Freerunner Navigation Board
Note: a second generation version has been announced that will add a 3D Gyroscope and a Barometer sensor: http://lists.openmoko.org/nabble.html#nabble-f1954
The Freerunner Navigation Board is a small PCB which can be mounted inside the case to extend the Freerunner with additional Hardware. The Board contains the triaxial digital compass chip HMC5843 from Honeywell and two gyroscope chips from InvenSense (IDG650, ISZ650) to provide a triaxial gyroscope solution.
The board can be connected to the I2C bus which is available on testpads around the debug connector.
The compass chip is directly connected to the I2C bus. The gyroscopes have analog outputs which are digitized using the 16-bit A/D converter ADS1115 from Texas Instruments.
Additional features which are planned but are not implemented yet: The board contains the footprint to add an additional MSP430 microcontroller from TI. It would be used to control the offset compensation features of the gyroscopes, read their internal temperature sensors and switch them off when not used. Latter can actually be done using a GPIO line which is available at a testpoint H-TP1516.
|Top side: a voltage regulator and two gyroscopes from InvenSense|
|Bottom side: the digital compass chip, space for a MSP430 microcontroller and two ADCs.|
|Make sure that the shield or the GPS connector can't cause short circuits.|
|Insert the board into the empty space under the GPS connector. It fits exactly.|
|Solder the I2C-Wires to the testpoints at the debug connector. Refer to I2C for the pinout. The white wire is used to control the power supply of the gyroscopes. It connects to H-TP1516, or directly to 3.3V if this functionality is not needed. Power can be stolen from the AUX-Switch or, in this case, from the decoupling capacitor of the accelerometer. This power source will be disabled when the device suspends.|
|Reassemble the phone and stuff the remaining wires into the free space under the main PCB.|
Right now, this additional hardware is not supported out of the box, but there are some pieces of software available to demonstrate that the hardware actually works.
Hardware drivers are available from gitorious.
A kernel driver is available to control the HMC5843 digital compass through sysfs entries. Vala hackers can use a vala library for easier access.
The Gyroscopes need a driver for the ADCs which can be downloaded from the ADS1115 repository. Besides the kernel module, these chips can be accessed from userspace using the i2c-dev driver and a userspace library. Vala bindings are available.
End user software
The monitor has been developed in order to easily add arbitrary sensors as sources. The monitor uses GTK and Cairo for drawing the values and right now the redrawing speed is acceptable on the GTA02. Right now auto-scaling etc. can not be applied for this reason.
Except for the above mentioned sensors there have been written plugins for:
- LIS302DL accelerometers (the ones included in our devices)
- BMP085 pressure sensor
- Senserion SHT21 humidity sensor
- Logged input from text file
- Streaming over TCP sensor data from the freerunner to your desktop
This is a screenshot of the application monitoring the X and Y gyro-axis as well as the X-axis of the digital compass included in the navigation board:
Here is a screenshot of the available sensors that SensMon is currently able to monitor:
The sensor monitor has been tested on SHR unstable and Debian sid only.
Extending the Hardware extension
Since each of the two ADC chips provides two channels and the gyroscope solution needs only three out of four, one channel is free for use. A wire can be soldered onto a tiny testpad or directly to the pin on the chip.
Possible use cases
- connect an ambient light sensor
- other cool stuff
- Using the navigation board together with the I2C Pressure Sensor results in a not working NOR uboot. Everything else seems to be alright. If you have any clue what's happening, please tell me!
- A few features of the gyroscopes such as "auto zero" or the integrated temperature sensor can not be used without an additional microcontroller.