Accelerometers and pic

[Gerhard]

Hi.
I need to build a compass with 3 accelerometers on the three different axis and need some advice on which accelerometers would be ideal to use with a PIC16F886 or if i should go to another type of pic. I have read quite a bit on the net but there are so many models available. Please advice on this if someone has already used a certain meter that worked with the microchip pics and in ccs.

[Saratoga]

Yes.
I have this and work fine:
http://www.ccsinfo.com/forum/viewtopic.php?t=32753&highlight=wii
I made a VisualBasic pc program.The pic send data to serial port ,pc receive this data and draw the movement on the screen
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To Pic Or No To Pic

[mskala]

The answer will be different based on the type of interface used by the accelerometers. I use an analog, buffered, 2-D module from Dimension Engineering (they also sell a 3-D version), with PIC18 CPU's.

If you use an analog accelerometer, it is important that the output impedance is as good or better than the PIC datasheet says. That usually means an op-amp is involved. My products come with or without the accelerometer, so a module works well for me, but the module is really just the accelerometer part, follower op-amps, and filter caps on the outputs to set the bandwidth.

Mark S.

[Gerhard]

Thanks.
I have never used accelerometers and i am confused as to what type of analog accelerometer to use. The idea is to use 3 meters for the XYZ axis and implement this in such a way that the pic will via rs232 or some other format output the direction from 0 to 360 degrees to another unit. Maybe even display the orientation on a LCD. The acceleration will be measured and differentiated twice to find the displacement in a certain direction. The software will be designed around the basic analog input from the 3 meters but if you have some advice or reference to model numbers or circuits it would be appreciated.

[Gerhard]

I had a look at the 3 axis meter from dimension engineering and it looks like it will work. I just want to make sure that it will so if somebody has worked with that will i be able to make a compass with that one and display the value on a LCD that indicates the 0-360 degree bearing?

[kender]

You should be able to get away with 2-axis accelerometer and 2-axis magnetic sensor. One of the popular 2-axis accelerometers with analog output is Analog Devices ADXL203. It has a sensitivity of 1000mV/g, so it can be read by the PIC's A/D without additional amplification.

- Nick

P.S. You could also post your question here: http://tech.groups.yahoo.com/group/sensorforum
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Read the label, before opening a can of worms.

[mskala]

The need for amplification by itself is not really significant for devices like this, because in order to use it with the PIC you will need to put in an op-amp anyway to bring the output impedance down to the where the PIC needs it.

Mark S.

[Gerhard]

Thanks Kender.
I ordered the 3 axis acc meter from Dynamic engineering and now i am waiting for it. I also had a look at a digital compass available that uses hall effect magnetic sensing but due to the sensitivity of those magnetic devices to external magnetic fields i decided to go into the acc meter direction. Why would you recomend using 2 magnetic sensors as well?? I don't see why that is required if i need to build the compass. What would their purpose be?

[kender]