the first decade counter cd 4017 and divides it again by 10 in the second decade counter cd 4017 by anding the two outputs from each of the divider stages the output will be a 1 duty cycle pulse in other words out of every 100 ms period there is a 1 ms pulse when the switch block 220 is open calibrate position the output to block 240 will be u201c 0 u201d 0 volt and the output from block 240 to block 250 will be u201c 1 u201d 12 volt all the time when the switch in block 220 is closed the output from block 220 will be u201c 1 u201d and the led will be turned on the output of block 240 will be a pulse train that has a duty cycle of 1 this means the output will be u201c 0 u201d 0 volt 99 of the time and u201c 1 u201d 12 volt for 1 of the time this pulse train goes to block 250 into a 2 k resistor and 0 1 uf capacitor an rc circuit in one branch and straight through without encountering any circuit components in a second branch the rc circuit slightly delays the original signal while the second branch allows the original signal to travel through unimpeded and without any delay fig2 b shows how the original signal and the delayed signal fed to an and gate generate a pulse that is slightly narrower than the original signal this is because the output of the and gate will only.