High / Low AC Voltage Protection Using PIC Microcontroller

اسلام علیکم من التبع الھداؑ

Hi here is new one Project of PIC microcontroller. In this Project we are making a switch for to protect the Home Appliances from High voltage (Spikes from AC line of Generator or WAPDA etc here in Pakistan) as well as Low Voltage. Specially DC operating devices like Power supplies, adopters and Cell Phone chargers effect from high voltages. 

Working:

When AC Supply rise from 280v or go down from 180v then this Controlling Circuit will cut off the AC supply from the load.

Learning: 

in this Project learning for students is 

1. How to scale down the Max input 

2. ADC Reading

3. Interfacing BJT with PIC controller 

How to scale down the Max input ?

Max readable voltage at the input of ADC are 5v DC. So you have to adjust / scale your values in this range (0 to 5v), in this project lower cut off is 0 & upper cut off is 400 so 

400-0 = 400 

Now you suppose to 400 = 5 so 400/5=80

when AC input change of 80 will make a change of 1v at input of ADC. 

Now wen you Program your values then at 180v is my lower cut off so 180/80=2.25v at input of ADC. Now calculate the ADC reading value in Controller will make it cut. 

ADC Vmax at input = 5v 

ADC bits = 10

Total combinations = 2^10 = 1024

So How many voltage required to change on bit of ADC = 5/1024 => 4.8mv

Now At which value of ADC we will take action to ON or off Relay ?

lower cut off at input ADC= 2.25v 

ADC value 2.25/ 4.8mv = 468.75

468 value we will putt in code to take action.

Same you can calculate upper cut off.

Components list: which's used in this Project.

1. Step down transformer AC 220v to 12v

2. Bridge rectifier

3. Zener diode 5v

4. PIC 16F870 (any PIC which have ADC)

5. Crystal 10MHz

6. 22pf capacitors

7. Resistor for MCLR (1k)

8. BJT NPN 2N3904

9. SPDT/SPST Relay 5v

Circuits Diagram:

Zener Diode: 

Physical shape of zener diode   

 Zener diode always use in Reverse bias in circuit parallel to the load for voltage regulation.

Relays:
here we can use SPST (Single pole single through)or SPDT (Single Pole Double Through) and DPST, DPDT relays are also awailable for different applications.
SPDT relays used in this Project to cut off the AC supply from the load when AC shoot its values.

NPN BJT: Here 2N3904 NPN transistor is used for switch of SPDT relay which use to control or cut off the AC supply when AC shoot from there normal bearable values.

Proteus & MikroC file Download here: