Author Archives: R-B

Lab 1: Flashing an LED

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Description

Today is our first session in PIC microcontroller lab, and we will begin with an experiment that flashes an LED on and off. While this looks very simple it is the best project to start because this makes sure that we successfully wrote the program, compiled it, loaded inside the PIC, and the circuit is correctly built on the breadboard.

In this lab session we will connect an LED to one of the port pin of PIC16F688 and flash it continuously with 1 sec duration.

Required Theory

You must be  familiarized with,

  • digital I/O ports (PORTA and PORTC) of PIC16F688
  • direction control registers, TRISA and TRISC
  • special function registers CMCON0 and ANSEL

If you are not then please read this first: Digital I/O Ports in PIC16F688.

Circuit Diagram

To our basic setup on the breadboard (read Getting Ready for the First Lab), we will add a light-emitting-diode (LED) to port pin RC0 (10) with a current limiting resistor (470 Ohm) in series. The complete circuit diagram is shown below.

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Lab 2: Basic digital input and output

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Description

Today we will learn how to read digital inputs from a push button switch. A digital input has only two values: 1 and 0. The configuration of the push button switch is same as that of the reset switch except it goes to a different port pin. The status of the switch will be read through RC1 and every time when it is pressed, an LED connected to RC0 will be toggled ON and OFF.

Required Theory

You must be familiar with the digital I/O ports of PIC16F688 and their direction settings. If you are not, read Digital I/O Ports in PIC16F688.

Circuit Diagram

To our last setup (see Lab 1: Flashing an LED), connect a push button switch to RC1 as shown below. The input ports of a PIC microcontroller have very high input impedance, and therefore, during normal condition when the switch is open, the RC1 pin is pulled ‘High’ through the external 10K resistor. When the switch is pressed, RC1 is pulled to ground and the microcontroller will read it as logic ‘Low’. In this way, a simple push button switch with a pull-up resistor can be used to provide digital inputs (1 and 0) to the microcontroller. Read more

Getting ready for the first lab

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This is to be followed after you have successfully completed the following steps:

Basic setup on the breadboard

As mentioned before all the experimental circuits will be constructed on the breadboard because it is easy to modify the circuit and correct any wiring error. Figure 1 shows the pin diagrams of PIC16F688. It is a 14-pin microcontroller with a precision internal oscillator. It provides 12 I/O pins with individual direction control, and can drive LEDs directly. 8 out of 12 I/O pins also serve as ADC channels for the internal 10-bit ADC. The various features of PIC16F688 will be discussed later in more detail in following lab sessions. For now, we will look at a simple circuit setup for PIC16F688 on the breadboard that will be used in all the experiments.

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