Very special NE-555 calculator Input Period and duty-cycle obtain C, R1, R2

Hi everybody,

I have quogled for NE-555 online calculators and - of course - found multiple of them.
But all the ones that I found work this way
choose mode: astable
input capacity
input R1
input R2
get the results for

  • frequency
  • On-time
  • Off-time

with this kind of calculator I would have to play around a very long time to finally get a combination that does
have a period of 35.000 milliseconds
on-time 1 millisecond
offtime 34 milliseconds

Does somebody know of a NE-555-online-calculator that is able to calculate
capacity, R1 and R2 for a given combination of
period, Ontime and offtime ?

I guess this must be done by a software that does a numerical aproximation by sweeping the values of capacity, R1 and R2

best regards Stefan

I use the ElectroDoc Pro app and it has a 555 timer I've used before that seems to work well.


Hi @apf1979
thank you for answering.

Did you really test it the way I will describe below:

I tested the free-version.

But I am unable to input frequency and dutycycle.
The only thing that worked was entering R1, R2, C

But I want the opposite
I want to enter frequency and dutycycle and get

the result shall be
capacity, R1 and R2 as the result

Is the pro-version able to work

enter

frequency 28.571428571 Hz
dutycycle 1 millisecond ON 34 milliseconds off

and as the

result

get suitable values for capacity, R1, R2

best regards Stefan

Yes, for me I can enter the frequency or duty cycle and it gives me the R and C values. I don't know if it's because I have the pro version or maybe a different revision, etc.???

Can't you make a spreadsheet to calculate what you need? I also have ElectroDoc the free version and see no limitations.

Hi,

thank you very much for answering. I finally was able to calculate the values.
I was assuming too fast it can't do it.
Very interesting to getting to know the possible applications and the limits.

If I understand right you can achieve a wide range of frequency and duty-cycles from 0,X Hz up to 500 kHz.

But as the determing components the capacitor C and R1 and R2 are in series varying one value has a direct effect on the other two values too.

This means if you want to adjust for example the frequency to a certain value by changing capacity this will require to change R1 and R2 too to keep the same dutycycle. And this effect occurs for changing dutycycle too.

So from this I have learned that the NE-555 can produce a wide range of frequency and dutycycle but adjusting to very precise values is an iterative process of adjusting all three C, R1, R2

best regards Stefan

Not necessarily. There is a circuit with 2 rectifier diodes added so that the two ON and OFF times can be adjusted independently. With the 555 timer I never got accurate results as predicted. Even the datasheet statement that frequency is independent of supply voltage is not entirely true. I have actually used a 555 timer very little and that was many years ago. Honestly now I'd rather program some kind of microcontroller for the purpose instead of having to deal with the limitations of a 555 timer.

On this 555 Circuits Part 1 - The 555 Timer Astable Oscillator see ' An Improved Duty Cycle' and ' Fully Independent Timing Periods'.

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