Clock with LCD and PIC 18F4620 v. 2.02

Summary characteristics

• 24h time clock with LCD 4 lines x 20 characters.

• Line 1: day, month, and year, Line 2: day of the week (eg Mon for Monday), hours, minutes and seconds, Line 3: if any party or birthday and setup menus are displayed as a description of the various alarm mode. Line 4: the three alarm clocks with setting method or written "Snooze" with the display of the remaining time.

• Excellent precision, temperature compensated oscillator guaranteed DS32KHZ.

• Supported languages​​: Italian, English and German editable via button

• 3 independent alarms can be set: Once, Always, Week Mon-Fri, Week Mon-Sat with independent digital outputs for each clock alar, or only one digital output common to all alarm or buzzer.

• 10-minute snooze mode infinitely repeatable.

• Update daylight savings time / winter time settings automatically

• Storage and display up to 255 holidays and / or birthdays up to 3 events per day.

• Backlight brightness freely adjustable in 10 steps.

• B3V lithium battery backup for clock / calendar DS1306

• 9V battery backup for the system clock in the absence of the mains voltage, without backlight lcd and 1Hz led flashing at rate of 5 seconds.

• Timeout management buttons (see specifications)

Wiring diagram version 2.02 (21/07/2012)

This version implements the anti black-out and automatic daylight saving summer / winter. Some hints on the circuit anti black-out.
The purpose is to feed the clock correctly, inform the micro is in progress a blackout and have a backup battery that allows the clock to operate alarms in the event of a blackout.
We came to this conclusion:

12Vdc power supply is required, and because not all power supplies have a good filter, we have included C1 1000uF capacitor with its anti-transient from 0.1 uF better if disc (ceramic) or polyester.

The 7809 positive regulator, stabilizes the voltage to 9V, but because of the diode D1 this voltage rises to 9.5 ~ 9.7 V for two reasons, the first is used to operate the '"or" between D2 and D3, as in presence of the mains voltage, the voltage from D2 is higher than that from D3, according because it allows us to recharge the 9V battery.

For which the diodes D2 and D3 serve as switches to determine which power source will power the 7805. Output from 7805 was added an electrolytic capacitor 470uF 16V with his against transients, with the aim to have an excellent voltage (+5 V) well stabilized.

Diodes SB140 Vishay products are of the type Schottky, fast recovery and insertion loss of about 0.45 V ~ 0.7 V compared to 0.6 silicon diode like the 1N4004.

The recommended battery is produced by Ansmann and is 250 or 300mA / h, since the battery is connected to the circuit permanently, we set the charge current to approximately 10mA.

For which the value of Rx is 82 Ohm 1/2W

(Voltage on negative D4 - Voltage drop diode - Battery voltage) / Rx

(9,7V-0,45V-8,4V)/82 = 0,85/82 = 10mA

Finally, the signal from the positive part of DZ1 from 5.1 V serves to inform the micro that we have passed from the mains (inexhaustible) on backup battery power due to a power outage. To do this is connected the input of the micro RE1 to a 5.1 V zener diode (and its resistance to fall to 220 ohms) to the negative of the diode that protects the power supply network. The zener becomes necessary because the digital input does not support an input voltage higher than 5V.

During the blackout all the buttons are locked except PL1 and PL5 for the management of alarms and snooze.

At every second, while the micro performs other functions, is also tested for the presence of the supply voltage, if this is not present, we are in the process of black-out and operating in battery is necessary to limit the consumption, for which a flag goes from zero to one, it disables the PWM that drives the LCD backlight and LED syncro 1Hz instead of flashing every second, flashes every 5 seconds to indicate that we are in the process of blackouts. Many even in the absence of the LCD backlight reflect the characters so if you are in daylight or bright room you can read the time.

The flag above, if <> 0 means that we are being backed up, is incremented every second and is worth 5 when you turn on the LED 1Hz and is reset to 1 for a new cycle.

Upon the return of the mains voltage, the PWM is reactivated and the normal cycle.

Prototype supply anti black-out as the external clock is mounted on the PCB for version 2.0