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I have connected up a BMP085 barometric pressure sensor (breakout board) from sparkfun to an arduino nano using the i2c bus (A4 - SDA and A5 -SCL) and it doesn't seem to be recognised by the arduino.

I've run the arduino i2c scanner (http://arduino.cc/playground/Main/I2cScanner) to see if anything is connected and it returns "No i2c devices found".

Does anybody know what's going on?

BMP085 Sensor Link - http://proto-pic.co.uk/barometric-pressure-sensor-bmp085-breakout-new/
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Did you connect the VCC pin to 5V (wrong) or 3.3V (correct) and Ground to GND?
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I've got the VCC pin going to 3.3v and GND to ground.

Have you got to configure analog pins 4 and 5 for i2C or is that what the wire library does?
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Here is a picture of the circuit layout and I can't see much wrong. I've also tried using the adafruit library (https://github.com/adafruit/Adafruit-BMP085-Library) and this too says that the sensor cannot be found.

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It's pretty difficult to see what pin each jumper is going to but assuming you have it wired as per this tutorial (substituting for relevant Nano pins) http://bildr.org/2011/06/bmp085-arduino/ and using there example sketch, if it still does not work then I can only assume a faulty Nano or BMP085.
One final though!
Just to reduce possible breadboard problem, jumper the 3.3V & GND directly to the relevant BMP085 pins instead of using the +- rail on the breadboard.
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I have just tried wiring it directly instead of jumping around the breadboard on both an arduino nano and uno and neither picks up the sensor.

However, on the nano just after uploading the sketch I keep getting this pop up at the bottom "avrdude: stk500_getsync(): not in sync: resp=0x00".
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I have just tried wiring it directly instead of jumping around the breadboard on both an arduino nano and uno and neither picks up the sensor.

However, on the nano just after uploading the sketch I keep getting this pop up at the bottom "avrdude: stk500_getsync(): not in sync: resp=0x00".
If you have tried it on 2 separate microcontrollers Nano and UNO and it still does not work then it looks like a dead BMP085. If it ever got fed 5V for VCC it may have destroyed the device.
Not much of an idea on the stk500 error apart from remembering to set the board type in the IDE before uploading the sketch.
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Ok, thanks. I pretty sure that I haven't connected it to a 5V supply.

Looks like I'll be sending it back then!
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I gave it one last chance and fiddled around with a few of the wires and it miraculously worked! I think the jumper wires that I have aren't very good.
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Glad you got it sorted.
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