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'[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
Victor Fraenckel - The Windman
victorf ATSIGN windreader DOTcom
On Mon, May 09, 2005 at 07:26:07AM -0400, Vic Fraenckel wrote:
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.
"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
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