EngineeringSlash- The electronic projects,electronic project,electronic schematic,electronic design » Electrical engineering http://www.engineeringslash.com Engineering blog- electronic circuits , electronic projects,electronic schematic,electronic design,simple circuit and hobby circuits Tue, 09 Feb 2010 05:03:16 +0000 en hourly 1 http://wordpress.org/?v=3.3.1 Electronic Lock http://www.engineeringslash.com/digital-ic/electronic-lock.html http://www.engineeringslash.com/digital-ic/electronic-lock.html#comments Mon, 25 Jan 2010 10:43:30 +0000 admin http://www.engineeringslash.com/?p=188 Here is an electronic code lock, which can be used as a door latch or key for ignition, etc. Operation is fairly tricky and there lies the beauty of the circuit. There are a number of switches, actually nine, which should be operated in a particular and owner – configured -sequence, or else the circuit will not drive the final SCR. The switches can of course be reconfigured as desired. SCR Output should be used with a suitable driver such as a solenoid for the door latch or a relay for the key.

Electronic Lock circuit 300x162

The circuit is shown in Schematic 29. CD 4066 quad bilateral switch is made use of here. 12 V DC powers the circuit through SI. External switches S2—S9 are not connected in the same order as their number and that is part of the trick.

52 is a dummy switch, when pressed, LED D2 lights up only to fool the intruder. It is not connected to the rest of the circuit.

53 is the next switch. This operates internal switch 1 of CD 4066. When this switch is pushed, it pulls up trigger terminal (Pinl), and switch across 13 and 2 (SW1) is closed. It stays closed because of the feedback action of 3.3M resistance (Rl). Dl lights up indicating the closure of one switch in the sequence.

This powers the second internal switch (SW2) consisting of 5, 4, 3 pins. Power reaches Pin 5 and Pin 4 is the trigger terminal. When S5 switch is pushed on internal switch across 5 and 3 (SW2) closes. It charges CI capacitor 47uf through 100K resistance (R3). It can now feed the next switch as long as the capacitor can hold charge. CI is discharged through D3 and R5, which mean that next switch should be operated before this charge finishes.

To add to the confusion, the next switch is actually two switches in series comprising of S4 and S7 with trigger terminal at Pin 6. If they are pressed simultaneously, only if they are pressed simultaneously, internal switch across pins 8 and 9 (SW 3) closes. This charges 47uF capacitor (C2) through 100 k resistor (R6) which discharges through D4 and R7. Hence one has to press the next switch S8 before this charge is completed.

When S8 with trigger terminal at Pin 12 is operated in time, internal switch across pins 11 and 12 (SW4) closes.

SCR is fired now through R9. SCR drives a solenoid or a coil or any other drive mechanism of the lock. Final LED (D6) also lights up.

S9 is a blind switch only to fool the inadvertent user. S6 is another clever switch. This lights up LED D5 but also starts a piezo buzzer warning that somebody is fiddling with the lock. A 2200 uF capacitor charges and keeps the buzzer for some time. Use of capacitor is deliberate. It also makes the rogue user take a quick run.

Construction with CMOS IC is simple and straight. The trick here is to lay out the switches in a haphazard sequence, known only to the authorized user. Provision must also be made for easy change of code. With nine switches available, permutations are really many. Wiring must be carefully done to avoid false triggering.

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]]> http://www.engineeringslash.com/digital-ic/electronic-lock.html/feed 0 Three Terminal Adjustable Regulator http://www.engineeringslash.com/power-supply/three-terminal-adjustable-regulator.html http://www.engineeringslash.com/power-supply/three-terminal-adjustable-regulator.html#comments Sun, 25 Oct 2009 10:31:07 +0000 admin http://www.engineeringslash.com/?p=29 Three terminal regulators are just right when we need a single fixed voltage. But they will be cumbersome as a hobbyist works with different voltages at different times and it becomes unwieldy to keep power supplies with a number of three terminal regulators.

Wouldn’t it be better if we have an adjustable but regulated power supply, which can cater to all the voltages we need? And we have such a wonderful device where you can continually adjust your output DC voltage. Well! It is short circuit protected, has only three terminals and all other good things. LM317

LM317

LM317T is an adjustable 3 terminal positive voltage regulator capable of supplying around 1.5 amps over an output range of 1.25 to 37 volts. It also has built in current limiting and thermal shutdown features, which makes it virtually blowout proof. This is an excellent startup project with low ripple. With an easy adjustment of regulated voltage, it can be used as power source for most of the applications in the next chapters. Pin out is given in Figure 13.

