USB 5v to 3.3v What is the best way to do this?

[alfa147x]

I need to take 5v from USB to 3.3v. I am trying to adapt a bluetooth from a macbook pro for my desktop.

I would prefer to be able to pick stuff up from the local radio shack so I can get it working this weekend. Could I use a LM317T with a 200 ohm resistor for R1, and 330 ohm for R2, which would equal 3.31v? (right?)

Is their a better route?

Thanks!
Alfa

 

[cornbread]

I need to take 5v from USB to 3.3v. I am trying to adapt a bluetooth from a macbook pro for my dekstop.

I would prefer to be able to pick stuff up from the local radio shack so I can get it working this weekend. Could I use a LM317T with a 200 ohm resistor for R1, and 330 ohm for R2, which would equal 3.31v? (right?)

Is their a better route?

Thanks!
Alfa

Got drivers?

 

[alfa147x]

Got drivers?

for the bluetooth adapter? No need OS X has them built-in

 

[Eli]

78L33 would probably be easier than the LM317...

 

[PottedMeat]

oops

 

[PottedMeat]

I need to take 5v from USB to 3.3v. I am trying to adapt a bluetooth from a macbook pro for my desktop.

I would prefer to be able to pick stuff up from the local radio shack so I can get it working this weekend. Could I use a LM317T with a 200 ohm resistor for R1, and 330 ohm for R2, which would equal 3.31v? (right?)

Is their a better route?

Thanks!
Alfa

that's fine, add some input and output 6.3V+ rated capacitors ( find some ballpark values on a datasheet ).

and if you have difficulty finding the resistors any values that give you ~3-3.6V should be good.

 

[Drako]

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=AP130-33SAG-7-ND

AP130

 

[Eli]

Somehow I doubt he wants to deal with SMD..

 

[Drako]

Somehow I doubt he wants to deal with SMD..

Why does it matter?

 

[alfa147x]

Thanks guys but I ended up ordering this:

$4


Input Voltage: 4.75-6VDC
Output voltage: 3.3VDC
Max output current: 700mA
Compact size

The black thing is the voltage regulator and those two tiny yellow/brown things are resistors. The 2 larger yellow things are those the capacitors?

 

[Eli]

They're all caps. No resistors on that board(unless they're on the bottom side). SMD resistors are almost always black. And they're labeled C1 and C2.

And SMD matters because it's very difficult to do DIY stuff with.

 

[Jeff7]

Doesn't all USB run at 5V?
Why do you need to convert voltages?



In my semi-educated opinion, you'd be looking for a buffer or level-shifter.
A voltage regulator won't have the turn-on time needed to send a high-speed signal.

Buffer.

As I understand it, you'd supply +3.3V to that chip's VDD pin, and then apply the 5V input signal to one of its input pins, then the output will be about 3.3V.
There's going to be a delay between applying the signal to the input and the signal coming out the other side. This might screw with timings and data integrity.


Also, page 10 here - bidirectional level-shifting with simple MOSFETs.

Thanks guys but I ended up ordering this:

$4


Input Voltage: 4.75-6VDC
Output voltage: 3.3VDC
Max output current: 700mA
Compact size

The black thing is the voltage regulator and those two tiny yellow/brown things are resistors. The 2 larger yellow things are those the capacitors?

LM1117. A basic linear voltage regulator.
The 2 large yellow things are tantalum capacitors.
The small tan things are ceramic capacitors.
Linear regulators reduce voltage by converting the excess to heat. So if you've got 500mA through the regulator, that 1.7V difference (5V-3.3V) * 0.500A = 0.85W of heat generated.




*** - standard disclaimer: If you blow up your laptop or rupture spacetime, not my fault.

 

[Gibson486]

Doesn't all USB run at 5V?
Why do you need to convert voltages?



In my semi-educated opinion, you'd be looking for a buffer or level-shifter.
A voltage regulator won't have the turn-on time needed to send a high-speed signal.

Buffer.

As I understand it, you'd supply +3.3V to that chip's VDD pin, and then apply the 5V input signal to one of its input pins, then the output will be about 3.3V.
There's going to be a delay between applying the signal to the input and the signal coming out the other side. This might screw with timings and data integrity.





LM1117. A basic linear voltage regulator.
The 2 large yellow things are tantalum capacitors.
The small tan things are ceramic capacitors.

heh...I was thinking the same thing. Glad someone thinks like I do.

 

[alfa147x]

Well here is the thing:

My hackintosh with my Apple Magic Trackpad have been having some trouble BUT my MacBook Pro doesn't have any trouble running the trackpad. So I bought the bluetooth module that is in the MacBook Pro and on it it says 3.3v

So at the end of the day of bad of a decision was it to buy that part?

 

[Leros]

If you just need 3.3v power, then you're fine.

If you need to convert data from 3.3v to 5v (and vice versa), then you need a level converter.
This would do: http://www.sparkfun.com/products/8745

You probably need both. The 3.3v regulator to power the device and the level shifter so it can interface to the USB.