Sunday, March 3, 2013

DS1307 Real Time Seven Segment Clock Circuit - 16F88

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DS1307 IC
DS1307 is a low power serial real time clock with full binary coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM (Non Volatile Static Random Access Memory). Data and Address are transferred serially through a bidirectional I2C bus.

The RTC provides year, month, date, hour, minute and second information. The end date of months is automatically adjusted for months fewer than 31 days including leap year compensation up to year 2100. It can operate either in 24-hour format or 12-hour format with AM/PM indicator.

DS1307 comes with built-in power sensing circuit which senses power failures and automatically switches to back up supply. We can provide a 3V CMOS Battery for that. The DS1307 RTC uses an external 32.768 kHz Crystal Oscillator and it does not requires any external resistors or capacitors to operate.

DS1307 Block Diagram
DS1307 Block Diagram

In this project, I used ds1307 as real time clock ic and PIC16f88 as micro-controller. To save micro-controller pins there are four input keys which are all connected to a single analogue input pin. This pin also drives one of the seven segment display LEDs so it has to be switched between input (to read the analogue voltage) and output (to drive the led). Each key pulls the analogue input to a different voltage level which you can easily read using the ADC (RA0).

DS1307 Real Time Clock circuit
Circuit Diagram

Set Time

Mode : Pressing mode button cycles the display showing 3 different data.

Mode 1 : Time only
Mode 2 : Seconds only
Mode 3 : Stand-by


Set : To change the value, set button must be pressed.

Set 1 :  Edit mode, show Minute
Set 2 :  Edit mode, show Hour
Set 3 :  Return to clock mode


Up and Down : After Pressing set button, you can change the values indicated on clock by using this buttons.

UP :  Values ++
In clock mode it will also change the 12/24Hr format.

Down :  Values --
In clock mode it will do nothing.

Clock Accuracy:

The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional error will be added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the oscillator circuit may result in the clock running fast.

To ensure the crystal oscillates correctly you must ensure that;
  • Crystal uses 12.7pf load capacitance (correct crystal type).
  • The crystal is close to the IC.
  • The tracks are short.
  • The chip supply has lots of decoupling (capacitors from +5V to GND). e.g. A 100n and a 10n
  • There are no signal tracks near to the crystal.
  • For a PCB: It has a guard ring and a ground plane and away from digital signals.

DS1307 Datasheet
PIC16F88 Datasheet

PIC16F88 pin
Pin Connection


I Used mikroC for compile this project.
Also you can get PCF8583 version from here.

Saturday, March 2, 2013

PCF8583 Real Time Seven Segment Clock Circuit - 16F88

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Basic Connection of PCF8583
Basic Connection of PCF8583
The PCF8583 is a clock and calendar chip based on a 2048 bit static CMOS RAM organized as 256words by 8 bits. Addresses and data are transferred serially via the two-line bidirectional I2C-bus.

The built-in word address register is incremented automatically after each written or read data byte. Address pin A0 is used for programming the hardware address, allowing the connection of two devices to the bus without additional hardware.

The built-in 32.768 kHz oscillator circuit and the first 8 bytes of the RAM are used for the clock, calendar, and counter functions. The next 8 bytes can be programmed as alarm registers or used as free RAM space. The remaining 240 bytes are free RAM locations.

Block diagram of PCF8583
Block diagram of PCF8583

Features:

  • I2C-bus interface operating supply voltage: 2.5 V to 6 V
  • Clock operating supply voltage 1.0 V to 6.0 V at 0 °C to +70 °C
  • 240 × 8-bit low-voltage RAM
  • Data retention voltage: 1.0 V to 6.0 V
  • Operating current (at fSCL = 0 Hz): max 50 μA
  • Clock function with four year calendar
  • Universal timer with alarm and overflow indication
  • 24 hour or 12 hour format
  • 32.768 kHz or 50 Hz time base
  • Serial input and output bus (I2C-bus)
  • Automatic word address incrementing
  • Programmable alarm, timer, and interrupt function
  • Slave addresses: A1h or A3h for reading, A0h or A2h for writing

PCF8583 Real Time Clock circuit
Circuit Diagram

This clock circuit is same as DS1307 - Real Time Clock. The only different is here I used PCF8583 RTC clock ic and change firmware. Because registers of DS1307 and PCF8583 are different.

To save micro-controller pins there are four input keys which are all connected to a single analogue input pin. This pin also drives one of the seven segment display LEDs so it has to be switched between input (to read the analogue voltage) and output (to drive the led). Each key pulls the analogue input to a different voltage level which you can easily read using the ADC (RA0).


Set Time:

Mode : Pressing mode button cycles the display showing 3 different data.

Mode 1 : Time only
Mode 2 : Seconds only
Mode 3 : Stand-by


Set : To change the value, set button must be pressed.

Set 1 :  Edit mode, show Minute
Set 2 :  Edit mode, show Hour
Set 3 :  Return to clock mode


Up and Down : After Pressing set button, you can change the values indicated on clock by using this buttons.

UP :  Values ++
In clock mode it will also change the 12/24Hr format.

Down :  Values --
In clock mode it will do nothing.

Quartz Frequency Adjustment:

By evaluating the average capacitance necessary for the application layout, a fixed capacitor can be used. The frequency is measured using the 1Hz signal available after power-on at the interrupt output (pin 7). The frequency tolerance depends on the quartz crystal tolerance, the capacitor tolerance and the device-to-device tolerance. Average deviations of 5 minutes per year are possible. See data sheet for more detail.

Use mikroC for compile.

PCF8583 Datasheet

PIC16F88 Datasheet

PIC16F88 pin
PIC16F88 Pin Connection

 

on line

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