TSS keypad with very low delta values

[francescoprospe]

Hi all,

I'm trying to improve the delta values for my custom board featuring S08PT32 (with 6 electrodes). Currently delta values are around 5.

Although a bit outdated, following the TSI tuning online application note (on the Freescale Technical Information Center),

it seems that the variables to be changed are:

#define TSS_TSI_PS_LOW_LIMIT        0  /* Low Limit of External OSC Prescaler register value for TSI auto-calibration */

#define TSS_TSI_PS_HIGH_LIMIT        7  /* High Limit of External OSC Prescaler regiters value for TSI auto-calibration *

I tried changing such values together with

#define TSS_TSI_EXTCHRG_LOW_LIMIT  0  /* Low Limit of External OSC Charge Current register value for TSI auto-calibration */

#define TSS_TSI_EXTCHRG_HIGH_LIMIT  7  /* High Limit of External OSC Charge Current register value for TSI auto-calibration */

and the TSS_TSI_RESOLUTION (currently 11).

but with no effect.

To improve delta, I could use signal multiplying but I don't see it as a good way to go.

Is there any way I am missing to improve delta values to be around 20-70 (as suggested in the application note previously pointed out) ?

Best regards,

Francesco Prosperi

[moravcik]

Hello Francesco,

The main parameter which can increase TSI signal level is, as you mentioned, TSS_TSI_RESOLUTION. You can try to increase also number of TSI samples by System_NSamples_Register, but I think that reason of your small delta can be more on hardware side. You have probably very small size of electrode, or very big thickness of plastic cover material, or there is GND area which decreasing sensitivity. Please read AN3863, on this link http://cache.freescale.com/files/sensors/doc/app_note/AN3863.pdf

Let me know if it helped

Best Regards

Peter Moravcik

TSS SW Team

[francescoprospe]

Hi Peter, thanks for your reply.

I've tried increseasing TSS_TSI_RESOLUTION but with no significant gain. In your opinion, is too silly to use the SIGNAL_MULTIPLIER functionality to obtain "higher" values ?

As you pointed out, my small deltas could come from a very constrained hardware environment (plastic, schematic, and so on) but there's basically nothing to do about it (right now).

Best regards,

Francesco