A clock module with a 16x2 LCD, temperature sensor and backlight control, driven by a Nano. This is a proof-of-concept project and might never be built..
The circuit was originally mocked up in order to demonstrate scrolling the LCD display, but this turned out to be unsuitable, as the persistence of the LCD created a smudging effect that meant that the display was almost unreadable at certain levels of brightness and contrast. Instead, the second line of the display was set to alternate between the date and the temperature.
Arduino Nano
DS18B20 Module (Keyes). The module only adds a series resistor to the
DS18B20 chip.
DS1307 RTC Module
LDS A1050 or similar
BC337 NPN transistor, or similar.
Resistors - 1x1K, 2x10K
LCD display with I2C interface
Arduino Nano, USB cable to suit
Prototyping board and jumper wire
The
Nano I2C interface is wired through to the clock module and the LCD. The
DS18B20 uses a digital single-wire interface that is connected at pin 4,
while the analog reading from the LDR is connected at pin A0. The
brightness control for the LCD is driven from pin 5, through a small NPN
driver BC337.
The LDR is used to dim the display when the ambient lighting falls below a certain level. Only two levels of adjustment are provided, but it would be easy to extend the adjustment to multiple levels.
.
The parts are assembled on a piece of socketed prototyping board. The layout would transfer to a soldered board with pretty much the same payout, using the rails for ground and power and wired interconnects for the signals.
Note the large red dot on the Nano. This has been added to indicate that this device must be configured as 'Old Bootloader' in the Processor Type setting in the IDE. These versions of the Nano devices are perfectly functional, and are often available at a significant discount to the newer versions. The only problem is that the device characteristics are not marked, hence the addition of an identifier.
The
code is an amalgam of several sources, but is essentially the standard
Arduino code for each of the devices. The method of formatting the
numerical values is somewhat cryptic, but is justified in this application
by the simplicity compared with multiple 'if' statements. The LDR
value for switching to dim mode was derived by experiment and will change
with device used and the required brightness. It is possible, of
course, to set the 'bright' setting to something less than 255. The method
of alternating between date and temperature is simple but effective,
although it is technically incorrect at the rollover for the minute. Note
that the size of each array element in the day and month name arrays is 4,
not 3, in order to allow for the trailing zero which is required.
There is code provided in several places which does not allow for this
extra character and therefore creates strange program errors. Note also
that the LCD is not cleared between updates - this is to avoid blinking of
the display. Debugging prints to console are included but disabled,
but console initialisation and monitoring for the date/time setting
function ('u') is functional.
// Real Time Clock with LCD Display.
// RTC I2C at 0x68
// EEProm I2C at 0x50
// LCD I2C at 0x27
// DS18B20 at Pin 4
// Photoresistor at pin A0
// LCD LED backlight control at pin 5
#include <Wire.h> // for I2C communication
#include <LiquidCrystal_I2C.h> // for LCD
#include <RTClib.h> // for RTC
// DS18B20 single-wire temperature sensor library and object.
#include <OneWire.h>
int DS18S20_Pin = 4; //DS18S20 Signal pin
OneWire ds(DS18S20_Pin);
//
LiquidCrystal_I2C lcd(0x27, 16, 2); // create LCD with I2C address 0x27,
16 characters per line, 2 lines
RTC_DS1307 rtc; // create rtc for the DS31307 RTC module, address is
fixed at 0x68
const int LCD_LED = 5; // LCD brightness control (PWM)
/*
function to update RTC time using user input
*/
void updateRTC()
{
//lcd.clear(); // clear LCD display
lcd.setCursor(0, 0);
lcd.print("Edit Mode…");
// ask user to enter new date and time
const char txt[6][17] = { "year [4 - digit]", "month [1~12]",
"day [1~31]",
"hours [0~23]", "minutes [0~59]", "seconds [0~59]"
};
String str = "";
long newDate[6];
while (Serial.available()) {
Serial.read(); // clear serial buffer
}
for (int i = 0; i < 6; i++) {
Serial.print("Enter ");
Serial.print(txt[i]);
Serial.print(": ");
while (!Serial.available()) {
; // wait for user input
}
str = Serial.readString(); // read user input
newDate[i] = str.toInt(); // convert user input to
number and save to array
Serial.println(newDate[i]); // show user input
}
// update RTC
rtc.adjust(DateTime(newDate[0], newDate[1], newDate[2],
newDate[3], newDate[4], newDate[5]));
Serial.println("RTC Updated!");
}
//*************
// Get temperature from DS18B20.
