I am planning on interfacing the analog devices ADXL330 imems accelerometer to a PIC uC. I will be moving the sensor at a maximum rate of 18deg/s as a tilt sensor and will need .5 deg resolution. I have a few chioces to make and could use some insight to shorten my trial and error time.
1. The sensor has a ratiometric output. I can get 360 mV per g if i supply the sensor with 3.6V, or as low as 1.95mV/g @ 2V supply. 3.6 V seems to be the way to go for the max resolution. If I am missing anything, let me know.
2. Based on the output of the sensor 0-Vin for +/-3g. I will be using the center of this range (+/- 1g) I am thinking I should amplify only the Area I need and let the rest just saturate at the rails of the op amp (sound good?) This way i get the best resolution. So i take +/-90 deg or +/- 2g or 720mV and amplify to 5V to feed to my PICS ADC
3. So the order of the signal chain should be: sensor, gain amp, filter, uC, right?
4. Because the maximum rate of movement is (i think):
18 deg/s * 1g/90deg * 360mV/g = 72mV/s.
5. i should choose an op amp with a slew rate greater than 72mV/s
6. i should choose a low noise precision op amp,but not in-amp b/c the output from the sensor is not differential..
7. I should set my filter cutoff frequency at somewhere low (i was thinking 100 Hz, should I go lower?)
I am going to put a schematic on here in a few hours, if anyone could reply to let me know i am on the right track, I would appreciate it.
1. The sensor has a ratiometric output. I can get 360 mV per g if i supply the sensor with 3.6V, or as low as 1.95mV/g @ 2V supply. 3.6 V seems to be the way to go for the max resolution. If I am missing anything, let me know.
2. Based on the output of the sensor 0-Vin for +/-3g. I will be using the center of this range (+/- 1g) I am thinking I should amplify only the Area I need and let the rest just saturate at the rails of the op amp (sound good?) This way i get the best resolution. So i take +/-90 deg or +/- 2g or 720mV and amplify to 5V to feed to my PICS ADC
3. So the order of the signal chain should be: sensor, gain amp, filter, uC, right?
4. Because the maximum rate of movement is (i think):
18 deg/s * 1g/90deg * 360mV/g = 72mV/s.
5. i should choose an op amp with a slew rate greater than 72mV/s
6. i should choose a low noise precision op amp,but not in-amp b/c the output from the sensor is not differential..
7. I should set my filter cutoff frequency at somewhere low (i was thinking 100 Hz, should I go lower?)
I am going to put a schematic on here in a few hours, if anyone could reply to let me know i am on the right track, I would appreciate it.