Connecting the Arduino Duemilanove to a PP1

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jong

I seem to be having problems communicating with the pp1 board.

I am completely new to the Arduino platform, so apologies in advance
if I have connected it up incorrectly.

The output I get is contant, regardless of whether the pp1 is
connected or not and is as follows:

[bmp085demo]
BMP 65535 65535 128 99975
BMP 65535 65535 128 99975
BMP 65535 65535 128 99975
BMP 65535 65535 128 99975

etc

I have it connected as follows:

pp1 deumilanove
P - not connected
D - Pin 4 Analog In
G - GND
+ - 3V3
A - Pin 5 Analog In
I - not connected

I chose 4 and 5 for SDA and SCK as that is what was indicated on the
Arduino site for i2c connections. Your ports library indicates that I
should use Pin 4 for DIO/SDA but pin 14 for AIO/SCK, however the
duemilanove doesn't have a pin 14 so I am confused.

Many thanks

Jon

Posted 15/02/2010 15:09:57
jong

To which JCW replied:

Pin 14 is analog 1.

You can't use a standard Arduino, because it works at 5V, the BMP085 only works up to 3.6V - you probably won't have damaged the chip yet, but you have to be careful: 5V is too much.

You have to use a system which runs at 3.3V (there are several), or use something like the Plug Shield from Jee Labs to do the voltage conversion.

On the software side: the Ports library does not use the Wire library (which uses analog 4 and 5). That's why it can work with any 2 I/O pins as bit-banged I2C bus.

-jcw

PS. This would have been a perfect question for the discussion forum at http://talk.jeelabs.net/ - would ypu mind re-posting there? That way more people can see this issue, and the reply and whatever discussion follows...

Posted 15/02/2010 15:10:38
jong

Thanks to JCW for responding so promptly, I have now ordered the port shield which will hopefully resolve the problem.

Posted 15/02/2010 15:13:28
jong

Help,

I now have the plug shield installed, with exactly the same results. I had a spare PP1 that I did not use with 5V and this is the same, ie all I get is:

[bmp085demo]
BMP 65535 65535 128 99975
BMP 65535 65535 128 99975
BMP 65535 65535 128 99975
BMP 65535 65535 128 99975

Any suggestions?

Thanks

Posted 01/03/2010 17:50:03
jcw

The bmp085demo example uses the Ports library. With the Plug Shield, you're attaching plugs to the hardware I2C pins, i.e. you need to use the Wire library. So you need to re-write the code.

Hm, I can see how this sort of thing is going to cause lots of confusion (already is, probably).

Ports library = software (bit-banged) I2C on arbitrary pins.
Wire library = driver for hardware I2C on analog A4/A5.

Maybe a version of the Ports library can be hacked which uses A4/A5 in bit-banged mode, then at least all the I2C demos would also work with the Plug Shield... I need to look into this.

Posted 01/03/2010 18:05:00
jong

So can I simply change the ports library to use A4 & A5?

Posted 01/03/2010 19:03:29
jcw

If you want to hack the source code: yes - A4 = pin 18, A5 = pin 19.

Meanwhile, I'll ponder on how to do this in a less destructive manner :)

Posted 01/03/2010 19:14:44

jong

OK, success at last!

I have butchered the Ports library so that it is now hardcoded to use the I2C pins and will therefore work with the Plug Shield, not an ideal solution, but it works. the change to Ports.h was as follows:

/ Hard code the Ports library to use the plug shield / I2C pins and ignore the port number called /

class Port {
protected:

    uint8t portNum;
    inline uint8t digiPin() const

        { return 18; }

    inline uint8t digiPin2() const

        { return 19; }

    inline uint8t anaPin() const

        { return 20; }
The IRQ / anaPin was a guess, but I figure I'm not using it anyway.
As I now only have the one I2C bus, is it possible to have more than one BMP085 connected, or would I need a Jee Node to do this? 
Thanks

Posted 02/03/2010 10:58:43

jcw

The BMP085 chip is hard-wired to address 0x77. So no, you can't hook up multiple units to one bus. With a JeeNode, you could have 4. But why would you want that - isn't atmospheric pressure the same everywhere?

Posted 02/03/2010 11:09:15
jcw

Suggestion: "{ return portNum ? portNum + 4 : 18; }" - i.e. port "0" is the hardwired I2C bus? That way the ports library can still be used with normal ports. In fact, that means you could have up to 5 I2C buses on a JeeNode.

Posted 02/03/2010 11:11:31
jcw

I've updated the Ports library so that pseudo "port 0" gets redirected to A4/A5, i.e. uses software I2C on the hardware I2C pins. No impact on existing code, other than perhaps a very slight slowdown and code size increase.

Posted 13/03/2010 18:21:12