Written by Amol Shah, on May-2008

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CYCLIC TIMER is a device whose output turns ON-OFF continuously in a cyclic manner at predetermined interval. The duration for which the device is to be turned ON/OFF can be varied with the help of keypad & a memory is used to save this duration. So even if there is a power failure the ON/OFF duration is saved in the EEPROM. The duration can be set from 1seconds to 9999seconds or from 1min to 9999mins.

Our device consists of the following section

1.       Microcontroller.

2.       Keypad.

3.       Display.

4.       Memory.

5.       Relay.

6.       Power Supply.

ATMEL’s AT89S5I microcontroller is used.  When POWER is turned ON the controller first gets the ON/OFF duration from the EEPROM. Then it TURNS ON the output for the ON duration then TURNS OFF the output for OFF duration. This process goes on continuously. It also polls for the keypad & displays the duration on the Display.

The keypad section consists of 4 keys i.e. Mode, Increment, Decrement and Exit. Using these four keys we can change the ON/OFF duration.

Display used is a 4-digit, Common Anode, multiplexed 7-segment display. That means that the LED’s in the same segment share a common Anode. The cathodes of all the four displays are connected together to form a matrix. We will be using Multiplexing technique i.e. only one digit is being displayed at a time & each digit is ON for only a short period of time. This process being faster than the human eye to distinguish so it looks like the display is continuously ON. This effect is called persistence of vision.

An EEPROM is used to store the ON/OFF duration. So even if there is power failure the durations are saved in EEPROM.

A relay is used to turn ON/OFF any external device. The relay that we are using can be used to TURN ON/OFF loads of 5 Amperes. Tutorial for INTERFACING RELAY TO MICROCONTROLLER.

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