# Convert V to mV

Discussion in 'General Electronics Discussion' started by Electro132, Aug 6, 2013.

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1. ### Electro132

261
3
Feb 12, 2013
Hi Guys,

Thanks for the help in the past. Things with the other projects are going fine.

I have a new project and it has to do with converting V into mV. I was thinking of having an input of 9V and converting it to an output of 80 mV.

Can anyone help? This is hard to do.

Thanks

2. ### GreenGiant

842
6
Feb 9, 2012
How much current do you need?
if its not much then a simple voltage divider will work, though it will be a bit of a waste.

3. ### Electro132

261
3
Feb 12, 2013

I need to have an output of at least 80 mV so according to ohm's law

I = V/R

I = 0.08 / 10 = 0.008

I = 0.008 Amperes

I was looking online for something that could give me the resistors, caps and other stuff for the circuit but came close to nothing. So far the net has told me to use a voltage regulator lol

But i'm having difficulty trying to convert it from either 3v, 12v or 9v to get 80mV (0.08 V)

4. ### GreenGiant

842
6
Feb 9, 2012
while your math is correct you are solving the wrong formula.

I was asking how much current that you needed to base what resistors to use (the more current you need the larger the wattage and lower the resistance needs to be)

in order to get .08V out of 9 you need a ratio of about 112.5 : 1 so theoretically you need a 111.5 ohm resistor then a 1 ohm resistor in series with each other and you tap right in front of the 1 ohm.

9*(1/(111.5+1)) = .08V

but being a strange number you would be more likely to go with either a 100 or a 110 ohm which would leave you with .09 or .081 respectively, either of which would probably work.

This would also only leave you with .08A approximately, so if you need more than 80mA of current you are going to have to use smaller resistors.

5. ### Electro132

261
3
Feb 12, 2013

Not sure yet how much current. Btw, What do you mean by 'tap' and how do i do that technique?

6. ### GreenGiant

842
6
Feb 9, 2012
Thats just a term I use, you will have 2 resistors, the larger of which will go first you want to connect what you need to supply the 80mV with after the first resistor or before the second

+V--->110 ohm----->1 ohm ----> -V/GND
|​
V​
Part needing 80mV​

Drawing didnt work perfectly but I hope you get the idea

Last edited: Aug 7, 2013
7. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
If the first guy to use ASCII art is still alive I'd like to whack him with a bat. If he's dead and gone I'd like to dig him up and whack him with a bat anyway!

Chris

8. ### BobK

7,682
1,688
Jan 5, 2010
But that would be cruel and unwarranted. When the first guy used ASCII art, there were only fixed width fonts. It is the proportioanal fonts that screwed it up.

By the way, I was one of the creators of the classic ASCII animation of Bambi vs. Godzilla.

Bob

Last edited: Aug 7, 2013
9. ### BobK

7,682
1,688
Jan 5, 2010
How about telling us what you want to do with he 80mV?

Bob

10. ### Electro132

261
3
Feb 12, 2013

Thanks the drawing is fine, but don't i need a diode just in case the battery is placed in the wrong way? Also, the current i am seeking is - 80 mV not + 80 mV.

So i think the current for this is something like 0.1 - 0.3 but i want to use this current like a radio station so it's like the current 0.1 being transmitted within a range of 10 kilometres. Can you help me out?

11. ### Electro132

261
3
Feb 12, 2013
Well i want to project it out within a range of 10km kind of like a radio station sending out their signal.

12. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
Is that the one where Godzilla's big foot crushes Bambi?

Huh? What does that mean?

Chris

13. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
2,837
Jan 21, 2010
I guess the next question is "how do you intend to do that?".

80mV is an itty-bitty voltage that, on its own isn't going to do anything. If this is the input to some transmitter then needing 80mV DC seems odd.

I think what we're getting at here is that you may have some other problems down the line and that "needing" 80mV is a symptom of that.

14. ### Electro132

261
3
Feb 12, 2013
No, no actually it is the output - - 80 mV is the output. The input is - well i set it at 9v. This is possible isn't it? i could go higher but not too sure right now

15. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
2,837
Jan 21, 2010
Can you explain how that itty bitty DC signal is going to be "projected out"?

I'm pretty sure you don't understand something, and if you explain what you're thinking we can tell you where that misunderstanding is.

16. ### davennModerator

13,833
1,950
Sep 5, 2009
Not with the way you have described so far

What EXACTLY are you trying to achieve .... full description

cheers
Dave

17. ### Electro132

261
3
Feb 12, 2013

Ok, ok. Here's the experiment i'm doing: To emit and receive a signal between the -70 mV and -80 mV range using pulsated LD's.

Now i know it might sound crazy, but apparently it's possible

That is the full description. That is why i wanted to convert 9v or some other source between -70 and -80 mV

18. ### CDRIVEHauling 10' pipe on a Trek Shift3

4,960
652
May 8, 2012
So you want to setup a 10KM Laser Diode transmitter - receiver? I still don't see how your question relates.

By the way, Lasers are "Line Of Sight" devices. Have you considered the following limitations?

http://www.ringbell.co.uk/info/hdist.htm

Chris

19. ### BobK

7,682
1,688
Jan 5, 2010
Yep, I did that. It was based on an actual cartoon of the same name that I saw at an animation festival.

Bob

20. ### Harald KappModeratorModerator

11,513
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Nov 17, 2011
I don't know any laser diode that operates from 80mV. I'm sure you have gotten something wrong - conceptually. If you want to measure a signal in the range of 80mV and transmit the measurement using laser diodes, you'll have to modulate the Laser diode current in a suitable manner and you will have to demodulate accordingly on the receiving end.

By what means ever you are going to transmit the signal: The larger the input signal, the better the transmission. Arbitrarily reducing an input of 9V to 80mV for transmission is contra-productive.

Last edited: Aug 9, 2013