Arduino Forum

Forum 2005-2010 (read only) => Hardware => Interfacing => Topic started by: interzone on Jan 21, 2011, 01:06 am

Title: Arduino nano 5V to 3.3V bluetooth module
Post by: interzone on Jan 21, 2011, 01:06 am
Hi,
I am new in this forum,
so hello everybody.

I hope someone can help me.

I am working on little project with an arduino nano at 5V.
I want to log the various sensors values wirelessly, via
a bluetooth slave serial module, connected to RX0 & TX0 pin of the Nano.

The bluetooth module needs 3.3V for the TX and RX signal.
And the arduino Nano is the 5V version.

Can I connect the Nano TX0 and RX0 directly to the RX & TX of the bluetooth module?

Or do I have to use some resistor to level down the signal?

If someone can tell me, what resistor value I must use.

thank you all and sorry for my english :)
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: weirdo557 on Jan 21, 2011, 01:23 am
you can hook the transmit from the module directly to the arduino, but you have to use a level converter to convert the 5 volt signal to 3.3 volts. a resistive divider should work fine for that.
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: interzone on Jan 21, 2011, 01:57 am
Ok that's what I thought.
Can someone tell me the values of the resistors I must used?


Just for the people who are interested, this is the kind of bluetooth adapter I use.

(http://inter.zon.free.fr/bluetooth1.jpg)

(http://inter.zon.free.fr/bluetooth2.jpg)

I found them cheap on ebay.
The strange thing , is that the module take 5V as VCC input,
but the TX & RX signal are 3.3V.

I dont understand why they dont translate all the signal to 5V TTL..

anyway..

If someone can calculcate and tell me the values of resistors I can use.
It would greatly help me..

thanks to you all..
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: weirdo557 on Jan 21, 2011, 08:26 am
http://www.makingthings.com/documentation/how-to/scale-a-5v-signal-to-3.3v

this should help. and it looks like there might be a small 3.3 volt regulator on that board. i have a similar one that doesnt have the pin breakouts on it and it runs on 3.3 volts directly.
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: simon.monk on Jan 21, 2011, 09:40 am
The TX on the module can go directly to the RX on the Arduino, but you need a potential divider, from the Tx on the Arduino to the Rx on the BT module.
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: simon.monk on Jan 21, 2011, 10:04 am
Oh, and 270R and 470R.

With the 270R from Tx on Arduino to Rx on module and 470R from Rx on module to GND.
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: interzone on Jan 21, 2011, 10:06 am
Ok. Thank you all for your help.

If I understand well,  the bluetooth TX is high enough to trigger
the 5V arduino RX TTL level,  so it can be connected directly.

and only the arduino TX, has to use divide resistors , to level down the signal to 3.3V for bluetooth RX.

That seems good to me :)
So U only need 2 resistors to connect the arduino to the bluetooth module. Perfect.

I gonna try this,  hope it will work.
thanks.
Title: Re: Arduino nano 5V to 3.3V bluetooth module
Post by: simon.monk on Jan 21, 2011, 10:15 am
It should work fine.

I bought one of those modules (but without the base board).

The hard part was connecting the leads to the tiny edge connector.

I also found proving that it worked from my mac quite hard. I tries z-term and just the console, but in the end I found that the Processing example program called Duplex was just the ticket. But remember to edit to change the port index. Run it once and it will fail, but then give you a list of ports, and you can just change the port number.

Good luck!