24 Second Shot Clock
This is a countdown timer circuit starting from 24 similar to the basketball shot clock. It will count from 24 down to 0 every second.
Assembly Instruction:
We will use the 74LS191 IC to create the countdown timer. We will create a 2-stage counter using the said IC. The output will be connected to a 74LS47 IC to display the time. A 555 timer circuit will be used as the clock for the 74LS191 IC. The shot clock circuit would be:
The first 74LS191 IC would be for the ones digit. A clock producing a pulse of 1 second will be connected to the clock leg of the first IC. The BO leg of the first would be connected to the down leg of the second 74LS191 IC. This serves as the clock pulse of the second. In order for the circuit to stop when the time reaches 00, connect the first BO to an AND gate and the second BO would be negated and connected to the same AND gate. The output of the AND would be connected to both clear legs. Doing so will stop the shot clock during 00 time. A push-button can be used as switches for the Start/Reset and Pause button. Grounding the load of both the 74LS191 IC would display the preset values on the IC which in this case is 24. Providing a voltage to the load will start the counting. The pause would be to disconnect the clock using a switch to stop the counting.
*Note: For the circuit to properly operate, connect all legs to their proper connections. As much as possible, do not leave any hanging inputs. For example, to display an output of "2", we should provide an input of 0, 0, 1 and 0 to legs D, C, B and A respectively. For an input of 0, do not leave it hanging and connect it to ground.
*Note: For the circuit to properly operate, connect all legs to their proper connections. As much as possible, do not leave any hanging inputs. For example, to display an output of "2", we should provide an input of 0, 0, 1 and 0 to legs D, C, B and A respectively. For an input of 0, do not leave it hanging and connect it to ground.
Pictorials:
