Hey everyone, I'm trying to create a countdown system, but I'm having trouble understanding how everything works together. I'm not really sure how to chain the parts properly. Could someone please show me a clear schematic or example of how to connect everything step by step?
Start with the clock circuit:
and connect the 1Hz output (top right) to the Clk input (middle left) of the 1's counter:
Then connect the CarryOut (lower right) to the Clk input (upper middle left) on the 10's counter:
The cascade connection between the two counters is shown here:
To add the preset option you need to insert the switches between the clock 1Hz output and the 1's counter, and the carry out of the 1's counter and the clock input of the 10's counter as shown here:
which disconnects it from automatic clock operation and allows you to clock it manually with the push buttons.
Note that the display digits are in the reverse order here. The 1's counter display is shown on the left on the schematic whereas in the physical world it will be positioned on the right.
like this?
BCD (binary coded decimal).
The JAM1-JAM4 pins set the value you want to reset the decade counter to, so in this case it has been set to the value of 0101 (5 decimal).
The reset is triggered by the combinational logic attached to the counter outputs Q1-Q4.
When ( Q2 AND Q3 are high ) OR when Q4 is HIGH the counter is reset.
The logic added will therefore reset the counter to 5 whenever the counter outputs a value of 6,7,8, or 9.
is this good?
You probably want the switches on all 6 counters so that you can set each individually.
You have too much reset logic. Only the 2nd, 4th (and potentially 5th and 6th) counter needs it.
The 1st counter (seconds units) drives the last digit so it needs to be able to count from 9 down to 0
The 2nd counter (seconds tens) drives the second last digit so needs to count from 5 down to 0 so needs the reset logic.
Same with the minutes counters.
What is the maximum number of hours are you wanting to count down from as that will affect the reset logic. No logic and it will count down from max of 99hours.
The same logic for the minutes and seconds and it will count down from max of 59hours.
but you could change the reset logic to make it from max of whatever you want.
