Tag Archive: Variable


  The following CD4017 circuits have not been tested and is presented here as a possibility only. If you experiment with this circuit, please send me any problems found so that the circuit can be updated.

  The following circuits are designed to change the duration of each positive output pulse from the astable timer. The circuits use a CD4017 Decade Counter / Decoder to provide nine or ten steps in the cycle.

  The first circuit operates with a repeating ten step cycle. Each output pulse is longer than the previous until a count of ten is reached at which time the cycle will repeat.

  The second circuit has a nine step cycle that stops at the end of the cycle. The cycle is restarted or reset when the RESET input is briefly made high.

  The CD4017 can be configured to give count lengths between 1 and 10. Refer to the timing diagram in the CD4017 data sheet for a better understanding of the IC’s operation.


Parts List:

R1,R6,R11 = 10K

R2,R9 = 1K8

R3 = 100 ohm

R4,R8 = 1K

R5 = 22K

R7 = 1M

*R10 = 0.003 ohm

R12 = 3K9

R13 = 100K

R14 = 10 ohm/1 Watt

P1 = 20K (Frequency adjust)

P2 = 10K (Duty Cycle)

P3 = 1K (Current Limiting)

C1 = 1000uF, 64V

C2 = 10nF, polyester

C3 = 100uF, 64V

C4 = 22nF

C5 = 47uF, 35V

D1,D2 = 1N4004

U1 = LM7810, volt regulator

U2 = LM324, Op-amp

Q1 = IRFP064N, IRFZ44, etc. MOSFet