I asked a question before and got the answer.
I have responded to the results of the response, but have you received it?
I'll send it again.
I would appreciate your answer.
Regards,
＜question before＞
I use FDC2214EVM for a touch sensor of a robot.
From the terminal of the evaluation board,
I extend the sensor electrode pad with a cable and paste it inside the robot.
I confirm changes in capacitance when the electrode pad is touched by hand from outside
When measuring using [Data Streaming] of GUI
It shows 53pF when not touching the sensor, and 0.1 ~ 0.5pF capacitance increases when touching from outside.
My concern is that the sensor is reacting, but this 0.1 ~ 0.5pF is probably too small.
Can you tell me because I don't know if it's weak?
Regards
＜Conditions＞
Electrode size: 5mm x 10mm Electrode thickness:0.2~0.3mm
Robot material: Plastic Robot thickness: 0.2 ~ 0.3mm Cable length: 10cm
<Configuration,DataStreaming>
＜answer＞
Whether or not your target response is too small depends on your noise floor. You can measure your noise floor using the following steps:
- To measure the noise floor using an evaluation module, first download and open the Sensing Solutions GUI. For more detailed installation instructions, see the User’s Guide associated with the EVM.
- Once the GUI is open, navigate to the Configuration tab. Configure the RCOUNT setting so that the LDC or FDC device will sample the sensor frequency at the desired rate. Note: for non-default sensors, at this point the user will need to use an oscilloscope to verify that the sensor oscillation amplitude and the sensor frequency are within the acceptable range for the specific device, as specified in the datasheet. If the sensor oscillation amplitude is outside of the recommended range, the sensor drive current will need to be modified. Please see the Register Map in the datasheet for the registers that control the drive current settings. If the sensor oscillation frequency is outside of the frequency range supported by the device, either the inductor or the capacitor in the LC tank will need to be modified.
- Next, navigate to the Data Streaming tab. Click the “Start Streaming” button to begin the noise floor measurement. Ensure that the graph displays “Detected Sensor Frequency (MHz),” which is controlled by the drop down menu in the upper left corner. Click on the “Show Statistics” button to display the average and standard deviation of the data. Increase the number of decimals of the standard deviation until the last digit is rapidly changing. Use three times the standard deviation as the noise floor.
Kristin Jones
Current and Position Sensing
Applications Engineer
＜result to answer＞
Hi! Kristin
Thank you for answering kindly.
I checked step 1,2,or 3 you instructed.
Regarding Step 3 [Detected Sensor Frequency], the value is 5.332MHz when not touched, and the graph below shows when touched.
There are three questions.
① What does the noise floor mean?
Is this Detected Sensor Frequency related?
② If the standard deviation is 3 times, will the noise floor value be 0.033(0.011 × 3) based on this graph?
③ Where should I check if the SNR is 10?
I would appreciate your reply.
< 1:touch 2:no touch>
