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 NXP Semiconductors

  • Gran Prix Starting Lights Circuit

  • Created: Nov 03, 2014

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Grand Prix starting lights are used in racing as indicators when a race is about to start. It is currently used by FISA for Formula One racing. The device can be used with slot car sets such as HO scale AFX/Life Like/Tyco sets and radio controlled cars. It uses a 74HC4024D IC which is a 7-stage binary ripple counter with a clock input (CP). Moreover, it has an overriding asynchronous master reset input (MR) and seven fully buffered parallel outputs (Q0 to Q6) featuring a low power dissipation.

The device uses 555 timer IC that is used as a clock pulse generator. Its output is fed via 1st and 2nd NAND gates of IC 4011 to 74HC4024D binary counter. The second gate of IC 4011 inverts the Q4 output of the binary counter (U1). Initially, U1 resets and all its outputs are low, including Q4, which causes the second gate of IC 4011 to present a logical high to the pin 8 input of the third gate which then passes pulses from the 555 clock circuit to the clock input of U1. The binary counter U1 will then begin counting.The four outputs of U1 are connected to a resistor 'ladder' which acts as a simple digital to analog converter (DAC). As the count increases, so does the voltage produced at the top of the ladder and this is connected to the inverting inputs of four comparators inside LM339 IC and to LM741,connected as a comparator. The positive inputs of the comparators are connected to the taps of a voltage divider, with the tapping voltages set using VR1, a 100k Ohms trimpot. As U1 counts, the rising stepped voltage from the DAC ladder switches the comparators on in sequence, starting with Igate 4 of LM339 and working up to LM741. As each comparator is turned on, its pair of LEDs is lit; first LEDs 1 & 2, then LEDs 3 & 4 and so on. When all five pairs of LEDs are lit, the next pulse from the timer moves the binary count to 10000, so the DAC voltage drops back to zero and all LEDs are off. At the same time, counting also stops, because the high state on Q4 causes the third gate of IC 40141 to block further gate pulses. Then, the circuit remains inactive until the counter is reset by pressing pushbutton switch S1. This allows a new sequence to begin.

This circuit can be applied to any type of racing such as drag racing, car racing, horse racing and many other racing tournaments. It has a starting light sequence similar to standard starting lights such as that in car racing games. This device is an effective indicator to start a good race.