28 led clock timer with 74hct circuit

This is a programmable alarm timer ambit that uses alone LEDs to announce hours and minutes. 12 LEDs can be abiding in a amphitheater to represent the 12 hours of a alarm face and an added 12 LEDs can be abiding in an alien amphitheater to announce 5 minute intervals aural the hour. 4 added LEDs are acclimated to announce 1 to 4 account of time au
28 led clock timer with 74hct circuit - schematic

ral anniversary 5 minute interval. The ambit is powered from a baby 12. 6 volt centermost broke band agent and the 60 aeon band abundance is acclimated for the time base. The agent is affiliated in a abounding wave, centermost broke agreement which produces about 8. 5 volts able DC. A 47 ohm resistor and 5. 1 volt, 1 watt zener adapt the accumulation for the 74HCT circuits. A 14 date 74HCT4020 bifold adverse and two NAND gates are acclimated to bisect the band abundance by 3600 bearing a one minute beating which is acclimated to displace the adverse and beforehand the 4017 decade counter. The decade adverse counts the account from 0 to 4 and resets on the fifth calculation or every 5 account which advances one area of a bifold 4 bit bifold adverse (74HCT393). The 4 $. 25 of this adverse are again decoded into one of 12 outputs by two 74HCT138 (3 band to 8 line) decoder circuits. The best cogent bit is acclimated in affiliation with an inverter to baddest the adapted decoder. During the aboriginal eight counts, the low accompaniment of the MSB is astern to accumulation a aerial akin to accredit the decoder that drives the aboriginal 8 LEDs. During counts 9 to 12, the MSB will be aerial and will baddest the decoder that drives the actual 4 LEDs while disabling the added decoder. The decoded outputs are low back called and the 12 LEDs are affiliated accepted anode with a 330 ohm accepted attached resistor to the +5 volt...

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