PIC18F4550 ADC Simple Digital Volt Meter

The ADC module of PIC18F4550 could read an analog input voltage up to 5 V DC with some DC offset. However, the outside analog voltage fed to the ADC could be greater than 5 V DC by adding a simple voltage divider circuit. 

The voltage divider circuit is very simple, built by two resistors in this case. The output voltage from the divider circuit is smaller than the input according to the dividing factor. The factor created by picking up a different resistances of the selected's. The designer may decide and take a little math calculation using voltage divider theorem to get a specific division factor. 

I don't show the overall process of math calculation here. You can see this post to get a full detail.

The MCU reads the analog input voltage fed to RA0.

PICC Source Code

Schematic Diagram

Schematic Diagram

Click here to download the zip file of this example.

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ATMega16 ATMega32 Experiment Board PCB from PCBWay

 

PIC18F4550 DS1307 I2C RTC LCD Interfacing

PIC18F4550 has a master synchronous serial ports (MSSP) module inside. This module consist of two sub-communication modules - I2C and SPI. An I2C is communication protocol for short range, low data rate requires only two pins - Serial Data(SDA) and Serial Clock(SCL). However, the SPI communication port doesn't lists here.

DS1307 is a real time clock keeper with I2C communication interface. This device keep the time running by an external crystal clock of 32.768 kHz. Even the supply voltage is off, a coin back up battery keep the data RAM synchronizes for future use. Since an I2C is use for communication, there are two communication pins - SDA and SCL. These two pins are open drain, require an individual external pull up resistor. The resistor ranges from 4.7 kOhm to 10 kOhm resistance.

For more technical details about DS1307, please see this post on another blog I wrote.

In this programming example, PIC18F4550 uses its I2C master to write and read timing data from DS1307 I2C slave device. Those data will display on a character display.

Circuit Simulation

PICC Source Code

Schematic Diagram

Schematic Diagram

Click here to download the zip file of this example.

A DIY TWI LCD Using PCF8574AP For Arduino

A character LCD with a 44780 LCD controller generally controlled by an MCU parallel port. Even the data transfer in-used is 4-bit mode, but it still require up to six MCU pins. 

A character LCD with PCF8574AP

PCF8574AP is an 8-bit general purpose digital I/O expanding. We can read and write digital data between this device and a master MCU, or even controlling a parallel LCD module. However using an I2C IC bridge the master MCU uses only two pins of its digital I/O to interface to the LCD.

In online market the PCF8574AP is built in module the a character LCD that cost a few Dollars. For an electronics hobbyist like me, I only bought a single DIP version of this chip. I can program it to read/write digital data before I decide to put it with a character LCD.

I decided to make my own I2C board module for my Arduino Uno board. This design follows the liquidCrystal_I2C LCD library from an author on GitHub. The overall design is not difference from the original one's but I made my own schematic and PCB design for my personal use.

I use Eagle CAD from Auto Desk software due to its richness of symbols and footprints library. The result yield with a small rectangular PCB module wired with PCF8574AP and a character LCD.

Schematic Diagram

PCB View

This design example is fully worked as I have tested it with Arduino Uno using its library.

A zip file of this design could be download here.

Connection Diagram

 

This Arduino sketch is from the library itself with some of my own modification.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// set the LCD address to 0x38 for PCF8574A with A0 A1 A2 wired to GND
LiquidCrystal_I2C lcd(0x38,16,2); 
void setup()
{
  // initialize the lcd
  lcd.init();                     
  lcd.backlight();
  lcd.clear();
  Serial.begin(9600);
  lcd.setCursor(0,0);
  lcd.print("Serial Port LCD");
}

void loop()
{
  // when characters arrive over the serial port...
  if (Serial.available()) {
    // wait a bit for the entire message to arrive
    delay(100);
    // clear the screen
    lcd.clear();
    // read all the available characters
    while (Serial.available() > 0) {
      // display each character to the LCD
      lcd.write(Serial.read());
    }
  }
}

This sketch could be download here, or you can get from the library after the installation.