A simple controller for ventilation fan was made by using a PIC16F84 chip. A 5k variable resistor provides latching input for time on setting. RB2 and RB1 are activated to logic '0' every 10 min. The variable resistor, 5k, is used to set the period of logic '0' ranging from 1 min to 10 min.

RB1 && RB2  ____         _______________~___________________        ______
                              _____                                                               _____
                              <---------------------- 10 min ------------------------->
                              <-----> 1-10 min

The controlled program was written in BASIC, and was compiled by BASIC compiler. The HEX file of the following program is fan.hex.

 
'/---------------------------------------------------------------------
'/      PROGRAM for VENTILATION FAN CONTROLLER **
'/         AUTHOR:  JAROON KEAWKHRUA
'/                   START   14/10/2542
'/                   UPDATE 14/10/2542
'/        modified from PIC CLOCK.BAS
'/---------------------------------------------------------------------

        Include "bs1defs.bas"

sout    var     portb.3
minute  var     byte    ' Define minute variable
second  var     byte    ' Define second variable
ticks   var     byte    ' Define pieces of seconds variable
update  var     byte    ' Define variable to indicate update of LCD
        th        var     word
        vr        var     word
        comp      var     word
        sen       var     portb.0

        serout sout,n9600,["Hello",10,13]
        minute=0 : second=0 : comp=0
        high porta.2
        low portb.1
        low portb.2

        update = 1      ' Force first display

' Set TMR0 to interrupt every 16.384 milliseconds
        OPTION_REG = $d5        ' Set TMR0 configuration
        INTCON = $a0            ' Enable TMR0 interrupts
        On Interrupt Goto tickint
 

' Main program loop - in this case, it only updates the LCD with the time
mainloop: If update = 1 Then

                ' Display time as hh:mm:ss
SENT:      HIGH SEN
           PAUSE 1
           RCTIME SEN,1,TH   ' use RC time instruction to read POT resistance
            vr = th*8
           vr = vr+50
           if comp => vr then
                low porta.2
                high portb.1
                high portb.2
           endif

           serout sout,n9600,[#minute,":",#second," ",#vr," ",13]  ' used during debugging
                update = 0      ' Screen updated
        Endif

        Goto mainloop
 

' Interrupt routine to handle each timer tick
        disable         ' Disable interrupts during interrupt handler
tickint: ticks = ticks + 1      ' Count pieces of seconds
 
        If ticks < 61 Then tiexit       ' 61 ticks per second (16.384ms per tick)

' One second elapsed - update real-time clock
        ticks = 0

        comp = comp + 1

        second = second + 1
        If second >= 60 Then
                second = 0
                minute = minute + 1
                If minute >= 10 Then
                        minute = 0
                        comp = 0
                        high porta.2
                        low portb.1
                        low portb.2
                Endif
        Endif

        update = 1      ' Set to update LCD

tiexit: INTCON.2 = 0    ' Reset timer interrupt flag
        Resume

Last updated, 16 October 2542