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Topic-icon BlueTooth SPP link?

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11 years 5 months ago #26662108 by datac99
BlueTooth SPP link? was created by datac99
Hey Folks,

I was wondering if anyone had successfully managed to get serial communication working over a BlueTooth SPP (Serial Port Protocol) link?

I'm trying to use a BlueSMrF ( www.sparkfun.com/commerce/product_info.php?products_id=158 ) connected to the controller and another generic BT dongle on my PC.

So far I have been able to communicate just fine with the remote BT module. As near as I can figure out the port settings are right (9600,7,E,1)... But when I try to use Roborun it never finds the controller.

I get some garbage characters on the terminal when I power cycle the controller... So it seems like a have some sort of issue with the port settings but if this were the case I would not expect to be able to talk to the remote BT module at all.

The following is a settings dump from the module:
***Settings***
BTA=000666009FFF
BTName=Remote
Baudrt=9600
Parity=Even - 7BIT
Mode =Slav
Authen=0
Encryp=0
PinCod=1234
Bonded=0
Rem=NONE SET
END

And this is the string of garbage ascii which I assume is the controller sending out it's welcome string:
9Z5y'x>9
Z

Anyone tried this? Got any general ideas? The serial cable that came with the controller / roborun works just fine... So the problem is obviously with something I'm doing... But I'm out of ideas.

There was some mention a few posts back about the signal being inverted when connecting the module to a pic useing a 5K resistor to knock the voltage down... Could this be my problem? Is there any way to check?

I'd appreciate any and all ideas... Thanks -PM

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11 years 4 months ago #26743580 by datac99
Replied by datac99 on topic BlueTooth SPP link?
Okay so I was pretty frustrated when I posted this a few days ago... Having spent the better part of the morning figuring out that I needed to send a capital "B7,1" rather then a lower-case "b7,1" to my BT module to get it into 7-bit mode...

So I know what I posted above isn't really enough information for someone to cough up a solution... But I was really hoping someone here would have some guidance on how I might troubleshoot this.

So in addition to the basics I've got a DSO but thats about it. I'm sure I could capture the controller connection sequence over a standard serial cable and compare it to whats coming out of the remote end of the BT link but given my general lack of knowledge of RS232 I'm not sure this would yield anything useful. Is this the best place to start? Does anyone have any other ideas?


Best Regards,

Peter M.

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11 years 4 months ago #26804352 by datac99
Replied by datac99 on topic BlueTooth SPP link?
Right... So I guess I'm a moron...

This is what happens when you just dabble in this stuff... A lifetime of using RS232 and "Serial" as interchangeable words... Somehow even though I read about this my head was just stuck on the idea that RS232 = serial = 0 - 5v logic... *sigh*

I don't know why I had to actually see this on the scope before I got it... I must have read this 5 times over the last few days but it finally stuck.

The controller uses RS232 serial signaling with -9v being a logic 1 and... Well it looks like 0v as a logic 0... Though I'm assuming I'm just reading the display on the scope wrong here cuz' it should be 9v as a logic 0.

My bluetooth serial link wants +5v for it's logic 1 and 0v for it's logic 0.

So the answer it would seem is: www.sparkfun.com/commerce/product_info.php?products_id=449 a bidirectional RS232 level shifter. And I just happen to already have 2 sitting here!

I'll come back and update this with a schematic when I get it working... Hopefully there is a least one other person who hasn't figured this out yet :-)

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11 years 4 months ago #26851496 by datac99
Replied by datac99 on topic BlueTooth SPP link?
Mummmm.... Not so much on spark fun level shifter... Unless I'm misunderstanding how to use the thing it just doesn't seem to be good for much in this application.

I'm not sure why either... When I was testing earlier I had one BT module plugged into the computer with one of the level shifters in between...

The other BT module was hooked directly to a serial VFD display and I was able to send text from Hyperterminal to the display. But with the controller at the other end I get some like -9v on the RX pin and 0v on the TX pin... Roborun in banging away like mad trying to send it's init string... I can see the pulse train on the low voltage side of the level shifter but not the high side...

In fact when I look at the schematic for the shifter I'm not even sure how it's supposed to work :-) Not that I'm generally sure how things should work when I read the schematic... But this one is pretty simple and it's still got me confused...

I guess I'm going to try to resetup my previous test with just the BT module / shifter / VFD and Hyperterminal and see what kind of readings I get from the shifter then.

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11 years 4 months ago #26858531 by datac99
Replied by datac99 on topic BlueTooth SPP link?
So I guess I need something more like a MAX232 ( en.wikibooks.org/wiki/Serial_Programming:MAX232_Driver_Receiver ) or ILC32XX chip to pull this off... I HATE having to order parts.

Though it seems like I could rig up something similar to what cosmo mentioned in the "RS232/TTL" post with a diode and pair of transistors to invert the logic... Wait... That sound like what's in spark fun's level shifter...

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