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# 555 timer formula's

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#### kd7jur

##### New Member
Ok so i tried posting this in the Theory forum, but the forum wouldn't let me...

So i need to know the formula's for a 555 timer for my C programming final project. the problem states:

"Create a program that will provide all 555 timer components necessary based upon the required frequency and pulse width."

so now the question is, what is this formula, i'm assuming it's set up in astable configuration, because of the frequency part.

Thanks for any help

The formula you are looking for is on the 555 data sheet.

Thanks, i'll go look for it

Apparently i don't see them...

Hi,

here they are.

Boncuk

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• NE555.gif
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test test test ignore

Hi,

here they are.

Boncuk

Yeah i have all that, i need to find R1, R2, and C1 by giving Frequency, and Pulse Width (Time high?). i've narrowed it down to solve an equation for two variables, Time Low, then figure the rest.

Can you make some reasonable assumptions based on what sort of components are available. eg: spec'ing a 434 uF cap or a 1.72 k Ohm resitor would be difficult to actually implement anyways.

Your teacher wants you to take in Freq and pulse width. I would interpret that as enter Hz, then enter a number representing pulse time high. Of which the easiest way I am aware of is as a percentage where 0 % is always low and 100% is always on. So for 0 > pulse width < 100 would represent what percentage of the period is on.

Something like this for pulse width per cycle:

10% -_________

20% --________

30 ---_________
.
.
.
90 % ---------_

calcs

see the attached zip file

#### Attachments

• 555 calcs.zip
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Can you provide some more of the constraints for your design? Is your teacher requiring that your program provide component values for a specific 555 chip or generic values. Can you use integer frequency or will you also need to provide values for decimal freq and integer or decimal duty cycle?

GOT IT!!!. I built the program, and it works.

File Attached, check it out.

Thanks for all your help. with a lil help from one of my insturctors, i found on the data sheet more info to help me.

#### Attachments

• ET156 Final Project.zip
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