I wanted to build a cheap accelerometer that met my dreams. It had to be under $20, and do the following things:
Interface with Internet by directly uploading into a buffer, so things were not lost when the earthquake hit.
Sufficient sensitivity to calibrate with distant earthquakes, by comparison with others.
I got as far as putting two adxl345's with a Raspberry Pi 2. It would get cheap with a raspi zero.
But the adxl345 isn't very sensitive. I got a factor of two increase by doubling and summing them.
Then the new Mcube accelerometers caught my eye, they should have been 16 times more sensitive. But, alas, the raspi can't work with them because they need i2c repeated starts. And that seems to be deficiency of the main computer chip in the raspi. I even consulted 'the smartest guy in the world' (who wrote wiringpi), and it seems hopeless.
I've made every search possible and I am totally defeated. But I did get to learn g++ along the way, and for me, many hours wasted on this, isn't really wasted.
They are always coming out with new tiny, cheap computers. Maybe next year I'll get it work. :)
ps. It seems the standard built-in i2c drivers are too complex. They take one call, and only do the standard i2c. A new approach for me will be using a simple bit-banging i2c driver written in c. I'll put that on the shelf for a while. :)