Post by thread:[EE] ADC help/advice needed

I am in need of some advice and help on A/D converters. I have a device, an accelerometer (Kionix KXM52-1050 tri-axis) whose output is a voltage proportional to the acceleration being sensed. The specs for this device are: Range g ±2.0 Sensitivity 2 mV/g 660 @3.3V 0g Offset vs. Temp.mV ±100 Over temp range°C -40 to 85 Sensitivity vs. Temp % ±2.0 typical (±3.0 max) Over temp range Span mV ±1320 @ 3.3 V Noise 35 (x and y) 65 (z) typical Bandwidth Hz (0 to 3000 max (x and y axis) or (0 to 1500 max (z axis)) -3dB Output Resistance Ohms 32K typical Non-Linearity % of FS ±0.1 typical (±0.5 max) Ratiometric Error % ±1.0 typical (±1.5 max) Cross-axis Sensitivity % ±2.0 typical (±3.0 max) Power Supply V 2.5 to 5.5 mA 1.5 typical (1.8 max) Current draw @ 3.3V µA <10 Shutdown pin connected to GND ms 1.6 Power-up time @ 500 Hz 6 If I were to interface this directly to a PIC with a 10 bit ADC would this be a reasonable solution? Would I get good conversion accuracy. Would I need to make provisions to shift the span from +/- 1320 mV to 0 to 5 volts. If this is a better way, could you advise me as to how to do this. Being a relatively new device, there is very little information or application notes available. I have done a Google search so I know this. This sort of application is new to me and any enlightenment will be greatly appreciated. TIA Vic ________________________________________________________ Victor Fraenckel - The Windman victorf ATSIGN windreader DOTcom KC2GUI

Hi Vic, On Mon, May 09, 2005 at 07:26:07AM -0400, Vic Fraenckel wrote: {Quote hidden}> Range g ?2.0 > Sensitivity 2 mV/g 660 @3.3V > 0g Offset vs. Temp.mV ?100 Over temp range?C -40 to 85 > Sensitivity vs. Temp % ?2.0 typical (?3.0 max) Over temp range > Span mV ?1320 @ 3.3 V > Noise 35 (x and y) 65 (z) typical > Bandwidth Hz (0 to 3000 max (x and y axis) or (0 to 1500 max (z axis)) -3dB > > Output Resistance Ohms 32K typical > Non-Linearity % of FS ?0.1 typical (?0.5 max) > Ratiometric Error % ?1.0 typical (?1.5 max) > Cross-axis Sensitivity % ?2.0 typical (?3.0 max) > Power Supply V 2.5 to 5.5 > mA 1.5 typical (1.8 max) Current draw @ 3.3V > ?A <10 Shutdown pin connected to GND > ms 1.6 Power-up time @ 500 Hz 6 > > If I were to interface this directly to a PIC with a 10 bit ADC would this > be a > reasonable solution? Would I get good conversion accuracy. Would I need to > make > provisions to shift the span from +/- 1320 mV to 0 to 5 volts. If this is a > better way, could you advise me as to how to do this. You will need at least a buffer amp. The A/D source impedance needs to be 10k or less and the senser's impedance is 32k. Also the minimum A/D reference voltage is 2.5 (2.2 with accuracy loss) so for a full scale 10-bit result you will need to scale your input up some amount. As far as converstion accuracy goes the PIC's A/D converter is rated at -+1 LSB at Vref = 5.0V. Well, this is about the limit of my knowledge! I hope others can reply. Matthew. -- "I am a Liberal because I prefer progress to stagnation; because I place the happiness of the many above the privileges of the few; and because I believe that disasterous revolutions are best averted by timely reforms." -- George Osborne Morgan