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PSoC 4 MCU

New Contributor

We have a home automation product that is using the CY8CMBR3106S.  It is installed in the wall and is mains referenced.

When we debug the proximity detection using a CY3280-MBR3, we notice a 1.6Hz waveform that is causing false triggers.  We know it is somehow specific to the installation.  It is not an issue everywhere, and all of the units work perfectly out of the wall.

So far the immediate solution has been to reduce the resolution of the Proximity detection and in so doing reduce the sensitivity.

I'm wondering if someone has experienced this and is able to help us find a better solution.

The hardware is configured as follows:

1 x slider - SLD10-SLD14 

1 x button - CS4

proximity detection - PS0

Driven Shield - CS5

Attachments are as follows:

- Schematics of the sensor

- Output that is causing false proximity detections.

- PCB top and bottom layers showing shield ring, Proximity ring and shield Hatch, as well as CY8CMBR3106 layout.

Thanks in advance for your response.

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1 Solution
Moderator
Moderator

Hi stdi_2473871​,

1. The MBR3 has an internal regulator that provides stable internal voltage of 1.8 V for core operation.

But the CapSense system charges and discharges the sensor directly using the VDDD supply and the maximum allowed ripple is as follows:

pastedImage_0.png

Please probe the VDD supply and see if there the ripples is within this range.

2. This effect also could be due to some close by trace interfering with the CapSense sensor trace. Please ensure that you have at least 14 mil mil air gap between capsense trace and other traces . It is highly recommended to have a ground trace between capsense trace and other signal traces with 10 to 14 mil air gap between capsense trace and ground trace.

3. We suggest you to connect the shield ring to ground and check the performance again. You can have higher resolutions for higher sensitivity in that case.

4. What is the prox loop diameter and expected proximity distance. We recommend having at least diagonal of the loop equal to the required proximity distance.

5. We highly recommend you to use only PSoC 4S devices (4000S, 4100 S and 4100 S plus) for newer designs since it has the latest generation of CapSense in it and it is also programmable. MBR3 is only targeted for small applications with less complex designs.

6. By other sensors,  I meant the other CapSense sensors connected to MBR3 device.

Regards,

Bragadeesh

Regards,
Bragadeesh

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3 Replies
Moderator
Moderator

Hi stdi_2473871​,

1. Please use 330 series resistors on I2C lines for better EMC performance.

2. Is the ring inside the proximity loop connected to shield or ground? We usually recommend to place a ground ring near proximity sensor for better noise immunity

3. This look like a supply issue. Can you probe the power supply pin and check if you are seeing this 1. 65 Hz frequency component

4. Do the other sensors in your design show a similar frequency component in the waveform.

5. Was the issue reproducible with a stable bench top power supply?

6. Have you enabled firmware filters?

7. Probe the sensor pin and check if you are observing this component in the charging and discharging waveform as well.

If possible please share the complete schematic (showing the power supply filters) and the layout.

Regards,

Bragadeesh

Regards,
Bragadeesh
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New Contributor

Thank you Bragadeesh for your response.

A few things there for me to try.  Unfortunately, we are unable to replicate the problem at the office, so this will make it a little more challenging/time consuming, but I will work towards getting your questions answered over the next few days.

1. Please use 330 series resistors on I2C lines for better EMC performance.

Okay, I will try this and see if it makes any improvement.

2. Is the ring inside the proximity loop connected to shield or ground? We usually recommend to place a ground ring near proximity sensor for better noise immunity

The inside guard is connected to the shield.  This was in keeping with CY8CKIT-024 which can optionally connect the Guard ring and Hatch to shield or GND.  We also have the option to connect to shield or ground, but we have found that the shield gives better performance.

3. This look like a supply issue. Can you probe the power supply pin and check if you are seeing this 1. 65 Hz frequency component

The supply looks good, but I will check it again tomorrow.

Isn't the CY8CMBR responsible for generating its own 1.8V supply for the 'core and capacitive sensing circuits'.  I would expect it to attenuate the noise and therefore shouldn't be susceptible to noise from the VDD power supply.  On our hardware, the CY8CMBR is indeed sharing the 3.3V supply with other digital electronics.

Test 5 should help confirm either way.

4. Do the other sensors in your design show a similar frequency component in the waveform.

There is one other sensor (temperature sensor). We cannot tell if it is also suffering from this issue.

5. Was the issue reproducible with a stable bench top power supply?

It will take some time, but I have an idea about how I can do this.

6. Have you enabled firmware filters?

Both IIR and Median filters are active.Screen Shot 2020-03-24 at 10.39.12 pm.png

Screen Shot 2020-03-24 at 10.39.34 pm.png

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Moderator
Moderator

Hi stdi_2473871​,

1. The MBR3 has an internal regulator that provides stable internal voltage of 1.8 V for core operation.

But the CapSense system charges and discharges the sensor directly using the VDDD supply and the maximum allowed ripple is as follows:

pastedImage_0.png

Please probe the VDD supply and see if there the ripples is within this range.

2. This effect also could be due to some close by trace interfering with the CapSense sensor trace. Please ensure that you have at least 14 mil mil air gap between capsense trace and other traces . It is highly recommended to have a ground trace between capsense trace and other signal traces with 10 to 14 mil air gap between capsense trace and ground trace.

3. We suggest you to connect the shield ring to ground and check the performance again. You can have higher resolutions for higher sensitivity in that case.

4. What is the prox loop diameter and expected proximity distance. We recommend having at least diagonal of the loop equal to the required proximity distance.

5. We highly recommend you to use only PSoC 4S devices (4000S, 4100 S and 4100 S plus) for newer designs since it has the latest generation of CapSense in it and it is also programmable. MBR3 is only targeted for small applications with less complex designs.

6. By other sensors,  I meant the other CapSense sensors connected to MBR3 device.

Regards,

Bragadeesh

Regards,
Bragadeesh

View solution in original post

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