Circuit :

Three Terminal Adjustable Regulator

Rectifier part is same as shown in the earlier schematic of bridge rectifier. Transformer is changed to 18 V to get a better range of regulated voltages. 9-0-9 Transformer is used as it is difficult to get an 18 V transformer. Please change transformer rating as per your requirement and the capacitor also for higher voltage rating. It is preferable to use 2200 mfd. caps as larger value makes good, low ripple output voltage.

Pulsating DC output from the bridge is now filtered by the 2200uF capacitor and fed to TN’-put terminal (1) of LM317 regulator. The output of this regulator is varied via the ‘Adj’ pin(3) and the 5K variable resistance or preset pot meter (Rl) connected to it. The regulator uses an internal Zener diode to provide a fixed reference voltage of 1.2 volt across the external resistor R2. Hence the lower end of output voltage is limited to 1.2 volts. C2 is 47uF decoupling capacitor to filter out the transient noise. Metal tab of LM317 is connected internally to the ‘Output’ pin (2). The circuit diagram is shown in Schematic 5.

Construction

Use a small Vero board to fix all the components, cut the tracks where not required and solder the pins. Mount the LM317 regulator on a heat sink. However it can be screwed to the metal case of the enclosure box with the mica insulator and the nylon washer with the mounting screw as shown in Figure 12.

Use a little of heat sink compound on the metal tab and mica insulator as it helps to transfer heat between LM317 and case or heat sink.Use a metal box of suitable size and fix the veroboard and transformer. Mains wire is connected to the primary side of the transformer and taken out. Carefully insulate the mains joints. Mains switch is not shown in the schematic. You may add one if it is required. 5k linear potentiometer is fixed at the casing. Measure the voltages and mark them suitably on a dial fixed on the face of the casing with appropriate indication of the voltage. LED is also fixed on the casing to indicate the power supply.

Use a small Vero board to fix all the components, cut the tracks where not required and solder the pins. Mount the LM317 regulator on a heat sink. However it can be screwed to the metal case of the enclosure box with the mica insulator and the nylon washer with the mounting screw as shown in Figure 12.
Use a little of heat sink compound on the metal tab and mica insulator as it helps to transfer heat between LM317 and case or heat sink.
Use a metal box of suitable size and fix the veroboard and transformer. Mains wire is connected to the primary side of the transformer and taken out. Carefully insulate the mains joints. Mains switch is not shown in the schematic. You may add one if it is required. 5k linear potentiometer is fixed at the casing. Measure the voltages and mark them suitably on a dial fixed on the face of the casing with appropriate indication of the voltage. LED is also fixed on the casing to indicate the power supply.

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]]> http://www.engineeringslash.com/power-supply/three-terminal-adjustable-regulator.html/feed 0 Regulated Power Supplies http://www.engineeringslash.com/power-supply/regulated-power-supplies.html http://www.engineeringslash.com/power-supply/regulated-power-supplies.html#comments Sun, 18 Oct 2009 09:53:06 +0000 admin http://www.engineeringslash.com/?p=22 Unfortunately our hobby circuits work on different voltages and a power supply with single voltage will not be sufficient. Simplest way would be to buy a multi-tapped transformer and connect the voltage taps with a suitable switch. These transformers are available with taps of 1.5,3,4.5,6,9,12V. We need a single multi throw switch (as many throws as there are taps). With 9-6-0-6-9 transformer and with a double pole double throw switch, you can get 6 and 9V DC. With the same transformer, and with a double pole six throw switch, it is possible to get 3, 6, 9, 12, 15, 18 V. Switches and multi-tapped transformers are difficult to procure; cumbersome and even unavailable at some places.

Such schematics are not shown here as there are better ways to build circuits to get variable voltages. Also these power supplies suffer from a major draw back; poor voltage regulation, the voltage falls as more and more current is drawn and voltage also changes with mains voltage fluctuations.

A 12 V power supply shown in Schematic 3 may show as much as 16.8 V without load and it may go down to less than 12 V as the load current is increased. This still can be and is safely used for most of the non-critical circuits, but it is an unstabilised supply.

Why not build a regulated power supply, which doesn’t cost an earth but still gives very good results. Now for the time being, without going into details and complications of integrated circuits, we will use them for the pleasure and ease of using them and build a regulated power supply as a starter.

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