quiz selector

In a `professional` quiz, some form of electronic detector is invariably used to determine which can- didate is first to indicate that he thinks he knows the answer. The circuit shown here can be used to do the same job. Push-button SS is under control of the quiz master. As long as he keeps this button depressed, none of the indi- cation circuits will work. As soon as he releases it, the other circuits become operative. The first candidate to push his button ( S l -S4) triggers the associated monostable (IC1-IC4). The monostable turns on an indicator LED and simul- taneously blocks the other three mono- stables via N 1.