i have been assigned to design a digital alarm clock operating 24 hour time format and giving output in 7 LED digit set, input clock pulse operates minutes
no assembly language , just designing circuit using logical gates , decoders , mux , flipflops and other stuff ….
kindly anyone could guide me a small , i have no thought
First you need a "timebase" which is a stable clock pulse generator. They are usually based on a high frequency crystal oscillator which has it’s output frequency divided with various counter and divider chips. (74ls92, 74ls93, 4017, 4040, etc…) down to the desired frequency. The desired frequency depends on the precision you intend to show. To show seconds you would want a 1 Hz timebase. To show only minutes and hours you need a 1/60th Hz timebase. If you want to show milliseconds you need to have a 1KHz timebase. For the rest of this answer I will describe a clock that displays hours, minutes and seconds. A 1 Hz clock is applied to the clock input of the first of six BCD (binary coded decimal) counter IC’s, each connected through show decoders and current limiting resistors to seven segment LED displays. The six counter/show circuits are arranged as three pairs of two digit counters. The right most counter in each pair counts incoming clock pulses on its clock input and is cascaded to the counter on its left. This means that the carry output of the right (ones place) counter is connected to the clock input of the left (tens place)counter. When the ones counter overflows (reaches a count of ten) it resets to zero and a pulse on the carry output increments the tens counter. With the 1 Hz timebase applied to the first two digit counter it will increment the show at 1 Hz but we have a problem As is this circuit will show a count of 0 through 99 before reseting. You want 99 seconds to be showed as 1 minute 39 seconds.You need a way to decode when the count reaches 60 to reset the "seconds" counters to zero.The BCD outputs from the tens counter connected to the inputs of a 4 input NAND gate (with inverters in series with outputs A and D) can be used to detect the binary code for 6 and the NAND gates output can be used not only to reset the seconds counters to 0 but it happens to be a convienient 1/60 Hz clock source for the minutes counter. The minutes counter is reset and the hour counter is incremented exactly the same way. The reset circuit for the hours counter will be a bit more complex as the output data on the tens place counter is not enough to decode the reset point. So an 8 input nand connected to all eight outputs from the hours counters (through inverters as required) will be needed to decode binary coded decimal 25 to reset the hours count to zero. To implement an alarm function you could use BCD coded thumbweel switches (or direct entry in binary with dip switches) to apply the binary representation of the alarm time to the inputs of digital comparator IC’s. Digital comparators turn on their outputs when the data words on their inputs are identical. The comparators will compare the alarm set switch data with the data present on the counter outputs (just the hour and minute counters to make it simpler) and when the alarm time is reached the comparators outputs will all change state and then AND gated together, would in turn latch a relay and turn on the alarm. Note: While this all should work in theory I haven’t built this circuit so it may need modification. Also, there may be more efficient designs but what do you want for free?
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First you need a "timebase" which is a stable clock pulse generator. They are usually based on a high frequency crystal oscillator which has it’s output frequency divided with various counter and divider chips. (74ls92, 74ls93, 4017, 4040, etc…) down to the desired frequency. The desired frequency depends on the precision you intend to show. To show seconds you would want a 1 Hz timebase. To show only minutes and hours you need a 1/60th Hz timebase. If you want to show milliseconds you need to have a 1KHz timebase. For the rest of this answer I will describe a clock that displays hours, minutes and seconds. A 1 Hz clock is applied to the clock input of the first of six BCD (binary coded decimal) counter IC’s, each connected through show decoders and current limiting resistors to seven segment LED displays. The six counter/show circuits are arranged as three pairs of two digit counters. The right most counter in each pair counts incoming clock pulses on its clock input and is cascaded to the counter on its left. This means that the carry output of the right (ones place) counter is connected to the clock input of the left (tens place)counter. When the ones counter overflows (reaches a count of ten) it resets to zero and a pulse on the carry output increments the tens counter. With the 1 Hz timebase applied to the first two digit counter it will increment the show at 1 Hz but we have a problem As is this circuit will show a count of 0 through 99 before reseting. You want 99 seconds to be showed as 1 minute 39 seconds.You need a way to decode when the count reaches 60 to reset the "seconds" counters to zero.The BCD outputs from the tens counter connected to the inputs of a 4 input NAND gate (with inverters in series with outputs A and D) can be used to detect the binary code for 6 and the NAND gates output can be used not only to reset the seconds counters to 0 but it happens to be a convienient 1/60 Hz clock source for the minutes counter. The minutes counter is reset and the hour counter is incremented exactly the same way. The reset circuit for the hours counter will be a bit more complex as the output data on the tens place counter is not enough to decode the reset point. So an 8 input nand connected to all eight outputs from the hours counters (through inverters as required) will be needed to decode binary coded decimal 25 to reset the hours count to zero. To implement an alarm function you could use BCD coded thumbweel switches (or direct entry in binary with dip switches) to apply the binary representation of the alarm time to the inputs of digital comparator IC’s. Digital comparators turn on their outputs when the data words on their inputs are identical. The comparators will compare the alarm set switch data with the data present on the counter outputs (just the hour and minute counters to make it simpler) and when the alarm time is reached the comparators outputs will all change state and then AND gated together, would in turn latch a relay and turn on the alarm. Note: While this all should work in theory I haven’t built this circuit so it may need modification. Also, there may be more efficient designs but what do you want for free?
References :
Many years as an electronics hobbyist.