How to lower the baseline levels of the raw count in CY8CMBR3108 design

[shhe_3888866]

Hello,

I'm using the CY8CMBR3108 with my own design of sensor, I'm trying to design some specific sensors and I'm facing a problem.

My initial signal with a small sensor, or no sensor is around 45000 , in 16 bits resolution. When I add different types of sensors, I get a result of over 65000 in raw count, this signal is saturated and clipped, and I get no measurement.

Is there a way, a configuration issue I can use, or any other method to reduce the baseline raw count level  when there is no signal, or no body near the sensor ?

I use the CapSense device as a proximity sensor, I need to detect human presence nearby, in a range of about 50 cm, and I can enlarge sensor size to a diameter of about 30cm, or a little larger.

Is there a method for configuration the sensitivity of the device ?

Thank you,

[BragadeeshV · Accepted solution]

Hi shhe_3888866​,

MBR3 device can detect (tested) up to 30 cm distance with the ALP filter enabled.

If you want to detect up to 30 cm, then you  need to have a minimum of 15 cm loop diagonal with the ALP filter enabled.

The Cp of the sensor needs to be between 5 to 45 pF.

Can you measure the Cp of the sensor using ez-click and check if it between the range 5 to 45 pF?

It may not be possible to detect 50 cm using CapSense devices. (Not validated)

The proximity distance increases if the Cp of the sensor decreases. Therefore it is recommended to use make sure that there is no conductive floating objects near the proximity sensor. There should not be any ground near the sensor (except a ground ring around the sensor for noise immunity). It is recommended to drive shield for the hatch pattern (if any) to reduce Cp of the sensor.

Since MBR3 uses SmartSense, you may not be able to use this device, if the Cp is greater than 45 pF.

We highly recommend using latest gen CapSense devices such PSoC 4000S, 4100S and 4100S plus, that supports upto 200 pF parasitic capacitance. Since ALP filter support is available only for older capsense components (v2.0), so you have to use this for higher distances.

The MBR3 device will set the no touch raw counts (called baselines) to 85 % of the max raw count 0.85 * 2^16 (~55705 +/- 10%). If you do not observe this, then it means the auto-calibration has failed. This could mean the sensor Cp is too high.

Regards,

Bragadeesh