LDC3114: Touch-Sensitive Switching Options

John La Grou

Part Number: LDC3114

Tool/software:

Hi. I have a requirement for a touch-sensitive switch. The touch pad must remain stationary, cannot move. The touch pad itself will be aluminum, and will be surrounded by an aluminum front panel. A PCB (coil trace?) sits underneath the touch pad metal (perhaps a 0.6" dia aluminum slug 0.3" long, not determined yet). Best I can tell, an inductive approach would be best. But it's not clear. In some app notes, it seems that the metal touch pad must move inward towards the coil. In other notes, it seems that the touch pad can be stationary. Thanks for any advice.

7 months ago

0 John Miller - Sensing 7 months ago

TI__Mastermind 40295 points

John,

Does the touch pad need to literally not move, or can it move a small amount that may be imperceptible to the user?
If it has to support no movement at all (and your requirements allow it) perhaps a capacitive touch sensor may be the best option.

regards,
John

0 John La Grou 7 months ago in reply to John Miller - Sensing

Intellectual 340 points

JM, it would make manufacturing so much easier if the "button" didn't move. I don't see a way to insulate the aluminum "button" from the actual aluminum front panel around it, so I'm not sure capacitive would work. We can always use a mechanical tact switch, but I would rather do something more unique. Are we out of luck?

0 John Miller - Sensing 7 months ago in reply to John La Grou

TI__Mastermind 40295 points

John,

Must the "button" be metal?
If it can be a non-conductive or non-ferrous material (like plastic), and not too thick, then a finger may act as enough of a conductor to result in a touch sensor.

The plot below shows the output of an off-the-shelf LDC1612 EVM (via the Sensing Solutions EVM GUI Tool v1.10.0) in terms of raw data versus time samples as a finger touched the EVM CH0 PCB sensor: raw data value drops as the finger touches the solder resist over the PCB coil.
It ranges from a max value of ~20,371,000 (w/o finger) to a min value of 20,120,000 (w/finger).

This experiment does not include any protective coating, which might have to be considered.
It also does not consider a finger covered by a glove of finger cot.

Regards,
John

0 John La Grou 7 months ago in reply to John Miller - Sensing

Intellectual 340 points

Thanks so much. I have some exploring to do.

0 John Miller - Sensing 7 months ago in reply to John La Grou

TI__Mastermind 40295 points

Ok John.

Please let me know if you have any questions.

Regards,
John

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LDC3114: Touch-Sensitive Switching Options