Botched
20Mar/120

Planning the New Board

Today was spent trawling through the mass of MEMS sensors that are now available, at which I am absolutely astonished! The chips on the market now are leagues ahead of their predecessors. For example, when I acquired the parts for my original board, the total came to around £250 for the five sensors, which you can now get in a single package for $15! Plus, the new ones have a much finer acuracy, have a built in adc with I2C output, and even a microprocessor to take the bulk of the sensor number crunching away from the main controller!

Currently it looks like I will be using the MPU-6050 by invensense. The gyroscope has a sensitivity of 131 LSB/°/s, compared to my previous ADXRS620 at around 6.8 LSB/°/s, while the accelerometer has a sensivity of 0.06 mg/LSB, up from 1.22 mg/LSB on my ADXL203's. Sadly the rms noise is only better by about a factor of 10 for the gyro, and 5 for the accelerometer, but I imagine these values will allow the craft to be so level that other effects such as wind and ground effect will have a larger affect on the drift.

The only two downsides are first the 256Hz built in low pass filter on both the gyro and accelerometer, and second the fact that it comes in a 4mm 24 pin QFN package. The LPF I hope will still allow for a fast enough update rate to maintain stability, and I *think* I should be able to manually solder the QFN package, probably with hot air or a hotplate. I just finished designing the required eagle symbol to mount the thing, and will now start building the rest of the circuit around it.

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