28 LED Clock Timer Circuit


Posted on Feb 6, 2014

a programmable clock timer circuit that uses individual LEDs to indicate hours and minutes. 12 LEDs can be arranged in a circle to represent the 12 hours of a clock face and an additional 12 LEDs can be arranged in an outer circle to indicate 5 minute intervals within the hour. 4 additional LEDs are used to indicate 1 to 4 minutes of time


28 LED Clock Timer Circuit
Click here to download the full size of the above Circuit.

within each 5 minute interval. The circuit is powered from a small 12. 6 volt center tapped line transformer and the 60 cycle line frequency is used for the time base. The transformer is connected in a full wave, center tapped configuration which produces about 8. 5 volts unregulated DC. A 47 ohm resistor and 5. 1 volt, 1 watt zener regulate the supply for the 74HCT circuits. A 14 stage 74HCT4020 binary counter and two NAND gates are used to divide the line frequency by 3600 producing a one minute pulse which is used to reset the counter and advance the 4017 decade counter. The decade counter counts the minutes from 0 to 4 and resets on the fifth count or every 5 minutes which advances one section of a dual 4 bit binary counter (74HCT393). The 4 bits of this counter are then decoded into one of 12 outputs by two 74HCT138 (3 line to 8 line) decoder circuits. The most significant bit is used in conjunction with an inverter to select the appropriate decoder. During the first eight counts, the low state of the MSB is inverted to supply a high level to enable the decoder that drives the first 8 LEDs. During counts 9 to 12, the MSB will be high and will select the decoder that drives the remaining 4 LEDs while disabling the other decoder. The decoded outputs are low when selected and the 12 LEDs are connected common anode with a 330 ohm current limiting resistor to the +5 volt supply. The 5th output of the second decoder (pin 11)...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Video title generator
    Solar Garden LED Lighting
    Simple field strength meter
    AVR Serial Port Programmer
    MS6714 4 Stereo Inputs And 1 Stereo Output Volume Tone Balance Loudness And Selectable Input Gain
    A Unipolar Stepper Motor Drive Using The Z8 Encore! ?® Mcu
    58mhz jammer
    yamaha dspa 1 processor
    InfiniBand Bus Description
    Bi-Level Squelch
    Automatically Repeating Interval-Timer Circuit



    Top