ON/OFF Featured Touch Switch by 555 Timer

Figure 1 

The circuit was designed to create a touch switch that can be used for ON/OFF functions in modern technology.

• BC547 – NPN small signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selections
• 555 – a highly stable device for generating oscillation or accurate time delays used in pulse width/position modulation, sequential timing, time delay generation, linear ramp generator, precision timing, and pulse generation due to its features such as normally open and normally off output, temperature stability, output and supply TTL compatible, adjustable duty cycle, and operates in both astable and monostable mode

The early technology of switches has been improved in the construction of this circuit. However, the transformation took more testing, replacement of old switches, and checking of larger currents rather than the stability. Having a modern look will also account to the transformation. Behind the assembly of the circuit lies several reasons of its essential use in the market. The materials used are abundant anywhere and the manufacturing process is very simple.

The integrated circuit 555 timer was the main component in this circuit since it is easy to use with most electronic circuits. It is very cheap due to its popularity in the electronics world. They have several versions that are available in use for extreme temperatures and low current applications. In this circuit, the relay is being driven by the 555 timer IC where the contacts are vital in the operation of the switch. The metal surface can be formed in the desired shape but should be kept clean and close to the circuit. A soft touch on the two plates from a user is enough to cause a change in the state of the circuit.

The ON state occurs as the contacts of RL1 closes which corresponds to the plate JF1 while the OFF state occurs in the open contacts of RL1, will correspond to the plate JF2. The amount of current in RL1 will depend on the status of the contacts. The red LED D2 will turn ON simultaneously as the switch conducts in the event of RL1 contacts being closed.

Figure 2 

One of the interesting applications of this circuit is for hard to reach cords and switches like the Christmas ornament switch, where the light turns ON/OFF with a touch ornament. In industrial areas, touch switches can be most useful in detecting levels, line control of conveyor, stopping machineries, and detecting parts. Commercially available lamps are also incorporating the function of touch switches. In computer technology, the touch switch is used to turn ON the Apple LCD displays.

Source:users.otenet.gr/~athsam/touch_switch_on_off.htm