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Shun Matsuo
Shun Matsuo
IoT Product Engineer

In recent years, demand for low power consumption in HMI (Human Machine Interface) applications using capacitive touch sensors has been growing at the same pace as battery-powered devices and eco-friendly products.

To address these demands, Renesas offers the smart wakeup solution using the latest RX140 MCU snooze mode and the CTSU2SL’s (Capacitive Touch Sensing Unit) new features to realize a significant reduction of standby power consumption. This solution uses Capacitive Touch Evaluation System for RX140 and Touchless Button Demo, as described in the application note published on our website.

This sample software uses new functions of the CTSU2SL, Multiple Electrode Connection (MEC), and Automatic Judgement to detect activation of the touch button during snooze mode and switch to the normal operation mode. Since the MEC function allows multiple touch buttons to be measured as one, multiple measurements are not required and touch can be detected in a shorter time duration. The shorter measurement time results in less power consumption. 

In addition, the Automatic Judgement function makes the process of touch detection by the CPU unnecessary. When a touch is detected in snooze mode, it switches to the normal operation mode. When a touch is not detected, it returns to software standby mode and keeps power consumption to a minimum.

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Diagrams

Aside from low power consumption, the MEC function has the extra advantage of extended detection distance of touchless buttons from conventional 15mm up to about 60mm. In principle, the change in capacitance is disproportional to the distance between a finger and an electrode and proportional to the contact area. Since the MEC function handles multiple touch buttons as a single large one, the detection distance can be achieved up to 60mm when hovering a palm over the demo machine.

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Detection distance

The smart wakeup solution offers the low-power consumption of capacitive touch sensing. The RX140 can make it easier to install capacitive touch sensors not only in battery-powered devices, such as in electronic keys and small home appliances, but also in other applications that have strict requirements on power consumption. For such cases, we highly recommend the well-suited RX140!

Note: The CTSU2SL is incorporated in the RX140 MCU with 128KB flash memory or more. The MCU with 64KB flash memory incorporates CTSU2L, which does not support Automatic Judgement and the MEC functions.

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