Spency's digital-diy 18F PIC micro Tutorial

18F LED Example

LED's are great as indicators, and are very easy to interface with. PIC's can produce around 25mA on an output. This is much more than most logic outputs will deliver, and it helps to interface with many devices, especially simple LED's that only require 5mA-20mA usally.

Here's a simple program that will turn an LED on and off twice a second in Swordfish;

Device = 18F4520
Clock = 8
Config OSC = INTIO67                // Use the Internal Oscillator

Include "utils.bas"

Dim LED As PORTA.0                  // Assign an alias for "LED"

// Start Of Program...
OSCCON = %01111111                  // Sets up the internal oscillator
SetAllDigital                       // Make all Pins digital I/O's
Low(LED)                            // Make the LED pin an output and set it low

While True

    LED = 1                         // Turn on the LED
    
    DelayMS(500)                    // Delay for half a second
    
    LED = 0                         // Turn off the LED
    
    DelayMS(500)                    // Delay for half a second
    
Wend

The wiring diagram is as follows

Note the PIC's power supply/oscillator are not shown

Your LED will have a predefined forward voltage and current, which can be found from the supplier your buy it from. You need to use this forward voltage to calculate the series resistor required. Say for example, my LED had a Vf of 2.0 volts, and and If of 20mA(forward current) . This means that the series resistor needs to drop 3V and yet allow 20mA to pass through it. Simple maths allows us to calculate exactly what resistance we need.

Ohms Law: V = IR
Therefore R = V/I

And if R = 3/0.020
Then R = 150 ohms

Now you know that the series resistor must be 150 ohms or greater to safely run your LED.

Where you can get the components;