Home Electronics Prize LEDs
	Electronics - Prize LEDs This circuit is used for controlling the nine prize select LEDs at the bottom of the Plinko board. The design is similar to the circuit used for the countdown timer, however since there are nine LEDs instead of eight, an extra shift register is required to control all the LEDs. The eighth output of the first shift register is connected to the A input of the second shift register and plays the role of data input. Both shift registers share the same clock input. Since the shift register logically ands the data inputs A and B, input B is tied high. The reset input is also tied high since a low input resets the shift register. With this configuration, the data input (A) bit will be shifted into the Q outputs each time the clock is pulsed. If A is high, the LED will light, if A is low the LED will not light. Any pattern of the nine LEDs can be created by shifting in lit and unlit LEDs. The output of the shift register connects to the gate of a 2N7000 MOSFET. When sufficient voltage is applied, the MOSFET saturates and current flows through it to light the LEDs. The yellow LEDs used had a forward voltage drop of 1.9V and the 2N7000 MOSFET has an RDS value of 5.3Ω. Based on these values, 200Ω resistors were chosen to provide the LEDs with a 16mA current when the MOSFET is saturated.