Eight LED’s are used to indicate the pad currently selected. These LED’s are connected to a decade counter, which sequences the LED’s when it receives a clock pulse.Only one LED can be lit at a time from the decade counter, so although this circuit contains many LED’s only a small drain us placed on the battery. The clock pulse for the decade counter is generated by a 555 timer. Although wired as an a stable circuit, the 555 timer also has a push switch attached between pins 2 and 6. The pad selected will change each time the switch is pressed, although if the switch is held down the LED’s will quickly sequence, allowing you to change which pad unit you are using much quicker. The speed of this clock pulse can be changed by varying the 1K resistors on the 555 timer. Clock on the pad selecting decade counter is also connected to one of pins the output connector. This means that every time the counter in the controller advances, the counter in each pad unit does the same. That way you can have each pad unit wired to a certain output of the counter, and it will only listen to its correct signal. The countdown timer also works in a similar way although without the switch to advance the counter. On the countdown circuit the enable input of the counter is connected to output 7, making the sequence stop when it reaches the last LED. Output 7 is also wired to the launch line to fire the rocket when the count finishes. The launch select switch will either power the countdown circuit or the give power to the launch line directly when the launch switch is pressed, depending upon its position. LED’s are used to indicate launch….

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