Chapter 6 Electromechan e r m m c a a ni cal a S Sy s st ems e s 163 Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. 5. Turn on the power source and count the number of timing cycles needed to energize the 7490 LED readout. What mathematical function does this represent? 6. Turn off the power source and move the LED readout of the 7490 to output A. Turn on the power again and determine the counting cycles needed to energize the LED. What mathematical function does this represent? 7. Turn off the power supply and alter the SN7490 circuitry. Change C1 of the time base generator to 4 μF. 8. Turn on the power supply and open the reset switch. Close the switch during a time when the time base generator LED is off. Count the number of timing cycles needed to energize the SN7490 LED. Also, count the number of timing cycles needed to turn off the LED. What does this represent as an output of the IC? Analysis 1. How could the digital timer of this experiment be extended? Name two ways. 2. How can the digital timer of this experiment be made variable? 3. Would it be advantageous to have a reset switch on an actual digital timer? Why? +VCC SN7490 Counter 14 1 13 2 12 3 11 4 10 5 9 6 8 7 390 Ω To pin 3 of clock source Reset switch LED Goodheart-Willcox Publisher Modifi counter circuit. fied