resistor calculation

Discussion in 'The Projects Forum' started by sangpo, Aug 17, 2013.

Aug 17, 2013
74
1
Sir/madm . Using 7805 , i want to make my own varaible voltage .ie. 3vdc,6vdc and 12 vdc. so in this case , how do I calculate value of resistor for 3vdc, value of resistor for 6vdc and value of reistor for 12vdc. Please help me here
thank you

2. tubeguy Well-Known Member

Nov 3, 2012
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You really can't make a proper 3 volt regulator using the 7805 and resistors.

An LM317 would be better and go even lower than 3 volts.

3. #12 Expert

Nov 30, 2010
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I have too much time that I need to waste today.

• LM317 with formula.png
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4. tubeguy Well-Known Member

Nov 3, 2012
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Can I buy some extra time from u ??

EDIT : Yard Work

Last edited: Aug 17, 2013
5. Metalmann Active Member

Dec 8, 2012
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Is that for real? That's all there is to it?

6. tubeguy Well-Known Member

Nov 3, 2012
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Maybe

The thing is, learning what the available components can do.

Years ago It wasn't (quite) as tough.

Now, it's a bit mind-boggling (In my opinion)

But, I still appreciate stuff that glows

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7. shortbus AAC Fanatic!

Sep 30, 2009
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Wish I could get to that point! I seem to have got hooked on the smoke.

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8. #12 Expert

Nov 30, 2010
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Sorry. Already stuck with yard work. Finished a plumbing job at 5 pm. Have to wait until 7:30 pm when the heat index goes down to 93 degrees so I can mow the lawn. (Mowing sucks in August in Florida!)

9. tubeguy Well-Known Member

Nov 3, 2012
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A little smoke, once in a while is a good thing ...

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10. tubeguy Well-Known Member

Nov 3, 2012
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How in the heck can you STAND plumbing !%\$#@\$#^%# ???

I have boxes of plumbing pieces that don't fit what I need at the moment.

EDIT: I HAVE plumbing stories .......

11. #12 Expert

Nov 30, 2010
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It comes with the territory, but among things I don't like to do, from worst to less worst, the list goes:

Painting
Plumbing
and gets better from there.
There's nothing quite like laying in a puddle of poop water, trying to fix ruined metal, while the mosquitoes try to eat you alive...and yet, I hate painting even worse.

12. tubeguy Well-Known Member

Nov 3, 2012
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#12,

Does it still rain every afternoon in Florida ??

13. tubeguy Well-Known Member

Nov 3, 2012
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I hate painting more than anything............

But, what about the ghekos ?? (small lizards how do you spell that ??)

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14. #12 Expert

Nov 30, 2010
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It has this week.

15. #12 Expert

Nov 30, 2010
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The native lizard is the anole. Geckos (insurance sales lizards) are very rare here.

http://en.wikipedia.org/wiki/Brown_Anole

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16. wayneh Expert

Sep 9, 2010
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Gosh, I enjoy the actual painting. Getting ready to paint - scraping, sanding, chiseling, repairing, cleaning, and on and on - would be considered cruel and unusual punishment if you forced prisoners to do it. Painting goes so quickly and makes such a big difference.

17. #12 Expert

Nov 30, 2010
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I quite agree. Painting is like soldering: 90% of the work is preparation.
The difference is that if painting takes 4 to 6 hours, the preparation time was 40 to 60 hours. Soldering a pipe takes about 50 seconds, so the preparation takes about 8 minutes.

Aug 17, 2013
74
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Thanks for valuable suggestion made by tubeguy. I have gone through the circuit diagrame for LM317. But here, i wan to know how the value of resistor is calulated. And also, from where did we get 1.25 volt.Please kindly explain for me.

Thank you all

Aug 17, 2013
74
1
thanks for the diagrame of LM317. Please kindly explain me how the value of resistors are calculated.
Thanks you somuch

20. #12 Expert

Nov 30, 2010
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1.25 volts comes from the data sheet for the LM317 chip.
The value of the resistors is calculated by using the formula I wrote on the drawing or by using the formula on the data sheet for the LM317 chip.

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