Hi,
I am interfacing the sensor with FPGA to read the data in continuous mode, but the data read from the sensor is not changing after each time, its almost the same.
The scenario is same in trigger mode too. Can someone tell me y is this?
Is there any other configuration missing?
Regards
Athira
Athira,
Thanks for reaching out. It sounds like you have not enabled any magnetic channels. The device allows for custom configuration of the conversion pattern using MAG_CH_EN in the SENSOR_CONFIG register, and this is set to OFF by default:
Thanks,
Scott
If you see the image, the data is captured but if I am reading again, the value is not changing
Athira,
Absolutely. This step was to confirm you are successfully reading from the device. From here you should be set to start capturing more data to piece together for this purpose. Depending on the duration of travel for your magnet, you will want to either space out your samples, or increase the total number used for your calculations. In the case of the EVM, it defaults to 1000 samples, over a total timespan of about 75 ms. After a few tries, I was able to get a clean capture using a fixed number of samples on the EVM using your settings with the following plot
Here, I'm using a fairly strong magnet and moving the magnet pretty quickly by hand. I was able to capture most of my motion during the 75 ms interval.
If I move more slowly, the response shows much less change
From sample to sample the X output is only changing by 360 uT during the linear portion of the capture in the second plot.
You should also find that larger magnitude magnetic fields will produce greater magnitude changes with small position changes. This may be the result of using a stronger magnet or by placing the magnet existing magnet closer to the sensor. Had I used a smaller magnet further from the sensor, I would anticipate the change observed from point to point to be even smaller.
Thanks,
Scott
Hi Scott, I tried to use trigger to capture data every 500 us. I used cs pulse as the trigger. But the data I obtained is not as I expected.
Can you look into the picture below?
Hi Scott,
I am reading the x channel output with cs as trigger, and I used a data valid signal to capture the samples all together. The samples are changing but the change is abrupt.
Athira,
The output code is a 2s compliment to support +/- sensing range.
So with very low level input, or inputs that are changing between + and - values, it is likely to see a step between 00 and FF.
Also, in trigger mode, please be aware that with CS trigger, it will initialize and start the conversion when CS is low. you are leaving enough initialization time + conversion time before capturing outputs for each conversion
For two axis sampling in active trigger mode this should be about 85 us, which is well under your 500 us delay.
Thanks,
Scott
Athira,
There are two trigger modes that depend on the CS signal, and they behave differently:
For TRIGGER_MODE = 0b01, the trigger is defined to start as a low pulse. In this case there is no need for SPI transaction. The second option that relies on CS is TRIGGER_MODE = 0b00 to trigger using SPI. This is initiated using the CMD bits of the device.
When using this mode, CMD0 may be set so that the device will begin the next conversion at the completion of the write command; when CS is returned to the high state.
Thanks,
Scott
Hi Scott,
Now it is always like this. Crc error is always shown. I did not change anything but suddenly this happens.
Hi Scott,
I have the magnetic field values, but there are some jumps in the values which is not expected. The magnet is staying still. Please look the picture below.
Regards
Athira
Hi Scott,
In here there is no magnet present, but the waveform is like this. There is a jump 65523 to 32768(decimal)
Regards
Athira
Hi Scott,
But the shift is not happening when I place the magnet, its coming correct
Regards
Athira
Athira,
The output code is a 2s compliment format, are you doing any processing of the result to account for this?
With noise and offset, I would not be surprised to see the output vary from just above 0 to just below 2^16. For your case, it appears you have the just above 0 value offset by 2^15.
You might be able to test this by slowly moving the magnet above the sensor in this fashion:
Depending on how straight you are able to do this, you should be able to produce a plot similar to the green line. It might require rotating the magnet 90 degrees based on the axis you are reading. The green plot is the result of presenting both a positive and negative field during the motion. You should observe the positive region to all be greater than code 0, and the negative region to be less than 2^16. Unless you are saturating the inputs, you should not be near the midcode value.
Please check to make sure you don't see an issue with both polarities.
Thanks,
Scott
Hi Scott,
Yes I am doing the conversion. This is the converted result . I did not rotate the magnet, I just moved the magnet away. But the graph is good with magnet.
