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A PIC16F819 DYMOCLOCK

I wanted to build a clock as simple as possible : built around a little 18 pins PIC no 7 segment display, only LEDs no decoder, no buffer, no driver for...

Circuit diagram
Tags: #clock#dymo#pic16f819
Ibrar Ayyub By Ibrar Ayyub
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At a glance

CategoryLED Projects
PIC modelPIC16F819
IncludesCircuit diagram
Reading time~3 min

Summary of A PIC16F819 DYMOCLOCK

This project is a simple LED clock and thermometer built around a PIC16F819 (18-pin) using direct LED driving (no decoders/drivers), 27 LEDs arranged in three rows for hours, minutes/seconds/°C, and fine increments, plus a silicon diode as temperature sensor. It runs a 12-hour clock with 2°C thermometer resolution, multiplexed LED tables, and button controls for mode, toggle, and set; compiled with mikroC for a PIC16F819 at 16 MHz.

Parts used in the Simple LED clock with thermometer:

  • PIC16F819 microcontroller (18-pin)
  • 16 MHz crystal
  • 27 LEDs (25 mA each)
  • Silicon diode used as temperature sensor
  • Push buttons (mode, toggle/advance, set)
  • Colored hookup wires for LED wiring
  • Power supply (suitable for PIC and LEDs)
  • Miscellaneous PCB or protoboard and wiring hardware
I wanted to build a clock as simple as possible :
  • built around a little 18 pins PIC
  • no 7 segment display, only LEDs
  • no decoder, no buffer, no driver for the LED display
  • a cheap temperature sensor

The solution of direct LED driving comes from a Microchip Application Note AN234, and as I'm using 25 mA LEDs, I simply removed all current limiting resistors.

A PIC16F819 DYMOCLOCK A silicon diode is used as temperature sensor, and the rest of the circuit is very classic around a PIC16F819 :
Upper row : hours
Middle row : minutes or seconds or degrees C
Lower row : add it to middle row
The wiring side of the LEDs is a little bit messy,

some colored wires are helpful !
See the source code for LED numbering.

THE SOURCE CODE
*************************************************************************
 * file         : dymoclock.c
 * project      : Simple LED clock with thermometer
 * author       : Bruno Gavand
 * compiler     : mikroC V6.0.0.0
 * date         : september 15, 2006
 *
 * description  :
 *      This is a 12 hours clock with 27 LEDs display, with a 2°C resolution thermometer
 *
 * target device :
 *      PIC16F819 with 16 Mhz crystal
 *
 * configuration bits :
 *      HS clock
 *      no watchdog
 *      no power up timer
 *      RA5 as MCLR pin
 *      brown out detect
 *      LVP disabled
 *      data EE protect disabled
 *      ICD disabled
 *      CCP1 pin on RB2
 *
  *************************************************************************
 */
/*
 * display modes
 */
#define MODE_HOURMN     0       // display hours:minutes
#define MODE_SS         1       // display seconds
#define MODE_TEMP       2       // display temperature
#define MAX_MODE        3       // number off display modes
/*
 * buttons
 */
#define BUTTON          ((PORTA.F1 == 0)  || (PORTA.F2 == 0))   // at least one
#define BUTTON_MODE     (PORTA.F1 == 0)                         // mode / advance
#define BUTTON_TOGGLE   (PORTA.F2 == 0)                         // toggle / valid
#define BUTTON_SET      ((PORTA.F1 == 0) && (PORTA.F2 == 0))    // both at the same time
#define TEMP_REF        115     // silicon junction offset : 600 mV
#define MAX_TEMP        20      // number of temperature samples
/*
 * LED multiplexing tables
 *
 * LED index   : 1 2 3 4 5  6 7 8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
 * LED number  : 1 2 3 4 9 10 5 6 11 12 25 30  7  8  5 10 35 40 45 50  2  1 15 20  3  4 55
 * LED hours   : 1 2 3 4 5  6 7 8  9 10 11 12
 * LED min/deg :                               5 10 15 20 25 30 35 40 45 50 55
 * LED 1234    :                                                                1  2  3  4
 */*
 * upper row : hours from 1 to 12
 */
const   unsigned char hhTable[] = { 0, 1, 2, 3, 4, 7, 8, 13, 14, 5, 6, 9, 10 } ;
/*
 * middle row : minutes/seconds/°C from 5 to 55 step 5
 */
const   unsigned char mnTableH[] =
        {
        0, 0, 0, 0, 0,
        15, 15, 15, 15, 15,
        16, 16, 16, 16, 16,
        23, 23, 23, 23, 23,
        24, 24, 24, 24, 24,
        11, 11, 11, 11, 11,
        12, 12, 12, 12, 12,
        17, 17, 17, 17, 17,
        18, 18, 18, 18, 18,
        19, 19, 19, 19, 19,
        20, 20, 20, 20, 20,
        27, 27, 27, 27, 27        } ;/*
 * lower row : increment of minutes/seconds/°C from 1 to 4
 */const   unsigned char mnTableL[] =
A PIC16F819 DYMOCLOCK Schematic        {        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26,
        0, 22, 21, 25, 26
        } ;
/*
 * RAM variables
 */
unsigned char   mode ;                  // display mode
unsigned char   toggleMode ;            // toggle mode flag
unsigned int    scaler = 0 ;            // timer overflow divider
unsigned char   hh = 1 ;                // hours
unsigned char   mn = 1 ;                // minutes
unsigned char   ss = 0 ;                // seconds
int             temp ;                  // temperature in °C
unsigned char   tdeg[MAX_TEMP] ;        // array of temperatures samples

unsigned char   tidx = 0 ;              // index of the temperature sample

 

For mroe detail: A PIC16F819 DYMOCLOCK 

  • What microcontroller is used in the project?
    The project uses a PIC16F819 microcontroller.
  • How many LEDs are used for the display?
    The display uses 27 LEDs arranged in three rows.
  • Does the design use LED drivers or decoders?
    No, the design drives LEDs directly without decoders, buffers, or drivers.
  • What component is used as the temperature sensor?
    A silicon diode is used as the temperature sensor.
  • What clock format and thermometer resolution does the project implement?
    It implements a 12-hour clock and a thermometer with 2°C resolution.
  • What compiler and clock speed are specified for the PIC?
    The source is compiled with mikroC and targets a PIC running at 16 MHz.
  • Are current limiting resistors used for the LEDs?
    No, current limiting resistors were removed because 25 mA LEDs and Microchip AN234 direct drive technique are used.
  • How are different display modes selected?
    Buttons on PORTA are used: one for mode/advance and one for toggle/validate; both together act as set.
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Ibrar Ayyub

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough...