Lab board for 3-axis accelerometer and 3-axis digital compass from mobile phone.
Features – accelerometer and compass breakout board
- Breakout connector for important signals
- Flip chip connection for BGA and LGA components
- Single sided PCB
Features – microprocessor lab board (optional – same as above, but with microprocessor and LDO)
- SMD microprocessor (PIC 16F628) with ICSP connector
- On board 3v LDO
- Measure wires for VCC, GND, SDA & SCL
- Status LEDs
I wanted to play around with 3-axis accelerometer and 3-axis digital compass that can be found in mobile phones. I have quite good access to these components since they are used in mobile phones like Huawei 8300. The biggest problem with them is that they have quite small packages (LGA and QFN). I designed two circuit boards, one breakout board for various microprocessors, like Arduino and one board for a PIC microprocessor. The boards do not require solder mask or IR oven. This is how they were done:
- Design the PCB
The PCB was designed and routed in Rhino, using this method.
- Make the PCB
The PCB was prepared and milled using HTML CAM.
- Desolder components
I used a hot air soldering iron to remove the two sensor chips from a U8300 Android Smartphone.
- Solder the tricky components
The accelerometer and digital compass was glued upside down on the PCB with a tiny drop of quick glue. Then they were bonded to the surrounding pads using thin copper wire and a soldering iron with a small tip under a microscope.
- Solder the rest of the components
The other components are no match after the previous stage. All are SMD except the connectors.
- Write program
I wrote a small test program in PIC assembler that communicates with the sensors over I2C (bit banging the protocol). The program is still at a very early stage (hello world level) use it at own risk…
- Upload program and test the board
A pickit2 programmer was used to upload the compiled code. The board is powered thru the same programmer and the serial interface also connected to the ISCP, allowing debug data to be sent to a terminal window on the PC.
Dimensions [mm]: 50 x 35.6
0.1 First version of PCB
0.2 Fixed LDO routing
0.3 added switch to select 3/5v for the PIC (see photo)
0.4 rewired RX and TX lines with extra cables (see photo)
Future Updated SW versions
Rhino project file (2D lines)
2D export (.svg) – breakout and lab board
Microprocessor program – PIC assembler (work in progress)
Datasheet ADXL345 (3-axis accelerometer)
Datasheet AK8973 (3-axis digital compass)
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