equivalent
Newbie level 4
You seem to be making heavy weather of this...
So you'll need at least a 10ksps 16 bit a/d, for one channel (and you could use a 30 ksps a/d multiplexed around 3 channels, if you really wanted to).
halls wrote:
The trouble is that sigma-delta adc tend to be accurate, but slow. The LTC2487 mentioned earlier is about a thousand times too slow for the application, depending on whether you sample one ch or several.
Note that you can get semiconductor accelerometers which interface directly but don't quite meet your requirements (but are a whole lot closer than a factor of 1000 off). In general, semiconductor accelerometers are cheap and have integrated electronics, which allows the manufacturer to trim them in production. These are designed for things like airbags and the Wiimote/iPhone, etc.
In general, any time that you design things this way around (select some of the parts without taking into account all of the specification), you'll find that the parts of the specification that you didn't take into account turn out to be problematic/expensive. So, if you were designing with an accelerometer with an analogue interface, selecting a board with a suitable ADC would have been a good idea. If, on the other hand, you were designing with a digitally interfaced accel, then having the appropriate serial interfaces would be vital.
On the other hand a AD7655 looks good; the data sheet I have seen is for a 4-ch part and can be selected for serial or parallel interface; its succesive approximation, precise enough and fast enough (good). I'm not quite clear how the serial interface works as it claims to be compatible with several different standards including SPI and I'm not sure how you select the one you want.
sorenriis said:
So you'll need at least a 10ksps 16 bit a/d, for one channel (and you could use a 30 ksps a/d multiplexed around 3 channels, if you really wanted to).
halls wrote:
The trouble is that sigma-delta adc tend to be accurate, but slow. The LTC2487 mentioned earlier is about a thousand times too slow for the application, depending on whether you sample one ch or several.
Note that you can get semiconductor accelerometers which interface directly but don't quite meet your requirements (but are a whole lot closer than a factor of 1000 off). In general, semiconductor accelerometers are cheap and have integrated electronics, which allows the manufacturer to trim them in production. These are designed for things like airbags and the Wiimote/iPhone, etc.
In general, any time that you design things this way around (select some of the parts without taking into account all of the specification), you'll find that the parts of the specification that you didn't take into account turn out to be problematic/expensive. So, if you were designing with an accelerometer with an analogue interface, selecting a board with a suitable ADC would have been a good idea. If, on the other hand, you were designing with a digitally interfaced accel, then having the appropriate serial interfaces would be vital.
On the other hand a AD7655 looks good; the data sheet I have seen is for a 4-ch part and can be selected for serial or parallel interface; its succesive approximation, precise enough and fast enough (good). I'm not quite clear how the serial interface works as it claims to be compatible with several different standards including SPI and I'm not sure how you select the one you want.
