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CAPSENSE™ & MagSense

spyhabs
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Hello,

 

I have a question related to the proximity consumption.  I noticed that the proximity consumption is similar to scan 12 buttons at 200 ms.  Is it possible to find a spec somewhere describing proximity current?

 

My board with 1 button scan only, I measured ~40 uA.

Board with 12 buttons, no proximity enabled : ~110 uA.

Board with 12 buttons, proximity CS1 activated : ~105 uA.

So, I'd preferred to have consumption with around 40uA like one button.  It's why I am confused about this... bad configuration?

 

Thanks

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Hari
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Hi @spyhabs 

 

The increase in current consumption is expected as the sensing time is increased when more sensors are present. Note that for button sensors, the MBR3 can assign a lower resolution, but for proximity sensors, the sensor always scans at 16 bit resolution. Therefore, the time the CapSense sensors are scanned increases and thereby, the current consumed also increases. 

 

You can check the approximate current consumption by entering the relevant parameters in the Design Toolbox which you can obtain by going to Configurations > Open design toolbox in EZ-Click software.

 

Best regards, 
Hari

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Hari
Moderator
Moderator 750 replies posted 500 replies posted 250 solutions authored
Moderator

Hi @spyhabs 

 

The increase in current consumption is expected as the sensing time is increased when more sensors are present. Note that for button sensors, the MBR3 can assign a lower resolution, but for proximity sensors, the sensor always scans at 16 bit resolution. Therefore, the time the CapSense sensors are scanned increases and thereby, the current consumed also increases. 

 

You can check the approximate current consumption by entering the relevant parameters in the Design Toolbox which you can obtain by going to Configurations > Open design toolbox in EZ-Click software.

 

Best regards, 
Hari

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spyhabs
Level 1
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Thanks for your reply Hari,

An other point... in order to save power,  is it a good design to activate only one button.  So the customer can press the button to wake up the host.  And then, configure the keypad to activate all buttons for a few seconds.  Finally, re-configure the keypad to have one button scan when the host returns in sleep. 

I see in the datasheet that we need to save registers in flash and then, do a reset each time.  And the flash endurance is around 100K write.    

Activate one sensor only has a very low consumption and I like this level.  The sleep consumption is very important in this product to have a long battery life.

Best regards,

Christian 

 

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Hari
Moderator
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Hi @spyhabs 

 

You can use the wake-on-approach feature of the MBR3 which only scans the proximity sensor in a loop, thereby saving power. Only if a hand approaches the sensor, it goes to look for touch mode and scans all the sensors. 

Hari_0-1620823575802.png

 

 


I see in the datasheet that we need to save registers in flash and then, do a reset each time.  And the flash endurance is around 100K write.   



This is correct. However, the flash writes are required only if you change the configuration and is not needed in normal CapSense execution flow. 

 

Best regards, 
Hari

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spyhabs
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Hello Hari,

 

I configured 2 different versions.  

1) Look For Proximity Mode (Wake-On approach) and 12 key sensors (200 ms polling)

My board consumption is ~100 uA @ 4.5V (Average) 

2) Look for Touch Mode only with 12 sensors for keys (200 ms polling)

My board consumption is ~110 uA @ 4.5V (Average)

 

So, the consumption with proximity activated is very high.  We check the consumption with a scope and the proximity process duration is around 7.8 ms at each 200 ms.  We measured around 3.3 mA when the proximity is activated. 

So, is it possible to decrease the proximity consumption?  Actually, we use 16-bits for the resolution and it's the best we can to have about the proximity detection.   

The proximity distance is not very good. Only 2, 3 centimeters…   Our target was ~ 10 centimeters.  But it's an other issue.  I want focusing on consumption first.

Thanks for your help!  I appreciate it.

 

Christian

 

 

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Hari
Moderator
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Hi Christian, 

 

Unfortunately, the proximity sensing resolution cannot be decreased. The hardware is configured such that it always scans with 16 bits resolution and it is the resolution that determines the scan time. 

 

You could increase the polling time so that it scans less frequently.

 

Regarding the sensing distance, Please let me know the type of sensor that you are using. We recommend using a loop sensor, of diameter equal to the sensing distance. It is also recommended to use shield for reducing the Cp for better proximity distance.

 

Best regards, 
Hari

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spyhabs
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Hello Hari,

 

Here is more information:

1) We use a shield for the water tolerance but not yet tested.

2) the proximity is a rectangular sensor (3 mm x 47 mm).  There is no space to have a loop sensor.  Also, the proximity sensor is not centered but located at the right of the keypad.  

With these conditions, we can have 2 or 3 cms only.  The CY8CMBR3116 is interfaced directly with our microcontroller.  We don't use any cypress microcontroller to connect to it.  

 

Thanks

 

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Hari
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Hi @spyhabs 

 

3 x 47 mm is a very big sensor and without using shield, the Cp of this sensor would be very high. This would explain the low sensing distance. 

Note that we recommend a loop sensor so that the Cp is small - enabling the sensors to be more sensitive. 

 

Also note that for any X x Y sensor, the distance it can measure is the diagonal distance, which in this case would be around 5cm. Therefore, with the loop sensor and shield, we would still be looking at 5 cm of sensing distance. With firmware filters such as ALP, it would be possible to sense a larger distance but note that this comes at a cost of reduced responsiveness and increased power consumption. 

 

Best regards, 
Hari

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spyhabs
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Hello Hari,

Actually, we don't have any success for the distance.  It doesn't detect the finger, I need to use whole hand in front of the reader and low distance... < 3 cms.  I would like to have min 5 cms and ideally 10 cms.  Also, the consumption is still very important.  

 

It's a nice technology but it's hard to get the right parameters to have low consumption, high distance detection.

 

Thanks a lot!   

 

 

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Hari
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Moderator 750 replies posted 500 replies posted 250 solutions authored
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Hi @spyhabs 

 

The issue here is the high Cp of the sensors. I would highly recommend trying out the shield hatch around proximity for a significant change in performance initially. If you still wish to extend the range, you can use a loop sensor and further, Ez-Click provides to option to enable ALP filters which are also excellent in providing responsiveness with suppressed noise. 

 

Best regards, 
Hari

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