BASIC TIMING TRAFIC CONTROL USING PIC16F877A

Figure 1:

In this mini project we want to design a traffic light which goes through (red yellow green) sequence
The idea of this mini project is to show the basics of PICs.

Things needed

PIC16F877A
Crystal oscillator (any value)
22pf capacitors x2
9V transistor battery
7805 voltage regulator
220uF capacitor
10k resistor(R1)
220 ohms resistor x3
LED (red, yellow, green)

Schematics diagram of the circuit

Figure 2: schematic diagram

Connect the circuit as shown in figure 2, note the led can be connected to any of the I/O pins, that is pins of (PORTA, PORTB, PORTC and PORTD). In this project pin RD7, RD6, RD5 of PORTD was used.

Breadboard circuit

Figure 3: circuit on breadboard

Note some of the connection was done so that it can be well viewed, hence you can put the components wherever you think it might be easy provided the connection are correct.

Steps in the programming

MPLAB IDE from microchip was used to write the source code in C language and compiled with XC8 compiler from Microchip click here to download the IDE from Microchip

The configuration Crystal oscilator was used
(WDTE) we don not want the microcontroller to reset itself for a given time interval hence WatchDog Timer(WDT) off.
(PWTE) Allow a power up time delay by keeping CPU in reset state until the power supply becomes stable.
(BOREN) when the microcontroller voltage supply below a required value; reset the microcontroler.
(LVP) is used for low voltage In Circuit Serial Programming(ICSP) but we will not be using it.
(CPD) is used to if you want to protect your EEPROM from being written to again.
(WDT) is used to to protect your program memory from being written to again.
(CP ) is used to protect the code on your program memory

NB: do not turn ON this configuration CPD, WDT and CP unless you are sure that the data on your RAM or ROM are final.

To start with, we connect our LEDs to RD5,RD6, RD7 we used the #define directive to assign easy to remember words for the bits we connected our leds to. To access bits of PORTD we used PORTDbits.RDx where x is the bit number of PORTD. we then have to make PORTD an output port; this is done by using the TRISD register (TRISD=0x00), PORTD is an output port.
we create an endless loop using the while(1).

The XC8 compiler has inbuilt function for delay that is __delay_ms(x) but it can not exceed a certain limit depending on your Clock rate(frequency of oscillation ). hence we created two delay function using a for loop, one for seconds and the other for minutes.

The source code and the hex file can be downloaded by following the link given at the end of this page.
The hex file was then burn into the PIC with the help of PICKIT2 Replica I bought from Dealextreme

It has a ZIF socket where you can put your PIC inside and program it or connect used the ICSP version by connecting the pins to your microcontroller as shown below

Figure 4: using the ZIF socket to upload code to uC

Figure 5: schematic diagram of how to connect pickit2 to PIC16

Figure 6: HJ-PICKIT2 connected to PIC16

Final output

Figure 7: final output

For this project, looking at the traffic light circuit, one Led light at a
time, which means all of them cannot be on at a time so we can use one 220ohm
resistor for all the led by connecting them as shown below.

Figure 7: alternative for reduction of resistor if one LED comes at a time

Note if you altering the design for other sequence in which two or more LEDs will be on at a time consider putting all the three 220ohm as shown in figure 2.

click to download the SOURCE CODE