INTRODUCTION :
THE heart of this project is the microcontroller with value pic16f877a of microchip by manufacturer and 8bit in terms of bit category
It has 40pins of which pin 12&30 are vdd ,pin 13&31are vss and pin 1 is MCLR which must be connected in respect to vcc
For the program loaded into the program memory to be executed the must be an oscillator with frequency stability thus a crystal oscillator with 8Mhz is choosen and according to the pdf 30pf capacitor must be connected to it as depicted in the pdf
The remaining 35 pins can either be set as input or output ports by the use of the TRIS key word
The automatic water control have a power section which consist of transformer, bridge diode ,capacitor and the voltage regulator .
The transformer takes an input voltage of 220vac and step it down to 12 volts ac
This 12vac is passed through the rectifier and being converted to vdc before passing through the filter capacitor (25 by 4700uf)which takes off ac ripples leaving behind dc signal this signal is passed through a voltage regulator of 5v(7805) and then filtered again by another 470uf capacitor by 25 v thus this voltage is feed into the microcontroller.
PORTB of the microcontroller is interfaced with 16x2 lcd which is being configured in four bit mode as described by its pdf
The contrast of the lcd is adjust using a 10k ohms variable resistor
However PORTB was specified as an output port from the software program
The anode of output led for indicating the water are interfaced to PORTC while their cathode is grounded. The signal interface with the motor relay is taken from PORTC RC1 baising the base of TIP41 transistor through a 1kohms resistor . the transistor is connected in common emitter mode
However a clapping diode is connected across the relay the trap any stray voltage that might destroy the transistor
A 470uf capacitor is also connected to the relay for charge storage so as to trap ripple with switching.
Recall that for a transistor to be properly biased the base emitter junction must be forward biased while the collector base junction is reversed biased .
Four set of transistor are labeled Q2,Q3,Q4 and Q5 are biased in common emitter mode, which all the collector are conneted to a 57k ohms resistor thus acting as a transistor NOT gate (ie a high at the base of the transistor will bring a low in the output vise visa) . this transistor are biased with 12vdc from the rectifier.
NOTE : the probe carrying the vcc from the rectifier must be placed in the over head tank first before any other % probe.
It was also noted from practical test that the resistance of water when measured with multimeter was about 130-160 k ohms
From the relay the common of the relay is connected to live of ac voltage and the normally open to the live terminal of the pumping motor, while neutral is common to all.
The switch is used to make and break the circuit .
Code for water level
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