// Replace as required for other sensors.
float getTemp() {
//returns the temperature from one DS18b20 in DEG Celsius
byte data[12];
byte addr[8];
if ( !ds.search(addr)) {
//no more sensors on chain, reset search
ds.reset_search();
return -1000;
}
if ( OneWire::crc8( addr, 7) != addr[7]) {
Serial.println("CRC is not valid!");
return -1000;
}
if ( addr[0] != 0x10 && addr[0] != 0x28) {
Serial.print("Device is not recognized");
return -1000;
}
ds.reset();
ds.select(addr);
ds.write(0x44, 1); // start conversion, with parasite power on at
the end
byte present = ds.reset();
ds.select(addr);
ds.write(0xBE); // Read Scratchpad
for (int i = 0; i < 9; i++) { // we need 9 bytes
data[i] = ds.read();
}
ds.reset_search();
byte MSB = data[1];
byte LSB = data[0];
float tempRead = ((MSB << 8) | LSB); //using two's
complement
float TemperatureSum = tempRead / 16;
return TemperatureSum;
}
//*********************
/*
function to update LCD text
*/
void updateLCD()
{
/*
create array to convert digit days to words:
0 = Sunday | 4 = Thursday
1 = Monday | 5 = Friday
2 = Tuesday | 6 = Saturday
3 = Wednesday |
*/
const char dayInWords[7][4] = {"SUN", "MON", "TUE", "WED", "THU",
"FRI", "SAT"};
/*
create array to convert digit months to words:
1 = January | 6 = June
2 = February | 7 = July
3 = March | 8 = August
4 = April | 9 = September
5 = May | 10 = October
6 = June | 11 = November
7 = July | 12 = December
*/
const char monthInWords[12][4] = {"JAN", "FEB", "MAR", "APR",
"MAY", "JUN",
"JUL", "AUG", "SEP", "OCT", "NOV", "DEC"
};
// get time and date from RTC and save in variables
DateTime rtcTime = rtc.now();
int ss = rtcTime.second();
int mm = rtcTime.minute();
int hh = rtcTime.twelveHour();
int DD = rtcTime.dayOfTheWeek();
int dd = rtcTime.day();
int MM = rtcTime.month();
int yyyy = rtcTime.year();
// Get Temperature
float tc = getTemp();
// Serial.println(tc);
// Get Light Value
int lv = analogRead(A0);
(lv > 800) ? analogWrite(LCD_LED, 255) : analogWrite(LCD_LED,
64);
// Serial.println(lv);
// move LCD cursor to upper-left position
lcd.setCursor(2, 0);
// Create and display time string
String msg = ((hh < 10) ? "0" : "") + String(hh) + ":"
+ ((mm < 10) ? "0" : "") + String(mm) + ":"
+ ((ss < 10) ? "0" : "") + String(ss) + " "
+ (rtcTime.isPM() ? "PM" : "AM")
;
// Serial.println(msg);
lcd.print(msg);
// move LCD cursor to lower-left position
lcd.setCursor(0, 1);
// Create and display date or temp string
if ((ss & 0x4) == 0) {
msg = String(dayInWords[DD]) + " "
+ ((dd < 10) ?
"0" : "") + String(dd) + " "
+
String(monthInWords[MM -1]) + " "
+ String(yyyy)
;
// Serial.println(msg);
lcd.print(msg);
}
else {
lcd.setCursor(0, 1);
msg = " " + String(tc) + " " + char(223)
+ "C " + " ";
// Serial.println(msg);
lcd.print(msg);
}
}
void setup()
{
Serial.begin(9600); // initialize serial
pinMode(LCD_LED, OUTPUT);
lcd.init(); // initialize lcd
lcd.backlight(); // switch-on lcd backlight
rtc.begin(); // initialize rtc connection
}
void loop()
{
updateLCD(); // update LCD text
delay(900);
if (Serial.available()) {
char input = Serial.read();
if (input == 'u') updateRTC(); // update RTC time
}
}
