555 Oscillator and Decade Counter - doc00020
This is a demo of the standard LED running lights
that many know of, the only thing different is that
you can try out the project on this page by a
The 555 clocks 4017 counter and it counts and Ten
LEDs indicate the counts. This can be used as a
Sequential timer or for generating staircase
Press the Red button below to turn on the circuit
press it again to turn off, i have put a new battery
and did the wiring for you. The Red LED will flash
according to the state of the 555 output at pin 3.
The decade counter-divider CD4017 has 10 outputs,
for every low to high transition, rising edge, the
counter advances one LED. After going one full
circle the the first LED lights again and it goes
You can vary the value of R2 using the
controls below to make LEDs run fast or slow. The
frequency of oscillation of astable 555 is given as
f = 1.44 / ((R4 + 2 * (R2 + R3)) * C3).
The 10 outputs have 10 green LEDs. The current
thru the LED is limited by R1, the current can be
calculated like this (9V - 1.6V) / 1K = 7.4mA
this is within 20mA which is the danger limit of the
CMOS output. You want it to be bright use
transistors for every output.
The cap C1 is a filter and C2 is to prevent noise at
pin 5 influencing the output as it is a control
You can cascade or chain many more counters with the
CO or carry out pin 12 of 4017. The pin 15 reset is
kept at low for counting, on high it will reset the
counter but is not used in this circuit.
(i created some confusion with this sentence and i
got muddled up myself when answering some email from
youngsters, as these were things i did when i was a
kid. Cascade means in mathematical sense not in the
"Bike Lights" sense. So when you cascade - the first
set of ten is "Units", the next stage is "Tens" the
next is "Hundreds" ... It becomes a Non-7-Segment
Led number display. The "Bike Lights" of greater
than 10 LEDs can be done with shift registers...)
555 Oscillator and Decade Counter xml use
iframe part for your Webpage or Blog.
the above circuit in pdf format del00017.pdf
the cadsoft eagle source of the circuit del00017.zip
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