Calculations of the astable multivibrator with NE555?

Question

I don't know how to define the values of the resistors and capacitors on the astable multivibrator with NE555.
Tp1 to be 60 seconds and Tp2 to be 180 seconds.
Can anyone help me to define the values of the resistors and capacitors?
Thanks

Answer 1

I answered this question for you the other day before you'd landed on a 555 as the central component for your circuit. Look back at your prior question and you'll also have this answer.

You're looking for a duty cycle of 75% (or 25%, depending upon which way you look at it) with a total time of 4 minutes (3 + 1).

Positive Time Interval (T1) = 0.693 * (R1+R2) * C
Negative Time Interval (T2) = 0.693 * R2 * C

The following uses a somewhat larger capacitor than the 10uF one described in the post above, and this relieves you of having to use such huge resistor values... not always easily found in one's parts box. The data sheet being pointed to by that post is a 40193 CMOS counter, not an NE555. Bad link got in there, I guess. He's usually pretty sharp with his answers, so it was undoubtely just a typo.

In round numbers, you can use a 1.0M (goes between pins 7 and 8), 510K (goes between pins 6 and 7) and 180uF (goes between pins 6+2 and ground) to create 3 seconds / 1 second timing. You'll have to trim out the 1.0M a bit (or use 1% resistors to get the values closer) if you want it more precise, but that'll give you about 3 seconds and 1 second. Link below includes a diagram for your astable circuit, a calculator for values, and a description of the workings of this IC...

http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm
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Answer 2

Here is a datasheet:
http://focus.ti.com/lit/ds/symlink/cd40193b.pdf

There is a chart on page 7 (Figure 3) with a formula under Figure 1. that tells you what values of R and C to use.

Since one of your delays is greater than 100 seconds (max on the chart), but not too far off the chart you can extrapolate. For the 180 second delay, I would use 16 to 18 MegOhm for R and 10 uF for C

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