ADXL202 calibration

Archiver

Hi. I have 4 ADXL202 evalution boards that I'm using to sense degree of
tilt with. I've noticed that they give different readings at the exact same
angle. I suspect this is due to variance in the resistor used to set the
PWM period (Rset), but I wanted to put the question to the group before I
start unsoldering components on the board to check.

Any ideas?

Thanks

Mark Allen

Archiver

Mark,

Yes, this is the likely source of variance, but note that sensitivity of
each individual accelerometer varies with position. ADXL202e data
sheet, page 11: "An accelerometer is most sensitive to tilt when its
sensitive axis is perpendicular to the force of gravity ... and least
sensitive when oriented on axis to gravity." Also recommended (page 12)
is to calibrate each accelerometer by making measurements at +1g and
-1g, subtracting them and divide by 2g. Store the resulting sensitivity
value as a scale factor and offset in EEPROM of a stamp or PIC.

Dennis

---

Original Message

---

From: mark allen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=Jbsq3O3Bie2obdcmx43XmF6guYVYdEIuPSCPbbBi37mMzEF7f6yGkwCAYI5h_O12kFqR65CC0PzuGSTP]mallen@c...[/url
Sent: Wednesday, August 28, 2002 9:44 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] ADXL202 calibration


Hi. I have 4 ADXL202 evalution boards that I'm using to sense degree of
tilt with. I've noticed that they give different readings at the exact
same
angle. I suspect this is due to variance in the resistor used to set the

PWM period (Rset), but I wanted to put the question to the group before
I
start unsoldering components on the board to check.

Any ideas?

Thanks

Mark Allen


To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.


Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/

Archiver

The data sheets indicate the 202 will operate from ~ 3 to 5V. One of my
channels generates pulse widths that are independent of Vcc, but the other
channel pulse width changes significantly within the "legal" range of Vcc.
The data sheets do not address Vcc sensitivity. Has anyone else observed
this effect? Aside from this, the IC seems OK.

Thanks,
Ray McArthur

Archiver

It is sort of like using a DAC (Digital analog converter) or ADC (analog to
digital converter), they are very sensitive to changes in the VCC and noise
on VCC as well. The better your VCC input to the device the better it's
readings would be.
This is a common problem with all of these kinds devices not just the 202.

---

Original Message

---

From: Ray McArthur [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ul5S2fUTPgOgu1s8inb7-V2OGmoxbU3aHEkFpgVianDfmlpggkBVsbmrHs7_alwRJVNiwxU8izlbk7_I2Wc]rjmca@u...[/url
Sent: Wednesday, August 28, 2002 8:55 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] ADXL202 calibration


The data sheets indicate the 202 will operate from ~ 3 to 5V. One of my
channels generates pulse widths that are independent of Vcc, but the other
channel pulse width changes significantly within the "legal" range of Vcc.
The data sheets do not address Vcc sensitivity. Has anyone else observed
this effect? Aside from this, the IC seems OK.

Thanks,
Ray McArthur


To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.


Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/