How to build an auto off bedside lamp

At night, while you're asleep, if an electricity failure occurs, you are caught in the dark, and when you attempt to get up and walk to the entrance door from the bed, you will experience a Herculean task to reach the door without hitting any object on the way. In such situations, a torchlight may be handy. But it will be sometimes cumbersome to search in the torchlight and even to get proper light from the torch at that crucial time. This may be because the battery is down, or it may not work properly, leaving you in the dark. Hence, hands-free adequate light support is beneficial in such circumstances. Such a gadget is automatic with an auto off facility, just beside your bed is an ideal position. This is what we are going to study in this post that how you yourself assemble this versatile gadget, which operates on a low-power battery.   

Know your circuit

The gadget is nothing but an 'Auto off bedside lamp'.    

The circuit schematic is shown here. It is a very simple circuit with very few components associated with the CMOS IC 7555. 

Parts List

IC1- 7555 ........................................... .1 no.

T1 - BFY50 Transistor .............................1 no.

La1 - Lamp 3V, 200mA............................1 no.

C1 - 220 MFD 16V electrolytic capacitor----1 no.

R1 - 1M ohm resistor .............................1 no.

R2 and  R3- 4.7M ohm resistor.................2 nos.

R4 - 1K ohm resistor...............................1 no.

Battery - 4.5V .......................................1 no.

on/off - touch sensor .............................1 no. 

Know your design

The circuit is built around the CMOS IC 7555. To switch on the lamp on/off sensor pad is used. Touch the sensor simultaneously with your finger on both the portion on and the (centre) earth portion. The lamp is illuminated. If you touch off and earth simultaneously, the light switches off.  Pin 4 and 2 are connected to the sensor pad for on/off action. Touching the sensor pad triggers the IC to activate the transistor T1 through the output pin 3 of the IC. R2 and R3 are the biasing current paths from the power supply. 

Once triggered, the light will automatically switch off after a 5-minute duration. The timing action is controlled by the RC network connected to pins 6 and 7. Here, R1 and C1 act as the time setting components.  If one desires to change the timing interval for auto off, the values of either R1 or C1 can be changed and set accordingly. 

A positive power supply of 4.5V is given to pin no. 8, while pin is grounded. i.e., connected to a negative power supply.  T1 transistor controls the current taken by the 3V bulb, which normally consumes 50 mA while in operation. However, a 200mA bulb is connected. 

If one wants more power and brightness, a slightly higher wattage bulb can be used in La section. However, the T1 transistor should be protected with an appropriate heatsink to handle high current. 

The circuit shuts off the light after 5 minutes of switching it on. If one wants to shut the lamp off before 5 minutes of duration, it can be done by touching the sensor to the off position.    

Know your assembling

The circuit can be easily assembled on a general-purpose printed board. One can try the circuit even with a solderless breadboard for simplicity of assembly. Electronics students, hobbyists and electronics enthusiasts show more interest in assembling this circuit for utility value and for building experience.  

For your convenience of assembling the sensor portion of the PCB for on/off switch is given here, so that one can have an idea how to construct the sensor plate. A small portion of the copper-clad board is used for the sensor pad making. 

A complete parts list is given. As the components are easily available and cost very little for the project construction. Hence, it is a low-cost circuit assembly gadget useful for many. 

Conclusion

I would like to have feedback from the builders, so that the project can be improved and promoted to many. Please give your comments here about this post and we shall meet you again with some other interesting project shortly.