Problem with ADXL335

Using Arduino Sensors
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Dear all, my name is Kumpee, from Thailand. I am trying to build a simple GPS-aided INS using Arduino MEGA 2560, one 3-axis ADXL335 (3.3V), two of ADXRS (5V) and one MLX90609 (5V).

However, I got unstabled values as shown in the image. The upper part were the data from ADXL335 while the bottom were from the gryoscopes. I put them on my desktop so their output should be flat.

I tried to add delay(10) or delayMicroseconds(...) after each of analogRead but I got the similar results.

Could you please help me? ...Also, sorry for my English.

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2

The problem seems to be periodic. What is the period of the bursts?

3

Sorry, I didn't understand your question. But if you asked about sample rate, the data were sampled every ~0.01s (~100Hz).

Here were the other results. The first 60 seconds the device was stationary. After that, I rotated it 90 degrees around the horizontal axis.

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4

Every 5 seconds or so there seems to be a disturbance that lasts for about 1 second. Check the 3.3V power supply for disturbance also.

Is there something else in the circuit that might be causing the disturbance?

5

Here is the picture of my prototype.

6

I've removed the GPS receiver (SUP500F) from the board and those noises were disappeared. I don't know the reason. Anyway, I have to use the GPS receiver. So, how to prevent those noises if I have to connect the GPS receiver to the board again?

7

Try connecting the GPS with longer wires. If the problem comes back the GPS is probably creating noise on the power line. I'm not that familiar with noise reduction on power lines but I would guess that a combination of inductors and capacitors would filter out the noise.

8

Hi, johnwasser, I re-connected the GPS and the noises and the noises came back.

However, my problem is solved if I use external regulator (5V to 3.3V).

9

The onboard 3.3V supply on the Arduino cannot provide much current, only 50mA I think - usually this is enough for a sensor, but its certainly insufficient for a GPS receiver and sensors together - this causes the voltage to dip as the GPS receiver does its work.

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MarkT, thank you very much.

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