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555 Oscillator and Decade Counter - doc00020This 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 javascript simulation i made.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 on..... 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 voltage point. 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.
the above circuit in pdf format del00017.pdf the cadsoft eagle source of the circuit del00017.zip datasheet of LM555 here pdf. datasheet of CD4017 here pdf. pdf links may take time to load in the browser, save file target to your disk is better. If LEDs are not lighting up, refresh the page. Tested in Mozilla 1, Opera 5 and IE5 with javascript and images enabled. |
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555 Output
