This project can be used to understand and develop an application of ic 555 timer. The project can be used for a quiz with up to 5 contestants (or teams). Each of the contestant have a trigger push-switch in his/her hand. And an LED is fitted on the table. When a trigger switch is pressed the corresponding LED lights , sounds the bleeper and it keeps other trigger switches away from triggering or working. So this shows which contestant was the first to press the switch. A reset push switch which is operated by quiz master, is used to cancel the bleeper and switches of the LED so that the next question may b asked and the switches can be operated again.
See the circuit diagram. It consists of four ic 555 timer operated in bistable mode( stable in both high and low outputs) which are triggered or reset when their inputs are low. The reset input of all the ic 555 is joined together and operated by a single reset push-switch. The trigger switches are connected to the bistable trigger( pin2) through a 0.1 uF capacitor so that only the initial press triggers the bistable; and continying to hold the switch closed will have no effect. Now the switch is directly connected to the bistables. This prevents the quizmaster from resetting the circcuit until the trigger swicth was released. As it has been observed that some contestants hold the switch until they are asked to give their answer. When a trigger switch triggers a bistable output (pin 3) lights an LED and makes the trigger line 'high', this prevents any other bistable being triggered and sounds the bleeper. We have used a diode to link the output to the trigger line.
See the circuit diagram. It consists of four ic 555 timer operated in bistable mode( stable in both high and low outputs) which are triggered or reset when their inputs are low. The reset input of all the ic 555 is joined together and operated by a single reset push-switch. The trigger switches are connected to the bistable trigger( pin2) through a 0.1 uF capacitor so that only the initial press triggers the bistable; and continying to hold the switch closed will have no effect. Now the switch is directly connected to the bistables. This prevents the quizmaster from resetting the circcuit until the trigger swicth was released. As it has been observed that some contestants hold the switch until they are asked to give their answer. When a trigger switch triggers a bistable output (pin 3) lights an LED and makes the trigger line 'high', this prevents any other bistable being triggered and sounds the bleeper. We have used a diode to link the output to the trigger line.
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