games timer 2

Posted on Feb 4, 2014

Circuits using large value resistor/capacitor combinations are not very accurate because of the wide tolerance and leakage current of polarised capacitors. A better solution is to use an astable circuit together with a binary counter/divider chain which reduces the frequency of the astable pulses. The 4060 cmos integrated circuit is ideal for the games timer application. In this

games timer 2
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session, you will investigate how to set up the counter/display subsystem of the games timer using another cmos integrated circuit, the 4017 decade counter. To find out about the 4017, you need a source of pulses. You could use the 4060 astable circuit investigated in the previous session, but it is more convenient to build a temporary alternative circuit. About the easiest way of building an astable is using a special type of NAND gate, called a Schmitt trigger NAND gate. Here are the symbols for normal and Schmitt trigger gates: The Schmitt trigger gate has two different thresholds. If the voltage applied to one of the inputs to the gate starts at 0V and is slowly increased, the logic 1 threshold, when the input starts to count as a HIGH voltage, is around two-thirds of the power supply voltage, that is, about 6V with a 9V supply. On the other hand, if the voltage connected to the input starts at 9V and is slowly decreased, the logic 0 threshold, when the input counts as a LOW voltage, is around one-third of the power supply voltage, or about 3V. This difference in thresholds allows you to use a Schmitt trigger gate as the basis for an extremely simple astable circuit. The 4017 is a divide-by-10, or decade counter, with 10 individual outputs which go HIGH in turn when pulses are fed to its CLOCK input. The connection details for the 4017 are: To make the 4017 work, you need to connect the power supply pins (`beasties`...

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