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Monday, 20 October 2014

Easy Method to Reduce the Number of Decoded Outputs of 74HC4017 / 74HCT4017

by realfinetime  |  in Johnson Counter at  11:09

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          We have already seen the animated presentation of working of 74HC4017 / 74HCT4017 in previous blogs. As we know, 4017 is a 5 stage johnson counter with 10 decoded outputs as shown in the following circuit.


          In certain situations, we may not need all the 10 decoded outputs. For example, if we need only 7 decoded outputs, we have to eliminate 8th (Q7), 9th (Q8) and 10th (Q9) decoded outputs. One method is, simply disconnect the LEDs connected to these decoded outputs. This will not give the expected output because, the time delay between the blinking of 7th (Q6) LED and 1st (Q0) LED will become more. To avoid this problem, make some modifications in the circuit as shown below. Connect the decoded output, after the last LED to be blink, to the MR pin 4017. This will reset 4017 IC, when that decoded output  becomes HIGH. In this case Q7 pin of 4017 is connected to the MR pin of 4017.


          Similarly, if you want only 5 decoded outputs, make some simple modifications as shown in the following circuit.


Next : Video Demonstration of Working of 74HC4017 / 74HCT4017 >>>>

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