Touch or proximity detection solution based on STM8T141

STM8T141 is a single fully integrated charge transfer capacitive sensor with built-in drive and shield functions for touch or proximity detection, replacing traditional mechanical switches in cost-sensitive applications . It is mainly used in consumer electronics , home and office equipment, battery and critical power applications, etc. This article introduces the main features of STM8T141, block diagram, measurement circuit diagram, typical application circuit diagram, surface capacitance sensor equivalent capacitance circuit, portable application equivalent circuit diagram and STM8T14X-EVAL evaluation board main features, evaluation board and module (MB858) circuit diagram .

STM8T141: Single-channel capacitive sensor for touch or proximity detection with shielded sensing electrode

The STM8T141 is a ProxSense™ single-channel, fully integrated, charge-transfer, capacitive sensor that is designed to replace conventional electromechanical switches in cost-sensitive applications.

The STM8T141 is offered in 8-pin packages and is ideally suited for 1-button applications. It can be configured either in touch or proximity sensing mode for wake-up or backlighting on actuation. The extremely low current consumption makes it an ideal solution for battery-powered applications.

The device features an internal voltage regulator to enhance detection sensitivity and stability. The STM8T141 touchpad can sense through almost any dielectric and can thereby contain the electronics in a sea led environment.

The STM8T141 also incorporates the advantages of using a driven shielding capability. This makes it possible to separate the sealed electronics from the sensing electrode. The shield feature enables the designer to protect part of the sensing element from unwanted environmental interference and enhances proximity detection when used with battery (DC) applications.

STM8T141 main features:

■ Touch or proximity detection (a few centimeters)

■ Built-in driven shield function:

– Enhance proximity detection

– Protect sensing electrode from noise interference

■ Ultra-low power modes suitable for battery applications (11 μA in extreme low power mode)

■ On-chip integrated voltage regulator

■ Environment compensation filter

■ User programmable options include:

– Four detection thresholds

– Four output modes

– Four low power modes

– Reference freeze timeout

■ Minimal external components

STM8T141 Applications:

■ Consumer electronics

■ Power-critical and battery applications

– Wake-up on proximity

■ Home and office appliances

– Find-in-the-dark (FITD) applications using proximity detection

– Sanitary ware and white goods

■ Flameproof human interface devices for use in hazardous environments

Figure 1. STM8T141 block diagram

Figure 2. STM8T141 measurement circuit diagram

Figure 3. Typical application circuit diagram of STM8T141

Figure 4. Equivalent capacitance circuit of surface capacitance sensor

Figure 5. Equivalent circuit diagram for handheld applications

STM8T14X-EVAL evaluation board

The STM8T14X-EVAL is an evaluation kit which introduces developers to STMicroelectronics STM8T141 touch and proximity capacitive sensor. It contains an STM8T141 evaluation board, the MB858, plus a set of preconfigured plug-in modules which allow to evaluate STM8T141 device performances in either touch or proximity detection (depending on the module which has been plugged in).

STM8T14X-EVAL evaluation board main features:

The evaluation kit features are the following:

■ Touch detection with on-board PCB sensing electrode and 1.5 mm dielectric panel

■ Easy dielectric adjustment by stacking acrylic panels

■ Proximity detection with on-board PCB sensing electrode or plug-in antenna

■ Standalone power configuration using an on-board battery

■ External power supply through USB interface

■ Electrode grounding or shielding configured by jumper

The STM8T14X-EVAL kit includes:

● 1 STM8T141 evaluation board (MB858)

● 4 STM8T141 preconfigured plug-in modules (MB856)

● 1 antenna shielding cable

● 1 additional 3 mm acrylic panel

Figure 6. STM8T14X-EVAL evaluation board outline

Figure 7. MB858 evaluation board and plugged-in STM8T141 module

Figure 8. Circuit diagram of STM8T141 evaluation board (MB858)

Figure 9. STM8T141 module (MB858) circuit diagram