sequential timer


Posted on Feb 6, 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. You`re not limited to a series of - `one after the other` - events. You can produce More Complex Sequences - with overlapping and


sequential timer
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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 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. 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 sequence should be fairly predictable. All you need is one reliable practical observation. Then you can calculate the rest. I got roughly 12 seconds for every 100k/100uF combination. So a 1M resistor and a 100uF...




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