Un-interruptible Bench-top DC Power Supply With Display in EMBEDDED

www.spiroprojects.com



How to make your own power supply unit for all your electronics and embedded system experiments. It also has a backup battery which will be used in case of power cuts and a display.
 Components Required
1.     SLA 12V battery
2.     Banana Jack connectors female (2 pairs each)
3.     Screw Terminals (1 pair)
4.     SPST switch (ratings 5A or more)
5.     Adjustable Voltage Regulator LM317 x 2
6.     Voltage regulators 7805, 7809, 7812
7.     GPCBs
8.     Step-down Transformer 16-18V/3 Amps
9.     1N4007 Diodes x 4
10.   Two Relay Module
11.   Capacitors
12.   Resistors
13.   ATmega16/8 Development board
14.  16x2 LCD
15.  Heat Sinks
16.  Enclosure

Features:
Inputs: 220-240V, 50Hz AC
Outputs: 1 X 5V and 1 X 9V (available through banana jack)
1 X Adjustable voltage (available through screw terminal)
Adjustable Voltage Range: 1.25-14.5V in Mains Mode and 1.25-10.5V in Battery Mode
Modes: 1) Battery Mode and 2) Normal Mode (Through Mains)
Automatic Switching and Shutdown by Microcontroller
LCD with various indicators.
 
Block Diagram




Blue line indicates signal lines and black lines indicate power lines.
Let me explain you what each block consists of and its function.
Mains Block: This consists of the transformer, bridge rectifier (4 diodes) circuit and a capacitor. This block takes in the power from a wall socket which provides 220-230V AC. The step-down transformer scales down the amplitude of the sine wave, followed by the bridge rectifier which converts it into pulsating DC which when passing through capacitor yields a unregulated DC power of 16-18V (voltage depends on transformer)



Charger Circuit: This block mainly consists of an adjustable voltage regulator LM317 which along with other components works as constant voltage, current limited charger for our battery. Once the battery is full charged, the circuit automatically supplies low current to the battery and goes into trickle charging mode.



Charge Indicator: This is nothing but two resistors arranged in from of a voltage divider circuit. It scales down the voltage level of battery for the microcontroller to read it.
Relay 1: This is a relay module which switches between the charge indicator circuit and charger circuit depending on the command from microcontroller.
The battery’s +ve terminal is connected to the common pin. The charging circuit is connected to the Normally Open pin and charge indicating circuit is connected to the Normally Closed pin.
When the mains supply is in OFF state, the relay disconnects the charger from battery and connects it to the indicator so that the microcontroller can read the battery level and display on the LCD. When the supply is ON, the indicator circuit is disconnected and the charging circuit is connected to the battery.
Relay 2: This relay module switches between mains supply and battery supply depending on the command from microcontroller.
The battery’s +ve terminal is connected to the Normally OPEN pin and +ve line from main power supply block is connected to the Normally CLOSE pin. The common pin of relay is connected to the DC PSU block.
When the mains are unavailable, the controller automatically switches the relay to battery mode.



Note: The +12V for powering the relay is given directly from the battery. This allows the relay to purely function based on the command from microcontroller instead of availability of power.
DC PSU: This block consists of the voltage regulators and a bunch of capacitors. +5V, +9V and adjustable voltage levels are provided by the ICs 7805, 7809 and LM317 respectively.
The +5V line is also connected to the microcontroller board and LCD.



Note: The +12V for powering the relay is given directly from the battery. This allows the relay to purely function based on the command from microcontroller instead of availability of power.
DC PSU: This block consists of the voltage regulators and a bunch of capacitors. +5V, +9V and adjustable voltage levels are provided by the ICs 7805, 7809 and LM317 respectively.
The +5V line is also connected to the microcontroller board and LCD.



Panel Display: This is the front and outer panel block which consists of the main switch, LCD displaying the voltage level, Potentiometer Knob to adjust the voltage, Banana connectors and screw terminals.
This is how I want it to look like:


The icons on the LCD indicate the following:


 
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