LED sequencer with oscillator
Created: Feb 11, 2014
No description available.
A LED sequencer is a circuit containing LEDs for visual presentation purposes. It comprises a list of components particularly LEDs and a decade counter allowing it to operate. Meanwhile, a decade counter is one that counts in decimal digits, rather than binary. A decade counter may have each digit binary encoded or other binary encodings.
The 74HC4017 is a five-stage Johnson decade counter with 10 decoded outputs (Q0 to Q9), an output from the most significant flip-flop (Q5-9), two clock inputs (CP0 and CP1) and an overriding synchronous master reset input (MR). The counter is advanced by either a LOW-to-HIGH transition at CP0 while CP1 is LOW or a HIGH-to-LOW transition at CP1 while CP0 is HIGH. When cascading counters, the Q5-9 output, which is LOW while the counter is in states 5, 6, 7, 8 and 9, can be used to drive the CP0 input of the next counter. A HIGH on MR resets the counter to zero (Q0 = Q5-9 = HIGH; Q1 to Q9 = LOW) independent of the clock inputs (CP0 and CP1). An internal circuit provides automatic code correction of the counter; following any illegal codes the counter returns to a proper counting mode within 11 clock pulses. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of VCC.
The 74HC4017 has 10 output terminals. One of these ten terminals will be in a "high" state at any given time, with all others being "low," giving a "one-of-ten" output sequence. If low-to-high voltage pulses are applied to the "clock" terminal of the IC, it will increment its count, forcing the next output into a "high" state. With a 555 timer connected as an astable multivibrator (oscillator) of low frequency, the IC will cycle through its ten-count sequence, lighting up each LED, one at a time, and "recycling" back to the first LED. The result is a visually pleasing sequence of flashing lights.