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HowTo: A low cost lighting sequencer (Pt 1)
( Roger Otis)
Step 3 : The Decade Counter
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| | CD4017 is a decade counter. As shown, the counter counts from 0 to 9 and resets to start the count again. Each pulse advances the counter with a corresponding “high” at outputs Q0 to Q9. I use optoisolator ICs to drive triacs. Only one output channel is shown. The optoisolator circuit is very similar to some of the other SSR circuits shown on this website.
In the most basic form, the transistor shown at output Q0 of the decade counter is really not needed. The decade counter can drive the LED in the optoisolator directly with the proper size of current limiting resistor. The 100K resistor, the 1K resistor and transistor can be replaced with a 1K resistor from pin 3 in series with the LED in MOC3010. The resistors and transistor are very useful for modifications which will be shown later and for the ability to add a display to check operation.
The 555 timer and CD4017 have wide operating voltage ranges. I use a plug-in wall adapter with a 9 volt DC output as a power supply. The voltage is unregulated. It is a good idea to place a 25 to 50 microfarad capacitor from V+ to ground. Neglecting the voltage drop across the transistor and LED in the optoisolator, the current through the LED is 9 volts/1000 ohms or about 9 MA.
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