# Formula about led flasher & Timer Chip..!!

Discussion in 'General Electronics Chat' started by redlight000, Apr 9, 2010.

1. ### redlight000 Thread Starter Member

Feb 26, 2010
66
2
Hi all,

this is a formular from a good electronic book, & I Just cant grasp on how to enter this on my scientific calculator... it's a Timer rigged in astable mode..

R1=4.7k
R2=10k
C=10uf electroltic cap... the resistor is 1.5k on the output for the Led..
and the above circuit flashes the Led at about 5.8zh.. thats that bit..

Now the author, broke down the equation on how it arrived at 5.8hz..
1/0.7 x 10 x 10 to the negitive power of six x (4700 + 20,000)

now I'VE DONE ALL THE EQUATIONS on the calc, and done them all correctly.. but I cant seem to get this spot on .. 5.8hz can anyone help on that please..??
========================================================

These are the maths done on the calculator.. and turned out spot on..

example 1)

Amplifier gain..
Calculate the value of Av
Voltage gain AV=20 Log Vo/Vi
=20 log 3/1x10 to the negitive power of 3=
69.54242509dB

How to enter that into the calc =
press 3/[EXP]3[+/-] = 1.-03 ON DISPLAY
=[log] [X] 3.477121225 on display
20 = 69.54242509
now I entered all that & yet I cant do the above one ie the 5.hz one its doing my head...

thanks if anyone can help on the top above bit Post..
??
regards redlight000< binary lol

2. ### Wendy Moderator

Mar 24, 2008
20,993
2,731
This should be in the chat forum.

Schematics are needed.

3. ### Bernard AAC Fanatic!

Aug 7, 2008
4,533
476
If the chip is 555, I come up with 10.3 or 8.1 Hz, +- 20%.depending on R1,R2 placement.

Last edited: Apr 10, 2010
4. ### redlight000 Thread Starter Member

Feb 26, 2010
66
2
Hi Bernard,

what you mean you replaced your R1+R2?
because mine IS R1=4k7 4.7k
R2 = 10k 10000 ohms
C1=10uf electrolytic cap
in pins 1+2 of the 555 chip!!
R3 = 1.5k <<< thats coming from pin 3 to the led to limit the current to the led ..
and as I said the author states in the BOOK "after all the math that turns out 5.8hz.. or 6hz per second..
ok
cheers
from
red angry light

5. ### Bernard AAC Fanatic!

Aug 7, 2008
4,533
476
Placement, not replacement; need schematic for further help.

6. ### Wendy Moderator

Mar 24, 2008
20,993
2,731
Which is what I asked for. You no give information, you no get information.

7. ### Jazz Bass Special New Member

Apr 9, 2010
24
5
redlight000 likes this.
8. ### redlight000 Thread Starter Member

Feb 26, 2010
66
2
Hi Bill,
well thats a bit of a problem.. its a bit small in the book you would hardly see it..
Im not that fussed.. on it.. its the calculator thats getting me not the arriaval of 5.8hz thats a diddle
.. lol
cheers m8

Ok I see yur point... I may try...at some later stage..

:_)

9. ### Pencil Active Member

Dec 8, 2009
271
38
Try this:

1/((.7x(4700+10000)x(10x10^-6))+(.7x10000x(10x10^-6)))=

I haven't had a calculator with an [EXP] button for exponents
in several years so I don't remember the exact key stroke sequence
for that part. (10^-6 means 10 to the negative sixth)

Note: Parentheses are required.

redlight000 likes this.
10. ### SgtWookie Expert

Jul 17, 2007
22,194
1,761
If you want to keep it simple, then just shift the decimal place in the resistance instead of using 10x10e-6.
For example:
T1 = 0.7x(0.0047+0.01)x10
T1 = 0.1029
T2 = 0.7x0.01x10
T2 = 0.07
F = 1/(T1+T2)
F = 1/(0.1029+0.07)
F = 1/0.1729
F = 5.7836899942163100057836899942163

redlight000 likes this.
11. ### Wendy Moderator

Mar 24, 2008
20,993
2,731
Windows calculator has a scientific mode, but I keep a calculator next to my keyboard just for these kind of calculations.

12. ### retched AAC Fanatic!

Dec 5, 2009
5,201
315
Pbbbbtt.. I use my fingers. And I lost two of them in a lawnmower accident.

kidding.. If you want a good replacement for windows calculator with a bunch of good scientific options, try calc98. calculator.org

From roman numerals to the periodic table of elements.. just everything you need. and its free.. Also It runs on linux under Wine.

redlight000 likes this.
13. ### Wendy Moderator

Mar 24, 2008
20,993
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redlight000 likes this.
14. ### redlight000 Thread Starter Member

Feb 26, 2010
66
2
Hi Pencil.
Nope I tried entering it.. then I get stuck on what to press.. div head me) EYES rolling,
thanks though

15. ### redlight000 Thread Starter Member

Feb 26, 2010
66
2
Hi Sgtwookie,
you are a maths Wizz I done it!!!! yepeeeeeeeeeeee
thanks very much for inputing all that.. for me I do really think alot of that.. although I dont normally show it... thanks again..you genius...

regards
redlight000

16. ### redlight000 Thread Starter Member

Feb 26, 2010
66
2
Hi Bill,
thanks for that.. see as stupid as I feel, I still cant grasp some of the maths, you kindly put up.... If Im honest.. with the math side I can do it.. as you can see from the posts on here... wait..) but not all see what I go by is "Starting Electronics by Keith Brindly) Fab book & learnt so much from that.. I normally start R1 as 4.7k & R2 as 10k.. and then choose C/ for the freq) which I've got Mimms small hand book,

So that give me a rough Idea on how to get say a 1000hz or 7hz.<< not exact though...
thats how I go about it."YES" I do the maths,, you have to if I design my own sound generators & flashers etc... blast that VERY bright red Led ... in a different post.. that made me ill...
thanks again...
regards
redlight

Dec 8, 2009
271
38