech solution may be all that you need. The idea is ver y simple: if all connections to the OBD-II connector are disconnected there is no possibility for any equipment, no matter how sophisticated to gain access via the vehicle’s wiring. 

The OBD-II connector is usually locate d underneath the dashboard on the passenger side; once its wiring loom has been identified a switch can be inserted in line with the wires. The switch should be hidden away some-where that is not obvious. In normal opera-tion you will be protected if the vehicle is run with the wires to the socket disconnected. Make sure however that you throw the switch reconnecting the socket before you next take the vehicle along to a garage for servicing or fault diagnosis. 

The diagram shows the ISO K and ISO L wires switched. To cover all bases it is wise for every wire to the socket is made switchable except the two earth connections on pins 4 and 5 and the supply voltage on pin 16. Almost ever y vehicle manufacturer has their own method of vehicle immobilisation, by disconnecting every wire it ensures that no communication is possible (even over the CAN bus). Now the innermost workings of your vehicle will be safe from prying eyes. When a hacker plugs in a deactivation tool it will power up as normal but probably report something like ‘protocol unrecognised’ when any communication with the OBD port is attempted. 

Author : Florian Schäffer - Copyright: Elektor

The TDA7294 is a Hi-Fi amplifier and can give 100W RMS but with 10% distortion. Supplying 30 Volts you can have 50 Watts RMS with 1% distortion. Frequency range start at 16Hz and can reach 100KHz. Make sure you are using good heatsink. The chip supports mute function as well.