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Push Button Electronic Switch with ON-OFF Feature

Posted Jan 14, 2012 at 9:25 am

Figure 1 

The circuits was designed to illustrate the different functionality of an ON-OFF electronic switch the uses a push button mechanism.

• Electronic Switch – a device or component used to connect or break a circuit by interrupting or diverting the current from one conductor to another
• Inverter – a device that converts direct current (DC) to alternating current (AC) wherein the use of control circuits, switching and transformers can set the frequency and voltage of the resulting AC
• RS Flip Flop – the reset and set operation that is constructed form a pair of joinedNOR gates where the outputs are connected to the other NOR input gates and functions as a simple memory element
• JK Flip Flop – the most versatile of the basic flip flops because it can be configured to work as an RS flip flop, a T flip flop or a D flip flop
• D Flip Flop – considered as a basic memory cell, delay line, or zero-order hold where output always takes the state of the input at the moment of a rising clock edge
• T Flip Flop – also known as toggle flip flop where the output changes on each clock edge providing an output that is half the frequency of the signal to the input

Circuit Explanation

Three circuits have been sampled that utilizes the push button mechanical switch which are so called due to their activation method, which is usually in the form of a plunger that, when pressed, opens or closes the switch. CMOS gates are presented by developing the high resistance of entry by the switch. The first representation of the gates is shown on figure 1, where the operation of RS flip flop corresponds to the actions of the two NANDgates or NOR gates. These gates can be considered as universal gates their combination can be regarded as an AND gate, OR gate, and an inverter and can also be used to achieve the basic operations. Since this is an AND gate with an inverted output, its output is true if NOT all inputs are true, coming from two or more inputs. A flip flop refers to a bistable multivibrator circuit that serves a bit of memory and has two stable states. The cross coupling and construction of the NAND gates produces an RS flip flop that is normally used in storage mode for having reset and set inputs.

Pressing the switch S1 will cause the output 3 to become high and will be latched at this state. Only when pressing switch S2 will change the status of the circuit where output 3 will become low while making output 4 to become high. The operation can be maintained by connecting a capacitor with a value of 100 nF. The inputs will always produce a logic low to the equivalent output.

The second figure illustrates the operation of an inverter CMOS. In this type of design, in the event that the input is high, it will always produce a corresponding low output while the resistor R is being connected to the supply to control the incoming voltage to the inverter IC. To produce an opposite logic operation, the switch S2 should be connected to the supply while the resistor R to be connected to the ground.

In figure 3, the same logic operation as with figure 2 is illustrated with replacing the IC2 with a NOR or NAND gate. This would yield to the same result as with figure 2 having an inverted output. In figures 2 and 3 scenario, the output does not remain constant because the output changes upon unpressing the switch button. To be able to maintain the output, a JK flip flop, D flip flop or T flip flop should be connected after the IC2 and IC3. These flip flops can change the operation of the circuit especially the function of the switch for momentary switching.

The contacts of all the switches can be replaced with contacts while also replacing the resistor R with a value of from 100K ohms to 10M ohms. In the case that contacts are used instead of switches, the effect of noise would be noticeable at these stages. However, the noise can be minimized by placing a capacitor with a value of 100 nF, connected in parallel with the contacts.

In choosing a switch, three important features have to be considered such as contacts, ratings, and method of operation. The contacts of the switch are described by the quantity of switch contact sets known as pole; the quantity of conducting positions, may it be single or double known as throw; by the quantity of conduction positions, may it be three or more known as way; by the ability of the switch to return to its normal position when released known as momentary; by the ability of the contact not to conduct or inOFF position known as open; and by the ability of the contacts to conduct in several positions in the ON position known as closed. The rating of the switch contacts can be regarded as maximum current and voltage which can also be different in the ratings for AC and DC. Since the current falls to zero several times, the values of AC are higher while across the switch contacts is less likely to form an arc. For inductive loads like motors and coils, the maximum current is less because more sparking is caused by them when switched OFF at the contacts.

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

Tags: push button, electronic switch, on/off,