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Build Your 4017 Decade Counter Sequence Circuit
Description
This circuit utilizes a CMOS 4017 decade counter to generate a series of four distinct occurrences. The number of occurrences within the sequence can be extended to nine or ten. Furthermore, the duration of each occurrence is independently adjustable. D13 induces the sequence to repeat continuously. If this component is omitted, the sequence will execute only once. A 12-volt supply is employed in this diagram, although the circuit operates effectively within a range of 5 to 15 volts.
The four outputs are sourced from pins 3, 2, 4 & 7, respectively. The current available from each output pin is regulated by R1, R2, R3 & R4. Each resistor provides sufficient current to drive a transistor switch. This switch can then be used to activate a relay, a buzzer, or similar devices.
It is possible to produce more intricate sequences, incorporating overlapping and repeating events. Additionally, you can determine the total number of times the sequence will repeat, alongside the specific point within the sequence where the repetition ceases.
Schematic Diagram
The individual occurrence lengths are controlled by the value of C5, and the values of R5, R6, R7 & R8, correspondingly. At the beginning of each occurrence, Q1 discharges C5. Subsequently, the relevant timing resistor takes control and charges C5 again. A 470uF capacitor was utilized in the prototype. With the resistor values depicted in the diagram, the events lasted approximately 38 seconds, 67 seconds, 49 seconds and 9 minutes, respectively. These times encompass an initial delay of approximately 14 seconds, occurring while Q1 discharges C5. Until Q1 switches off, the timing resistors cannot initiate the charging of C5.
Manufacturing variances can cause results to differ from those obtained by the author. However, consistently utilizing the same capacitor to activate the same input pin ensures that the length of each step in the sequence is relatively predictable. A single reliable practical observation is sufficient to allow you to calculate the remaining parameters.
The author observed roughly 12 seconds for every 100k/100uF combination. Therefore, a 1M resistor combined with a 100uF capacitor will produce approximately 120 seconds, or two minutes. This must be added to the initial 14 seconds, while Q1 discharges C5. To shorten this discharge time, reduce the value of R11.
There is no theoretical limit to the size of C5. With a 470uF capacitor and a 1M resistor, the author obtained just under 9 minutes. Consequently, with a 4700uF capacitor and a 1M resistor, the author should achieve just under 90 minutes. If the resistor is increased to 4M7, the output duration should approach approximately 7 hours.
Veroboard Layout
Part list
