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Topic: Powering bluetooth module from Arduino pro mini 5v (Read 1 time) previous topic - next topic

Hi,
I have a bluetooth module rated max at 3.3v, and an Arduino pro mini ATmega168, at 5v. When I power the bluetooth module through a resistor divider (1.2k +2.2k) I get around 1.68v only to the bluetooth module. Can somebody explain to my why this happens? Does anyone know how to power a 3.3v module from a 5v arduino?

Nick Gammon

Resistor dividers are not very good voltage regulators (the drop varies by the current drawn). Look up a proper voltage regulator circuit.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

I didn't know that. As you can tell, I'm completly new to electronics -.- Thank you!!

Runaway Pancake

Try a couple of rectifier diodes (1N4001, 1N4002, etc.) in series.

Code: [Select]

                     |
+5----A_K----A_K-----| BT +V
                     |


Test circuit:
Code: [Select]

                     
+5----A_K----A_K-----| 470?|----Gnd
                   |
                   |
         check for 3V  here                   
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

Docedison

That Circuit Might work, If regulation wasn't important (It will vary about 300 mV from no load to about 200 mA and it isn't very thermally stable, Diodes are commonly used as temperature sensors in IC's like Processors. After all there's a whole lot of diodes in a Processor. It is also missing a 47uF cap. No Power supply should ever be without some bypassing. The voltage will range from about 750mV @ 0 C to about - 500 550 mV @ 80 C @ 100mA current. Not a lot really considering digital electronics but more than enough to vreate problems with any linear circuitry.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Runaway Pancake

Oh, man.
The diodes are sound enough.  The OP's just cobbling something together.
Does everything have to meet ├╝ber-stringent design criteria?
If someone was working on something so critical that 2 mV per deg_C really mattered then he wouldn't be asking questions here anyway.
For that matter, I bet that the BT has on-board decoupling.
The diodes, something that everyone needs several of in his indispensable box of stuff, ought to enable the OP to get on with it - a practical means for the present.
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

Thank you for all the replies! I decided to use a LD1117V33 voltage regulator as described here: http://www.kobakant.at/DIY/?p=563
Hopefully it'll be helpful for somebody else in the future.

http://www.toastedcircuits.com Lightuino LED driver: 16 sources, 70 sinks, remote controlled.  Also high powered LED drivers.

Docedison

Quote
If someone was working on something so critical that 2 mV per deg_C really mattered then he wouldn't be asking questions here anyway.

Yes I agree but what if he had no clue to begin with... What then?

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Runaway Pancake

I guess he has cash to burn and time to wait.
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

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