EGR 450 Manufacturing Controls Project


Posted on Feb 6, 2014

A timing and counting circuit using integrated circuit chips with seven-segment LED displays is used to display current lap time, the previous lap time, and also the total number of laps completed on an assembled 1/64th-scale slot car racetrack. A switch contacted by the car will increment the lap counter, reset the lap timer, and also update the


EGR 450 Manufacturing Controls Project
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prior lap ’s time. Two other switches will also be used, one to turn the power on and off, and another to reset the total number of laps completed. This circuit was built using the BCD 0-99 Counter in the Engineer ’s Mini-Notebook on Digital Logic Circuits by Forrest Mims III, available from Radio Shack. This circuit serves as the output driver for the LED ’s used to display the timer and counter circuit outputs. The schematic for this circuit is shown below as Figure 1. A 555 IC Timer was used to create the oscillating pulse for the input to the display circuit shown in Figure 1. The output pulse from pin 3 of the timer is wired to pin 14 of the 74LS90 chip in the counter. This circuit was also connected to two more identical circuits showing three digits. This circuit will be used to measure the time to complete a lap on the track ranging from 0. 1 seconds to 99. 9 seconds. The schematic for the timer circuit is shown below as Figure 3. Using the timer above with the shown values, the timing circuit oscillates at 0. 1 Hz giving us a timing display accurate to 0. 1 seconds. For a slower timer, the capacitance needs to be increased. To speed up the timer, the capacitance values need to be lowered. However, a faster timer will be harder to calibrate for accuracy. A flip-flop circuit was used to display the just completed lap ’s time. A 74175 IC inserted between the 74LS90 and 74LS47 IC ’s causes the display to only show the...




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