10 OUTPUT LED SEQUENCER

Here is 10 output LED sequencer. After the last LED is illuminated, the circuit is reset. This circuit is build around readily available, low cost components - a 555 and decade counter CD4O1 7. The timer IC NE555 is wired as an astable multivibrator that produces 6Hz clock at its output pin 3. The 4017 is a CMOS decade counter with 10 outputs. Inputs include a CLOCK (Pin 1 4), a RESET (Pin 15), and a CLOCK INHIBIT (Pin 13). The clock input connects to a Schmitt trigger for pulse shaping and allows slow clock rise and fall times (not needed in our case). The counter advances one output at the rising edge of the clock signal if the CLOCK INHIBIT line is low. A high RESET signal resets the counter to the zero output. The circuit may be configured for counts less than 10 by connecting RESET to an output pin (one after the desired count). Thus, a five stage sequencer can be made by connecting pin 15 to pin 1. A CARRY-OUT signal (pin 12) can be used to clock subsequent stages in a multi-device counting chain. The output from 1C2 pin 3 is connected to clock pin (pin 14) of the IC3 for sequencing operations. NPN transistors Q1- Q10 are used to increase the output current for the LEDs which is set by the common 150 ohm resistor. In the circuit, only one of the outputs is HIGH at any one time and the output advances by one count with every clock pulse. But the circuit above is poorly designed. It does not need the voltage regulator as both chips can work up to 15v. The 4017 can supply 10mA to a LED on a 12v supply so that none of the transistors are needed. The circuit below shows the necessary components. The secret to designing a circuit is to look at the final design and ask: "is this component necessary?" Try removing a component and see if the circuit still works. Keep doing this with all the components. The circuit above was published in an Indian magazine with over 1,000,000 readers. The faults were obvious. How these faults passed an editorial committee is beyond me.  They are showing very poor design-leadership in allowing this oversight to be published. The faults are technical but are obvious to anyone who has constructed the circuit and experimented with it. Obviously the circuit has never been assembled with anyone with technical expertise.