Accelerometer with Pic16f877

armando · Guest

I am new to using PIC microcontrollers and I currently have this project to determine the angle and acceleration using an ADXL202AE. This device sends out a DCM signal which can be decoded and interpreted using a microcontroller. I know a little bit of C, however I don't know where to start on actually obtaining the signal and interpreting it. Please help.

thnx,
Armando
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PCM programmer · Joined: 06 Sep 2003 Posts: 21708

:=I am new to using PIC microcontrollers and I currently have this project to determine the angle and acceleration using an ADXL202AE. This device sends out a DCM signal which can be decoded and interpreted using a microcontroller. I know a little bit of C, however I don't know where to start on actually obtaining the signal and interpreting it. Please help.
:=
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This chip outputs the acceleration as a PWM encoded signal.
So you need a method of measuring pulse widths. The PIC's
CCP module would be good for this. Look at the CCS example
file, EX_CCPMP.C. Do you have the CCS compiler ?
If not, that file is available online, here:
<a href="http://www.cc.puv.fi/~t0101190/projekti/source/Examples/" TARGET="_blank">http://www.cc.puv.fi/~t0101190/projekti/source/Examples/</a>

Analog Devices has a large number of appnotes on this device.
Go here, and look in the section on MEMS Technology:
<a href="http://www.analog.com/Analog_Root/sitePage/direct/applicationNotes/" TARGET="_blank">http://www.analog.com/Analog_Root/sitePage/direct/applicationNotes/</a>
Look at AN-604: Using the ADXL202 Duty Cycle Output

Also, AN-596, while not written for C, looks like it might
offer some useful tips.

Look at the CCS example file
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armando · Guest

Thanks alot. The two sites were very helpful.
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Kenny · Joined: 07 Sep 2003 Posts: 173 Location: Australia

<font face="Courier New" size=-1>:=I am new to using PIC microcontrollers and I currently have this project to determine the angle and acceleration using an ADXL202AE. This device sends out a DCM signal which can be decoded and interpreted using a microcontroller. I know a little bit of C, however I don't know where to start on actually obtaining the signal and interpreting it. Please help.
:=
:=thnx,
:=Armando

I have used a lot of these.
It is sometimes better to use the analog outputs at Xfilt and Yfilt into the PIC 10 bit A/D inputs. If low accelerations are to be measured then I use LM324 quad op-amps (one per axis) to boost the signal to suit the range of the A/D.
Spare op-amps are used to buffer an extra RC filter and restore the offset or zero adjustment.

The duty cycle modulator adds extra errors. It has a lower frequency response too but this is usually not a problem.

Another problem is separating tilt and acceleration. The acceleration response is reduced by the cosine of the angle to the axis and there will be a tilt component as well in the output if the device is not horizontal.

Good luck soldering them - the pads are under the package!
Regards
Kenny

</font>
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Acid · Guest

..Armando Do you know the chip for optical mouse..?
Bye

:=:=I am new to using PIC microcontrollers and I currently have this project to determine the angle and acceleration using an ADXL202AE. This device sends out a DCM signal which can be decoded and interpreted using a microcontroller. I know a little bit of C, however I don't know where to start on actually obtaining the signal and interpreting it. Please help.
:=:=
:=-----------------------------------------------------------
:=
:=This chip outputs the acceleration as a PWM encoded signal.
:=So you need a method of measuring pulse widths. The PIC's
:=CCP module would be good for this. Look at the CCS example
:=file, EX_CCPMP.C. Do you have the CCS compiler ?
:=If not, that file is available online, here:
:= <a href="http://www.cc.puv.fi/~t0101190/projekti/source/Examples/" TARGET="_blank"> <a href="http://www.cc.puv.fi/~t0101190/projekti/source/Examples/" TARGET="_blank">http://www.cc.puv.fi/~t0101190/projekti/source/Examples/</a></a>
:=
:=Analog Devices has a large number of appnotes on this device.
:=Go here, and look in the section on MEMS Technology:
:= <a href="http://www.analog.com/Analog_Root/sitePage/direct/applicationNotes/" TARGET="_blank"> <a href="http://www.analog.com/Analog_Root/sitePage/direct/applicationNotes/" TARGET="_blank">http://www.analog.com/Analog_Root/sitePage/direct/applicationNotes/</a></a>
:=Look at AN-604: Using the ADXL202 Duty Cycle Output
:=
:=Also, AN-596, while not written for C, looks like it might
:=offer some useful tips.
:=
:=Look at the CCS example file
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Bill Turnip · Guest

Armando -
I just interfaced this accelerometer to the 16f877 and 16f863 (or 4?) using the analog outputs (the PWM outputs dropped across a simple low-pass filter). It was pretty easy using ADCs.

Another question:
Is it possible to measure BOTH accelerometer axes at the same time (or close to it) using PWM outputs and the timers of the PIC?

Bill
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