28 LED Clock Timers


Posted on Feb 5, 2014

This is 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 Timers
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

    200mW High Quality FM Transmitter With TX-200
    testing troubleshooting inverter
    simple circuit mini bicycle bel
    catalinbread super charged overdrive
    clk3 binary alarm clock
    Ding-Dong sound generator
    digital clock pic microcontroller ds1307
    RA-203
    DC-coupled multi-stage amplifier circuit b
    AR-300 DC arc welding machine circuit



    Top