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The 4017 integrated circuit (IC) has 10 outputs. In its most basic circuit, the 0 output starts off being high while the rest of the outputs are held low. With each high pulse to the clock pin, the next higher number output is high, while the rest are all low.
I demonstrated the diagram above in the video below. LED connected to output 0 lights up when power is applied. That is because output 0 is high (close to the positive supply voltage). The 555 timer output is connected to the clock input (pin 14) of the 4017. With each high pulse, the next higher up 4017 output number goes high, while the one that was high at the time, goes low. If output 9 is high when the clock pin (14) gets a high pulse, then it goes low and output 0 goes high again.
- Reset pin (15) is usually held low so that it doesn’t do anything. A high signal to the reset pin sets output 0 high, and the rest of the outputs low.
- Enable pin (13) is held low so that the outputs can cycle the high output with each high input to the clock. A high input to the enable pin, holds the output high that was already high. Each high pulse to the clock pin (14) is ignored by the outputs while the enable pin is high.
- Each outputs can provide about 10mA of current. That’s why I used blue LEDs, which are pretty bright at low current, instead of red LEDs which need to have closer to 15mA of current to be bright.
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