navX Micro I2C voltage and Roborio

[cpapplefamily]

I been digging around the documentation. The navX is a 5v board and the RoboRIO Onboard I2C Interface is 3.3v http://pdocs.kauailabs.com/navx-micr...-installation/. The MXP-Expansion I2C ports seem to be 5vdc. Should I understand this to mean we should use the MXP-Expansion I2C interface?

reading on at the bottom of the page

Electrical Notes

The I2C bus standard requires that the SDA and SCL pins be pulled up with a pull-up resistor on each line. The RoboRIO internally pulls these lines high – but if connecting to a host computer without pullups, the SDA and SCL lines will need 1.5KOhm pullups.

The navX-Micro I2C pins are 5V tolerant, so the host computer can use either 5V or 3.3V DC levels on these pins.

I read this as the SDA and SCL lines are 5v tolerant. Dose the 5v pin and the NavX Micro still NEED 5v?

Then even this page suggest using the USB preferably.

[aeastet]

We at Kauai Labs are launching the USB support for all languages for the kickoff. It is a much fast interface and that would be the preferable method.

The maximum sample rate for the I2C is 50Hz for the micro through the I2C port. The maximum sample rate for the USB will be 200Hz for the USB. You will need the firmware for version 3 and the new libraries to accomplish this.

I hope this helps,

Tim

[aeastet]

Originally Posted by aeastet

We at Kauai Labs are launching the USB support for all languages for the kickoff. It is a much fast interface and that would be the preferable method.

The maximum sample rate for the I2C is 50Hz for the micro through the I2C port. The maximum sample rate for the USB will be 200Hz for the USB. You will need the firmware for version 3 and the new libraries to accomplish this.

I hope this helps,

Tim

I talked with Scott earlier and he informed me that the TTL UART connection is the only connection with a 50Hz limitation. To be clear any connection for the navX-micro or navX-MXP should be capable of 200Hz sample rate with the version 3 firmware and the new libraries launching soon.

Sorry for any confusion.

Tim

[cpapplefamily]

Originally Posted by aeastet

We at Kauai Labs are launching the USB support for all languages for the kickoff. It is a much fast interface and that would be the preferable method.

The maximum sample rate for the I2C is 50Hz for the micro through the I2C port. The maximum sample rate for the USB will be 200Hz for the USB. You will need the firmware for version 3 and the new libraries to accomplish this.

I hope this helps,

Tim

So USB is not supported yet using the 2016 libraries currently available?

[slibert]

Originally Posted by cpapplefamily

So USB is not supported yet using the 2016 libraries currently available?

In 2016, USB was not supported by the FRC WPI Library (there was a bug in the underlying RoboRIO support). This particular bug has been resolved in the 2017 firmware which will be released on January 7.

I2C works very well, and works w/today's 2016 FRC libraries/RoboRIO firmware.

Summary:

- If using navX-Micro up with 2016 (old) FRC software/firware, use I2C at least until January 7
- If using the 2017 FRC beta software firmware, USB is available now

- scott

[GeeTwo]

The navX has both 5V and Vcc input voltage pins. The internal power for the navX is apparently 3.3V, based on the labeling of the power LED. While I cannot find this documented anywhere, it appears possible that the navX can be powered using 5V on the 5V pin, or using 3.3V on the Vcc pin. If I were planning to do this, I would join the navX forum and ask the engineers how and if you can power this $100 board using 3.3v.

[rlance]

Originally Posted by GeeTwo

The navX has both 5V and Vcc input voltage pins. The internal power for the navX is apparently 3.3V, based on the labeling of the power LED. While I cannot find this documented anywhere, it appears possible that the navX can be powered using 5V on the 5V pin, or using 3.3V on the Vcc pin. If I were planning to do this, I would join the navX forum and ask the engineers how and if you can power this $100 board using 3.3v.

On the navX web-site it states that the USB connection to the Roborio will provide the power needed for the navX-micro.

http://pdocs.kauailabs.com/navx-micr...-installation/

[slibert]

Originally Posted by GeeTwo

this $100 board

navX-Micro is $79 at the KauaiLabs store.

[slibert]

Originally Posted by cpapplefamily

Dose the 5v pin and the NavX Micro still NEED 5v?

The navX-Micro can be powered successfully even with 3.3V on the "5V" pin on the I2C connector, as long as it's really 3.3V.

The processor runs down to 1.7V, and the MPU-9250 runs down to 2.4V.

The navX-Micro has a voltage regulator with a max voltage drop of 725 mV.

So, when 3.3V is applied, the lowest output voltage will be 3.3 - .725 = 2.575.

The remaining headroom in the worst case is 2.575 - 2.4 = 175mV.

As long as you're OK w/that headroom, this configuration works.

NOTE: If you're getting power from the RoboRIO, be aware that if a stage 2 brownout occurs, the RoboRIO will remove power from the 3.3V "user" rail. For this reason, it's highly recommend to connect a USB cable to navX-Micro (if only as a backup power supply). navX-Micro - like navX-MXP - has a dual power supply input, and the RoboRIO USB ports provide 5VDC from a buck/boost regulator that continues generating current even during a stage 2 brownout. Please see the navX-Micro Best Practices for more details.