How To Build A Sequential Timer Using A Cmos 4017

Posted on Feb 5, 2014

This circuit uses a Cmos 4017 decade counter to create a sequence of four separate events. The number of events in the sequence may be increased to nine or ten. And the length of each event is controlled independently. D13 causes the sequence to repeat continuously. If you leave out D13 - the sequence will run only once. I`ve used a 12-volt supply

How To Build A Sequential Timer Using A Cmos 4017
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in the diagram - but the circuit will work at anything from 5 to 15-volts. The four outputs are taken from pins 3, 2, 4 & 7 - in that order. The current available from each output pin is controlled by R1, R2, R3 & R4. Each resistor will supply more than enough current to operate a transistor switch. And the switch can be used to energize a relay - sound a buzzer etc. You`re not limited to a series of - "one after the other" - events. You can produce More Complex Sequences - with overlapping and repeating events. You can also fix the total number of times your sequence will repeat - as well as the point in the sequence where the repetition will stop. The individual output times are controlled by the value of C5 - and the values of R5, R6, R7 & R8 respectively. At the beginning of each event - Q1 discharges C5. Then the relevant timing resistor takes over - and charges C5 up again. I used a 470uF capacitor in the prototype. And with the resistor values shown in the diagram - the events lasted 38 seconds, 67 seconds, 49 seconds and 9 minutes - respectively. These times each include an initial delay of about 14 seconds - while Q1 discharges C5. Until Q1 switches off - the timing resistors cannot begin to charge C5. Manufacturing tolerances mean that your results are likely to be different from mine. However - because you`re always using the same capacitor to activate the same input pin - the length of each step in your...

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