Construction of Touch Activated Switch Using Microprocessor and Seven Segment Display

Project and Seminar Material For Electrical Electronics Engineering EEE

Abstract

This project work centers on developing a compact apparatus for detecting the touch of a human body and generating a corresponding electrical signal.

A touch detector basically detects a human touch and switches power to a connected load.

The sense signal is generated by sensing a change in capacitance when a person touches a touch pad connected to the sense input circuit.

Chapter One

Introduction

A touch activated switch as the name implies is a device that is activated whenever a sensation of touch is felt by it through a component of its circuitry.

However, this touch activated switch can be constructed using three different things as sensors which are fully explained below;

(1) Metal

in this case, two pieces of metals are connected closely to each other and a wire (cable) is connected to each of the metal while the second terminal of one of the wires is connected to a comparator (op-amp) directly which exist as integrated circuits like operational amplifier (op-amp).A sensation of touch is achieved when a finger is touched on both pieces of metal at the same time and a signal is sent via of one the wires to the comparator which will now use the signal to actualize a purpose by switching another device on.

(2) Wire

Here, the touch activated switch is realized using two cables as sensor in which one of the cables is directly connected to the sensation decoder. Meanwhile, these cables are connected in such a way that when a finger touches two of them the same time, a signal is sent to the comparator via one of the cables which will in turn activate another device.

(3) Light Dependent Resistor (LDR)

This type of sensor is designed with a resistor, in other words it is a type of resistor. In the case of touch activated switch using LDR (sensor), the sensitivity is been determined by a variable resistor. However, using LDR sensor for this kind of project is the best because in this project a high sensitivity is needed. The sensitivity is such that whenever any slite touch is made on the LDR, a signal will be sent to the decoder immediately and the comparator will in turn give an output to switch something on.

Microprocessor

To design an electronic system, one needs to know the difference between a microprocessor and a microcontroller which will enable him to decide which one is the best choice to design an electronic system with.

However, a microprocessor is a central processing unit (CPU) in an integrated circuit which is the core of any microcomputer system. It contains only digital logic circuitry and its most often used to design computers such as laptop and desktop computers.

Meanwhile, a microcontroller is a special-purpose computer system usually programmed to perform a specific task. It is most often used in the design and construction of electronic appliances, automotive electronics and industrial control equipment. Furthermore, a microcontroller contains digital electronics circuitry and analog electronics circuitry.

Finally, a microprocessor operates at a higher speed than a microcontroller. A typical microprocessor will have a clock rate of 1GHZ while a typical microcontroller will have a clock rate of about 20MHZ.

Operational Amplifier (Op-Amp)

An operational amplifier (Op-amp) is a very high gain differential amplifier with high input impedance and low output impedance. In other words an operational amplifier is a solid slate integrated circuit (IC) that uses external feedback to control its functions.

However, an op-amp without any feedback is called “open loop” mode which is actually referring to the so called “ideal” operational amplifier with infinite open-loop gain, input resistance, band width and a zero output resistance. More so, this op-amp has two inputs which are inverting input which is designated by a minus sign (-) and non-inverting input which is designated by a plus sign (+). Meanwhile, these plus and minus signs are not signs of polarity rather they are input terminals.

Furthermore, when the voltage at the two input terminals are the same, the output voltage will be indeterminate. But when the voltage level at the inverting input is greater than the one at the non-inverting input, the output voltage will be low (zero) while when the voltage level at the non-inverting input is greater than the one at the inverting input, the output voltage will be high (VCC).

Chapter Four

Applications

Touch activated switch (touch sensor) has a wide range of application world wide such as touch sensor panels which include wall ovens, washers /dryers, refrigerator and dishwashers.

The durability of the solid- state touch-sensor combined with its strong aesthetic appeal has enabled broad acceptance in wide variety of commercial categories, vending, gaming, fitness and medical.

Touch activated (sensor) is used in various areas in industries E.g. control of machines etc.

Touch sensor is also used by vehicle designer to activate switch and control systems.

Touch sensor is equally used by electronic designers to provide consumer with the latest fingertip control devices like I-pad, touch screen phones (i-phone) etc.

Trouble- Shooting

Trouble- shooting is the act of detecting or finding out faults and as well solving them which is most often applied to repair of failed products or processes.

However, there are two major methods or ways of trouble- shooting an electronic circuit as stated below;
In the first place, an electronic circuit can be trouble- shot by physical observation.
Secondly my trouble-hooting with a multimeter.

Testing

Testing in any design and construction is done or carried out immediately after trouble-shooting or construction.

However, testing is done by connecting the constructed (built) circuit to source of power supply.

Conclusion

There is no assumption that any circuit design /construction is an easy work until it is effectively completed and tested properly functioning. However touch activated switch has many applications domestically and industrially. For instance, it is used in lamp controls and wall switches as well as on public computer terminals.
Meanwhile, touch activated devices that are achieved using

Microcontrollers have many added function like data recording, reading of data from the memory etc.

Conclusively, a touch switch is a type of switch that only has to be touched by an object to operate.

Recommendation

The importance of this project (touch activated switch) cannot be left unlisted because it enables engineer to be absolutely sure of their jobs done effectively and promotes competence as well as strong confidence development in them.

To encourage student to be more serious with their projects, we suggest that the external examiners invited during project defence should recommend scholarship for the students or the groups with an outstanding performance.

Due to the importance associated with touch activated switch, we recommend it to be used in vehicles in a passworded way for security purposes. Also, we equally recommend it to be used in residential buildings and industries.

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