Is this normal? Do all the devices connected on an i2C bus have to be powered up all the time for the bus to work? Are there any work-arounds?
The UNO has a 3.3V v.reg on-board, while some of the other boards like Duemilanove do not. Are you actually using a UNO board or just a UNO chip? What voltage are you measuring at the 3V3 header pin when disconnected from USB?
No, this is not normal. Usually an inactive device sets it's bus line to high-imp and doesn't affect the bus anymore.Your description sound a bit like the USB device having the relevant pull-ups installed. Can you provide links to the datasheets of the two devices connected to your bus? And, if possible, a diagram of how you wired everything up?
Well the Duemilanove board does have a on-board 3.3vdc voltage regulator supplying the 3.3v pin, but it happens to be mounted inside the FTDI chip and carries a 50ma max output current.
QuoteWell the Duemilanove board does have a on-board 3.3vdc voltage regulator supplying the 3.3v pin, but it happens to be mounted inside the FTDI chip and carries a 50ma max output current.Right, I forgot to say that 3V3 goes away on the Duemilanove board when the USB is disconnected from the PC. No? Hmmm, I thought the 3V3 went away on mine, but now it seems maybe I was just loading it too much. ? 50-mA is nothing. [unfortunately, some guy borrowed my Duemilanove so I cannot check].
No, the FTDI chip gets it's Vcc from the same +5vdc bus that powers the AVR chip.
QuoteNo, the FTDI chip gets it's Vcc from the same +5vdc bus that powers the AVR chip.Yeah, I just looked at the Duemilanove schematic. I must have overloaded the measly50-mA. Hmm, this makes for a real PITN when stacking bds, as you cannot even bypass that3V3, and supply your own 3.3V power from above. Probably low the FTDI chip.
The datasheet for the USB device is quite basic but you can see it in the link below:http://amanero.com/drivers/combo384-D.pdfI am not having much success in getting my I2C queries resolved by the Designer - he is desperately trying to write a Windows driver for the device.
This device doesn't have an I2C bus but an I2S bus. I don't know the I2S bus but it doesn't seem to be compatible with the I2C bus electrically (active high instead of low and high > 2V instead of the >3V of the Arduino). The logical system seems different too. How do you get the impression that this device will be I2C compatible?
How do devices normally set their I2C bus connections to high impedance when unpowered? Are there any standard solutions?