Let's Make Robots!

Quick resistor question: 3,3 V from 4,07

I am not too proud to ask:

I have a LiPo supplying nominal 3,7V -- 4,07 at the moment, possibly fully charged.

I also have a gyro sensor that ask for 3,3 V - and I'd hate to fry it.

I really, really cannot understand the law of Ohm, so I am asking, can any one tell me what to throw in there?

Thanks :)

 

(Oh, and any tips on brown out detection would be appreciated; I'd hate to discharge my LiPo, but am trying to keep this simple, becaue that is my style ;) - Any smart tips on making sure it will not go too low?)

ThankyouThankyouThankyou!

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Hi, DISCLAIMER: Mentioning stuff from my own shop... but that's where I have the cool stuff :-)

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=215

Includes 2 of the 3.3V Ldo regulators in easy to connect TO220 pkg...

 

Terry

 

 

... a Zener diode rated for 3.3 ususally marked 3v3 as the ones on this page:

http://parts.digikey.ca/1/3/zener-3v3-1w

Anyone correct me if I'm wrong :)

Since the gyroscope doesn't use much current you should have no problem finding an ultra low dropout voltage regulator, but I think they are typically surface mount devices. This will allow you to regulate to 3.3v from anything around 3.4v and above. It could be simpler to use two lipos in series and a regular regulator if smd is a problem.

Thank you guys, 3 good tips, all I needed, thank you :)

What I do is hook up the battery to a 10k pot. Add your measure thingie and adjust the pot until you get your 3.3v. Now disconnect everything and use the ohm setting on the multimeter to measure each side of the pot. These are the values of the resistors you will need to build your resistor bridge.

yes a voltage divider , now that's simple nice 1 CTC

Isn’t a voltage divider linear so that when the battery voltage goes down so does the divider output?
I think that a regulator or a zener diode is a better solution.

i had a rc helicopter that had a low battery light connected, it was a small gizmo that attached to the main battery  with a blue light that would flash when the battery is getting low 

link

http://www.bphobbies.com/view.asp?id=V426371   

as for your gyro 3.3V from 3.7- 4.07 you could find a suitable regulator  that won't drop out at low voltage , but not a lot of head room there so i think it's unlikely.

what dose the speck sheet say about voltage tolerance you may have some space to move there   ,

Since the output varies, I would go with a regulator. Like a LD1117V33 for example, you want to couple it with a 10μF capacitor though, to keep it stable and nice.

 

A cap that small won't drain the battery :)