Flashing LED with 555 timer

Hi Rob, Without a schematic to reference no one will be able to figure those values for you. Just in case you are looking for a good 555 reference here is an online book one of the guys showed me a while back.

http://www.talkingelectronics.com/projects/50%20-%20555%20Circuits/50%20-%20555%20Circuits.html#9A

You can vary the percentage of on to off time with this circuit. You will have to experiment to get it to the frequency where you want it.

John 

Thank you for the quick reply Mr. John and Mr. Paul.

Here is the circuit that I came up with. I am shooting for a 20ms time high with a 1.3 Second cycle time. I found an online calculator at 555 Astable Circuit Calculator

but its very confusing to me at this point. When I change one value it seems to change others throwing me way off. I can't keep up with it. If any of you gentlemen have a better suggestion for me on this circuit I'm listening. Also thanks for the link Mr. John that will be very helpful in my future projects. Also a quick correction. It will be powered with a 9v Battery, not 5 volts as pictured above.

Thank you for the quick reply Mr. John and Mr. Paul.

Here is the circuit that I came up with. I am shooting for a 20ms time high with a 1.3 Second cycle time. I found an online calculator at 555 Astable Circuit Calculator

but its very confusing to me at this point. When I change one value it seems to change others throwing me way off. I can't keep up with it. If any of you gentlemen have a better suggestion for me on this circuit I'm listening. Also thanks for the link Mr. John that will be very helpful in my future projects. Also a quick correction. It will be powered with a 9v Battery, not 5 volts as pictured above.

Hi Rob.

Thanks for your diagram.

I have also visited the page you referenced. The calculator (annoyingly) works based on submitted component values rather than timings, the reverse to what you really need. An interesting point I did take from this page is as follows:

In this type of circuit, the duty cycle can never be 50% or lower.

The following page goes on to say: http://www.daycounter.com/Calculators/NE555-Calculator.phtml

Note that the minimum duty cycle is 50 percent, so if you need a smaller duty cycle you need to use an inverter on the output. 

I don't really have much 555 Timer experience, but from what i have read, this would seem to apply to you.

At this point I would probably put an extra 30p into the project and use an AtTiny85 instead.

Something like this should handle your output inversion.

74AHC1G04GW,125 - NXP - INVERTER GATE, SINGLE, TSSOP-5 | Farnell element14

Hi Rob,

paulellison is correct that what you want to do might be easier to accomplish with a microprocessor. Also for the 5 volt power you are showing on your schematic you will probably not be able to drive 3 LEDs in series. Most LEDs have junction voltages that are high enough so three in a series would be at or higher than 5 volts. The duty cycle you are trying to achieve is 2% at a frequency of approximately 0.77 Hz. The best that the circuit that I posted before can do is 5%. You can drive three LEDs by using a higher supply voltage. I believe that the 555 for example will work with up to 18 volts on some varieties.

John