PSoC 4 Capsense touchpad Low Baseline Reset Parameter

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
kc94
Level 1
Level 1
First reply posted First question asked First like given

Hello,

We are working with a touchpad (8 rows 7 columns at 9 bit resolution), running Capsense and are curious about the Low Baseline Reset Parameter. Namely, if our raw counts in the absence of a touch event are resting around a value of 450, what value should the Low Baseline Reset parameter be set to? What procedure should be carried out to determine that value?

The component datasheet lists a default value of 30, however if I understand the parameter correctly, our raw counts are never dropping that low and so the baseline is never updated. 

Additionally, what is a typical distribution of baselines across multiple sensors? Should it be concerning if they spread out over 50 counts? Or is a wide range normal as long as the diffcounts share similar values on a touch event?

Thank you in advance for any help! 

0 Likes
1 Solution
Hari
Moderator
Moderator
Moderator
750 replies posted 500 replies posted 250 solutions authored

Hi @kc94 

 

The low baseline reset parameter does not work on the absolute raw counts value. Instead, it works along with the negative noise threshold parameter. 

When the raw counts drop to a low value (could be due to the presence of a finger on startup or maybe some glitch in the power lines) the CapSense system compares this to the negative noise threshold. If the drop is greater than the negative noise threshold (if old rawcounts - new rawcounts > neg noise th) then the baseline is not updated. The baseline is held constant for low baseline reset number of cycles. If the value is set to 30, then for 30 cycles, the baseline is not updated and then it is updated to the new value. 

Therefore, the low baseline reset is independent of the raw counts or drop in raw counts. 

Hari_0-1631076516496.png

Here, the blue line shows the rawcounts and the yellow line is the baseline. The baseline is only updated after 30 scan cycles (since the low baseline reset is set to 30).

 

Should it be concerning if they spread out over 50 counts? Or is a wide range normal as long as the diffcounts share similar values on a touch event?

A difference of 50 between raw counts is alright. The performance will be good as long as they share similar difference counts value. 

 

Best regards, 
Hari

View solution in original post

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

Hi @kc94 

 

The low baseline reset parameter does not work on the absolute raw counts value. Instead, it works along with the negative noise threshold parameter. 

When the raw counts drop to a low value (could be due to the presence of a finger on startup or maybe some glitch in the power lines) the CapSense system compares this to the negative noise threshold. If the drop is greater than the negative noise threshold (if old rawcounts - new rawcounts > neg noise th) then the baseline is not updated. The baseline is held constant for low baseline reset number of cycles. If the value is set to 30, then for 30 cycles, the baseline is not updated and then it is updated to the new value. 

Therefore, the low baseline reset is independent of the raw counts or drop in raw counts. 

Hari_0-1631076516496.png

Here, the blue line shows the rawcounts and the yellow line is the baseline. The baseline is only updated after 30 scan cycles (since the low baseline reset is set to 30).

 

Should it be concerning if they spread out over 50 counts? Or is a wide range normal as long as the diffcounts share similar values on a touch event?

A difference of 50 between raw counts is alright. The performance will be good as long as they share similar difference counts value. 

 

Best regards, 
Hari