Introduction

High level Design

The above introduction explains what the basic concept of this project. To handle this concept have to construct four circuits corresponding to the project.

Main circuit

Main circuit means the motherboard of the project. If it tell in another way it is the heart of the Time selectable domestic iron timer. To operate this wants 5 V and it give from the power supply. Main circuit controls all other three circuits.

     Switching circuit

        LCD display circuit

    Power cut circuit

       Power supply circuit

       Port that use corresponding to the circuits

     Hardware construction

        Hardware construction for LCD

Normally LCD has an initial construction. That is six port of LCD directly connect to the PIC 16F877A.Following is the schematic diagram corresponding to the LCD.

        Hardware construction for power cut circuit

For this construction use NPN transistor and it uses as the switch here. When port is 0 V it act as open switch and when port is 5 V it act as close switch.

Relay is the main component corresponding to this daughter card. A relay is an electrically operated switch. Current flowing through the coil of relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and most have double throw (changeover) switch contacts.

Relays allow one circuit to switch a second circuit which can be completely separate from the first. According to iron timer a low voltage battery circuit can use a relay to switch a 230 V AC mains circuit. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil.

As relay has a heating process relay coils produce brief high voltage ‘spikes’ when they are switched off. That is back electromagnetic force and this can destroy transistors and ICs in the circuit. To prevent damage must connect a protection diode across the relay coil.

        Hardware construction for switches circuit

This is full down circuit. So plug out is 5 V and plug is 0 V.

        Hardware construction for power supply

This use to convert 230 V to 5 V and this 5 V is the input to the mother board.

        Software handling

To construct the hardware of this system use ORCAD. For design the schematic diagram use CAPTURE CIS and LAYOUT PLUS use to construct PCB layout.

Programming part is handled by MPLAB IDE and WINPICC 800 use as program compiler.

           Results

The whole process of this project  are control by four buttons.

First on for position select button. There are two position can change and it is for minutes. So user can go to correct position that he wants, using this first button.

Second one for increase position value

According to this I try to change four position. Now it change two position as the difficulty of code.

        Further improvement

        Appendix

        Component list

        Photos

    

                   Switching circuit                                                                                                  Power cut

Whole circuit

        References