Posted on Mar 18, 2013

The circuit consists of two building blocks. The first is a square wave oscillator made up of two transistors in a multivibrator arrangement and the second is a CD 4017 decade counter IC. The multivibrator contains two extra components to speed up the waveform and make it acceptable for all brands of 4017`s. Unless the output has a very fast rise and fall characteristic, some 4017`s fail to operate properly. They either do not work at all or jump two or three outputs, losing the scanning effect.

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The two speed-up components are the signal diode and 39k resistor and are essential for reliable operation. The output of the multivibrator feeds into the CLOCK INPUT of the chip. From there is goes to a complex counting circuit inside the 4017. The circ

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