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need help led circuit Answered

Hello to all I need help to complete this circuit I want to make a flashing sign for my shop window and have to say that i am new to all of this, but a old dog can still learn, i know a few basics and thats about it. I found a 6v dc circuit on one of the sites that uses a 555 timer and 4017 ic and built a bread board circuit that works but it has one led per output 1) i would like to add +- 20 LEDs to each output (10 strings of +-20 leds). Q) what would i need and how? 2) i want to install a pot to alter the flash rate. Q) what would i need and how? I do have a 12v dc reg supply on hand. Please check the circuit picture and let me know what needs to be done to get it to work It would be much appreciated for any and all help received by all the great minds on this fab site MYKEYB



9 years ago

To set your component values, try one of the many 555 calculators on the web.

Like this or or this... (search, you'll find many more.) For adjustablity, substitute a pot for the resistor values.

you will clearly need a transistor (and a base resistor) to trigger the led strings. i doubt the chip alone can supply the needed amerage. what is the Vforwrd on your leds? you may need two or more strings of led/transistor hooked up to the same pins on the 4017 chip.

thats right

you can use more than 1 transistor for each set of leds. for example you can split the group in half and use 2 smaller transistors instead of one large

once you know what base current you want (you can just give it the max allowed base current and it will be ok) you can calculate the base resistor as if the transistor was led

supply voltage = chip output
current = the base current
led voltage of transistor = 0.7 V