Automatic Emergency Light

This is the simple circuit of automatic emergency light. It is called dark dependent circuit. A 555 timer IC and LDR is used for this configuration. When light fall on the LDR, its resistance is decrease and in dark position its resistance is going high. Using these characteristics of LDR, automatic emergency light is made.

Automatic Emergency Light Circuit diagram:

LDR is called Light Dependent Resistor. Its resistance is inversely proportional to the falling light on its surface. In dark, its resistance is approximately 7k to 10k. When light fall on its surface, its resistance is decrease to less than 1k. In the circuit, a voltage divider arrangement circuit is used here with LDR and 10K variable resistor.

When light fall on the surface of LDR, the resistance decrease to 1k. So the voltage of the timer pin-6 is greater than 2/3 of +Vcc. For this reason the output pin-3 goes low. The base voltage of transistor BC547 is less than 0.75 volt. The transistor is OFF state. So the light is OFF. In dark position the LDR resistance increase is high so the voltage of the trigger pin-2 decrease to less than 1/3 of +Vcc. The output pin-3 goes high so the base voltage of the transistor BC547 is greater than 0.75 volt. The transistor is ON state. So the light is ON and it emits light.

Source: http://www.ecircuitslab.com/2012/06/simple-automatic-emergency-light.html

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Automatic Mains Disconnect Circuit

Downloading and CD-burning programs usually provide the option of automatically shutting down the PC on completion of their tasks. However, this energy-saving feature is of little benefit if even after the PC has been switched off, all of the peripheral equipment remains connected to the mains and happily consumes watt-hours. The circuit shown here provides a solution to this dilemma. It is connected ahead of the power strip and connects or disconnects mains power for all of the equipment via a power relay. A connection to a 12-V PC fan (which may be the processor fan or the fan for the chipset, if the latter is present) indicates whether the PC is switched on.

If you are certain that the 12-V power supply voltage is switched off when the PC is in the sleep mode, you can use this connection instead. To switch everything on, press the Start button to cause the power relay to be energized and provide mains voltage to all of the equipment. If the PC has an ATX board, its Power switch must be pressed at the same time to cause the PC to start up. When the PC fan starts to run, low-power relay Re1 engages and takes over the function of the Start switch, which can then be released. This state is stable. If the PC switches to the sleep state, the 12-V voltage drops out.

The electrolytic capacitor ensures that Re1 remains engaged for a short time, after which it drops out, followed by the power relay. D1 prevents the electrolytic capacitor from discharging through the connected fan, and D2 is the usual freewheeling diode. The system is disconnected from both mains leads and is thus completely de-energized. Be sure to select components that are suitable for their tasks. Naturally, the contacts of Re2 should be rated to handle the total current drawn by all of the peripheral equipment and the PC, and the relay coil must be suitable for use with mains voltage (6 mm minimum separation between coil and contacts).

A low-power 12-V relay that can switch mains voltage is adequate for Re2. The Start pushbutton switch is connected to the mains voltage, so a 230-V type must be used. The circuit board layout and enclosure must also be designed in accordance with safety regulations. A separation of at least 6 mm must be maintained between all components carrying mains voltage and the low-voltage components, and the enclosure must be completely free of risk of electrical shock. With a bit of skill, the circuit can be fitted into a power bar with a built-in switch, if the switch is replaced by a pushbutton switch having the same mounting dimensions.

Note:

• The circuit is not suitable for use with deskjet printers that can only be switched on and off by a front panel button.

Source : www.extremecircuits.net

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9V Automatic Battery NiCd Charger

This automatic NiCd charger for 9V NiCd batteries is using 555 timer properties and is very easy to build. Why is an automatic 9 volts NiCd battery charger? Because you can leave the battery for charging as much as you like: it will be always completely charged and ready for use when is needed. It wont be overcharged and it will not discharge.

9V Automatic Battery NiCd Charger Circuit Diagram :

With the values presented in the circuit diagram, the battery charger NiCd circuit is suitable for 6V and 9V batteries. 9 volt types with 6 and 7 cells are charging with 20mA; P1 must be adjusted so that the NiCd charger disconnects after 14 hours. Window inferior level is set at 1V below this value with P2. 5V battery type with 4 or 5 cells are charged at 55mA. Again, with P1 adjust the NiCd charger circuit so it disconnects after 14 hours. Window inferior level must be set at 0.8V below this value.

Source: http://www.ecircuitslab.com/2012/08/9v-automatic-battery-nicd-charger.html

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