| Traffic Lights usually contain three lamps: red, amber and green. Here is a small project wherein you can control the Traffic Light of a four way intersection using a single controller. Consider four roads ROAD A, B, C and D and their corresponding signals red, amber and green each represented by a LED. So in all there are 12 LED’s each of which is connected to a controller pin.
In this code the duration of all green signals are the same and the duration of all amber signals are same. This duration is defined by DURATION_GREEN which is 10 seconds and DURATION_AMBER which is 2 seconds. For generating delay we will be using Timer 0 in 16 bit INTERRUPT mode to generate One second delay. We load TH0 & TL0 with a specific value & on every clock cycle TH0 & TL0 increments by 1 and when the TIMER overflows from FFFF to 0000 a Timer0 overflow flag is set & interrupt is generated. The maximum delay that can be generated using TIMER 0 in any mode is 65535 clock cycles & since we are using 12MHz crystal the maximum delay is 65.535ms. But we require 1second delay. So we generate 50ms delay using TIMER 0 & when 20 such delays have been generated we come to know that one second has elapsed. So basically 0.05ms X 20 =1 second. So we use a RAM location “multiplier” load it with 20 and whenever the timer overflows the ram location multiplier isdecremented by one. Thus when multiplier becomes zero we come to know that one second has elapsed. Another RAM location “current_signal_duration” is used it contains the total number of seconds for which the current signal has to be turned ON. This RAM location is decremented every time one second has elapsed so when current_signal_duration becomes zero we come to know that it’s time to Turn OFF the current signal and move to the next signal.
//Define the Port PINSa_red bit p0.0 a_amber bit p0.1 a_green bit p0.2 b_red bit p0.3 b_amber bit p0.4 b_green bit p0.5 c_red bit p0.6 c_amber bit p0.7 c_green bit p2.7 d_red bit p2.6 d_amber bit p2.5 d_green bit p2.4
//Define RAM Locations multiplier equ 30h current_signal_duration equ 31h //DEFINE BIT ADDRESS signal_f bit 00h ;if 1 then switch to next signal //DEFINE Constants MULTIPLIER_DEFAULT DATA 20 DURATION_GREEN DATA 10 DURATION_AMBER DATA 2 //TIMER SUBROUTINES timer: push acc push b push psw push dph push dpl clr TF0 mov th0,#3ch mov tl0,#0B0h call check_timer pop dpl pop dph pop psw pop b pop acc reti
check_timer: djnz multiplier,r1_check_timer mov multiplier,#MULTIPLIER_DEFAULT ;One second ended reload value djnz current_signal_duration,r1_check_timer setb signal_f ;signal duration ended move to nxt signal r1_check_timer: ret
//MAIN Program org 0000h jmp main org 000bh jmp timer org 0030h
main: mov multiplier,#MULTIPLIER_DEFAULT setb EA ;Enable Interrupt setb ET0 ;Enable timer 0 Interrupt clr signal_f mov th0,#3ch mov tl0,#0B0h setb tcon.4 ;start timer
loop: mov current_signal_duration,#DURATION_GREEN clr a_green setb a_amber setb a_red setb b_green setb b_amber clr b_red setb c_green setb c_amber clr c_red setb d_green setb d_amber clr d_red
jnb signal_f,$ clr signal_f mov current_signal_duration,#DURATION_AMBER setb a_green clr a_amber jnb signal_f,$ clr signal_f mov current_signal_duration,#DURATION_GREEN setb a_amber clr a_red clr b_green jnb signal_f,$ clr signal_f mov current_signal_duration,#DURATION_AMBER setb b_green clr b_amber jnb signal_f,$ clr signal_f
mov current_signal_duration,#DURATION_GREEN setb b_amber clr b_red clr c_green jnb signal_f,$ clr signal_f mov current_signal_duration,#DURATION_AMBER setb c_green clr c_amber jnb signal_f,$ clr signal_f mov current_signal_duration,#DURATION_GREEN setb c_amber clr c_red clr d_green jnb signal_f,$ clr signal_f
mov current_signal_duration,#DURATION_AMBER setb d_green clr d_amber jnb signal_f,$ clr signal_f ajmp loop $include(timer.inc) End For learning how to interface LED to 8051 microcontroller please click here |
