Microcontroller newbie

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The RC time constant is R * C. So, if you use a 10Kohm resistor and a 20pF cap, you'll get an RC time constant of 200ns, and a frequency of 5MHz.
 
Yeah lol im no math guru so i was lost lol

Code: 
t = R * C

and

f=1 / T

t = time in Seconds
R = resistance in Ohms
C = capacitance in Farads
f = frequency in Hertz

You can use google like:

20 microfarad to Farad

to convert uF to F...
Code: 
uF (microfarads)
pF (micromicrofarads) (picofarads)
nF (nanofarads)
 
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The highest speed would be with a 3k resistor and a 20pf capacitor which would have a RC constant of 3x10^3 x 20x10^-12 = 0.00000006 seconds. This would give a frequency of 16MHz which seems exceedingly high. Maybe someone should check my figures.

Mike.
 

Your math is right, it doesn't exactly seem *exceedingly* high, however, it'd probably be really unstable and unreliable at that speed.
 

20 picofarads = 2.0 × 10exp-11 farads = 0.0000000002

0.0000000002 * 3000 = 0.0000006

But i am getting: 1,666,666.6666666666666666666666667

Would that not be only less than 2Mhz?
 
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AtomSoft said:
20 picofarads = 2.0 × 10exp-11 farads = 0.0000000002

0.0000000002 * 3000 = 0.0000006

But i am getting: 1,666,666.6666666666666666666666667

Would that not be only less than 2Mhz?
Click to expand...

Oooh, your math is a tad bit off.

20E-12 * 3E3 = 60E-9
1/60E-9 = 16.667E6, or 16.667MHz

Google is returning the conversion in Scientific notation, it's useful to us in Engineering notation. Here are the prefixes:
Milli (x10^-3)
Micro (x10^-6)
Nano (x10^-9)
Pico (x10^-12)

Google says 2.0 x 10^-11, which is 20 x 10^-12
 
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so google is wrong? this sux heh.. i can see your 16Mhz now. Which is cool for max. but i bet a tad unstable
 
ArtemisGoldfish said:
Google says 2.0 x 10^-11, which is 20 x 10^-12
Click to expand...

Its funny
Code: 
Google :  0.0000000002
Engineer: 0.0000000002

* 3k = 0.00000006

1/0.00000006 = 16,666,666
How i the heck did i mess this up before? if they are the same. I must be tired heh its 6min to midnight here

Ill be sure to save:
Milli (x10^-3)
Micro (x10^-6)
Nano (x10^-9)
Pico (x10^-12)
 
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It's helpful to use the right exponents if you use exponents on a calculator, and using exponents can really reduce the chance that you'll press 0 too many times in a very small number (or too few times).
 
Why the heck am i getting weird values?

20*10^-12 = 0.0000000002

1 / (3000 * 0.0000000002) = 1 666 666
1 / 0.0000006 = 1 666 666

I thought i was getting 16 but heh maybe im tired ill try in the morning heh
 
AtomSoft said:
Why the heck am i getting weird values?

20*10^-12 = 0.0000000002

1 / (3000 * 0.0000000002) = 1 666 666
1 / 0.0000006 = 1 666 666

I thought i was getting 16 but heh maybe im tired ill try in the morning heh
Click to expand...

You know, you're still messing up the number of 0's you're using. Exponents man, they're useful.
 

i get 16,666,666 only when i do:

2*10^-12 = 16mhz
20*10^-12 = 1.6mhz

Which one am i supposed to use
 
Well, the value of the capacitor is 20pF and so it is 20 x 10^-12. And, 3E3*20E-12 is around 16M. Post the calculation that produced 1.6 MHz.

Mike.
 
Jason

I think that this is a function of the way you are driving the windowz calculator. I get the same result in Unix (ubuntu) as you are if I do 20*10e-12 (because this is besing expanded to 200e-12), however if you do 20e-12*3e3 (and then do 1/x) you get the correct result. In fact I could not get in to work in Windowz at all!

Hope this helps,

Rupert
 
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