P. Srinivasan, Tanjore, India
5. PROPOSED SYSTEM
5.1 CIRCUIT DIAGRAM
Circuit diagram of proposed system is shown in Circuit Diagram tab2.
5.2.1 POWER SUPPLY MODULE
Power supplies, often referred to as "switching power supplies", use switcher technology to convert the AC input to lower DC voltages. The typical voltages supplied are:
· 3.3 volts
· 5 volts
· 12 volts
The 3.3- and 5-volts are typically used by digital circuits, while the 12-volt is used to run motors in and disk drive fans. We are utilizing for the same, the most cheapest and commonly available energy source of 230v-50Hz and stepping down, rectifying, filtering and regulating the voltage.
184.108.40.206 CIRCUIT DIAGRAM OF POWER SUPPLY
220.127.116.11 STEP DOWN TRANSFORMER
When AC is applied to the primary winding of the power transformer it can either be stepped down or up depending on the value of DC needed. In our circuit the transformer of 230v/15v is used to perform the step down operation. The current rating of the transformer used in our project is 1A.Apart from stepping down AC voltages, it gives isolation between the power source and power supply circuitries.
18.104.22.168 RECTIFIER UNIT
In the power supply unit, rectification is normally achieved using a four silicon power diodes. A commonly used circuit for supplying large amounts of DC power is the bridge rectifier. The components used in this system require 5V and 12V.So the AC voltage should be converted into required DC voltage. This is known as Rectification. For this purpose a rectifier is used.
22.214.171.124 FILTERING UNIT
Filtering ciruits which usually capacitor is acting as a surge arrester always follow the rectifier unit. This capacitor is also called as a decoupling capacitor or a bypassing capacitor.
· An electrolytic Capacitor C1 of 2200MFD / 25V rating is provided at the output of the rectifier circuit as filter.
· 0.1MFD/100V capacitors are provided in the circuit to bypass the high frequency components of the rectified voltage.
· Capacitor C3 470MFD/25V is provided at the output of the regulator to further smoothen the output.
126.96.36.199 VOLTAGE REGULATORS
The voltage regulator play an important role in any power supply unit. The primary purpose of regulator is to aid the rectifier and filter circuit in providing a constant DC voltage to the device. with a regulator connected to the DC output, the voltage can be maintained within a close tolerant region of the desired output.IC7812 and IC7805 is used in this project for providing +12V and +5V DC supply. The LM317, for example, can be operated with the output voltage regulated at any setting over the range of voltage from 1.2V to 37V.Finally resistance is placed in series with LED for its protection and the LED indicates the availability of regulated output supply.
5.2.2 RELAY MODULE
A relay is an electrically operated switch.Current flowing through the coil of the 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 they are double throw (changeover) switches.Relays allow one circuit to switch a second circuit which can be completely separate from the first. There is no electrical connection inside the relay
.Between the two circuits, the link is magnetic and mechanical.
Fig no 5.2.2: Relay module
A transistor is usually used to amplify the small IC current to the larger value required for the relay coil. Relay coils produce brief high voltage 'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode across the relay coil.
The relay's switch connections are usually labelled COM, NC and NO:
- COM = Common, always connect to this, it is the moving part of the switch.
- NC = Normally Closed, COM is connected to this when the relay coil is off.
- NO = Normally Open, COM is connected to this when the relay coil is on.
- Connect to COM and NO if you want the switched circuit to be on when the relay coil is on.
- Connect to COM and NC if you want the switched circuit to be on when the relay coil is off.
188.8.131.52 ULN 2803
Fig no 184.108.40.206 : ULN 2803
The ULN 2803Ahave series input resistors selected for operation. The ULN 2803A is one of the standard Darlington arrays.
§ TTL, DTL, PMOS, or CMOS Compatible Inputs.
§ Output Current to 500 Ma.
§ Output Voltage to 95 V.
§ Transient-Protected Outputs.
§ Dual In-Line Package or Wide-Body Small-Outline Package.
While choosing a relay we should consider the following features:
Physical size and pin arrangement
If you are choosing a relay for an existing PCB you will need to ensure that its
dimensions and pin arrangement are suitable.
The relay's coil voltage rating and resistance must suit the circuit powering the relay coil. Many relays have a coil rated for a 12V supply but 5V and 24V relays are also readily available
The circuit must be able to supply the current required by the relay coil. You can use Ohm's law to calculate the current:
The relay's switch contacts must be suitable for the circuit they are to control. You will need to check the voltage and current ratings.
Switch contact arrangement (SPDT, DPDTetc)
Most relays are SPDT or DPDT which are often described as "single pole changeover" (SPCO) or "double pole changeover" (DPCO).