TN0235

FAAQs and answers

Doc ID 17218 Rev 1

3/9

2

FAAQs and answers

2.1

How does human detection work?

The human detection is made using a well-known and proven technology called “capacitive

charge transfer”. It is based on the fact that the human body acts as a conductive object.

Basically, small changes in the capacitance of an electrode, which is affected by human

presence, are measured. The electrode is usually made of a copper plate behind a

dielectric.

To measure changes in the electrode capacitance, the STM8T141 device employs bursts of

charge transfer cycles. Consequently, charges accumulated into the electrode capacitance

are transferred to a sampling capacitor. This operation is repeated N times until the voltage

on the sampling capacitor reaches a given threshold. The number, N, of transfer cycles

required to reach the threshold represents the size of the electrode capacitance. N varies

when the electrode is touched.

2.2

What are the targeted applications?

The STM8T141 opens up a range of new opportunities and a wide number of application

domains still need to be explored.

The power supply (2 V to 5.5 V) of the product and its extremely compact package size

(either UFDFPN8 2 x 3 mm or SO8 narrow) benefits battery powered systems for integration

in miniature environments.

The device is suitable for the following functions:

●

On/off switch or activation button.

●

Wake-up function on user touch for power critical equipment and long battery lifetime.

●

Backlight control on proximity detection.

Below, are listed several application examples:

●

Elimination of mechanical buttons or on/off switches in high volume applications such

as DVD/CD drives, computers, and coffee machines to enhance system reliability.

●

Home button in GPS systems for easy and safe navigation in the application menu.

●

Light activation switches on user touch and backlight on user proximity of wall switch

outlets.

●

A simple button to control power, audio line or volume adjustment in Bluetooth

headsets.

●

User ear or head detection in MP3 headphones to automatically play/stop music. The

electrode is placed in the earpiece for nearby detection.

●

Cost-effective solutions to replace Infrared proximity sensors in mobile phones for ear-

face detection.

●

User approach detection to wake-up wireless mice or keyboards.

●

LCD TV front panel backlight control on hand detection.