Meet LESENSE: Your Sensors’ Low-Power Hardware Watchdog

Think of an embedded system like a busy data center. You’ve got a powerful CPU at the core, but it’s expensive to keep it running all the time. Instead, you offload repetitive, lightweight tasks to specialized controllers that consume less energy.

That’s exactly what Silicon Labs’ LESENSE (Low Energy Sensor Interface) is:

A low-power coprocessor for sensors that keeps monitoring signals while letting the main CPU sleep. It continuously monitors external signals, filters noise, and applies decision logic while the main CPU remains in sleep mode. Only when meaningful data is detected does it take action. This makes it possible for developers to build IoT systems for long term use without draining batteries.

What is LESENSE?

LESENSE is a dedicated subsystem inside certain Silicon Labs MCUs that functions as a complete sensing engine. It can generate excitation signals using GPIOs or the on-chip DAC, measure responses through comparators or ADCs, apply logical evaluations with a built-in state machine, and route events autonomously through the Peripheral Reflex System (PRS), Direct Memory Access (DMA), or interrupts.

In other words, LESENSE acts like a signal acquisition engine + decision unit. It operates even in deep sleep energy modes such as EM2, leaving the CPU completely idle until needed. By keeping sensing activity in hardware, the system saves significant energy while still behaving as if it were always on.

Why LESENSE is Like a Hardware Watchdog for Sensors

In hardware terms, LESENSE works like a watchdog timer, but instead of checking CPU activity, it’s checking sensor activity. In this case, the watchdog loop is the programmable state machine. Trigger conditions come from thresholds or patterns you configure.

Certain sensor conditions, state transitions, or even other peripherals connected through the PRS can trigger a CPU wake-up. In practice, this creates a watchdog-style safety net for your sensor network. The system never misses an event, yet it consumes only a trickle of power while waiting.

This gives your system constant vigilance with almost zero energy costs.

LESENSE Key Features

• Sensor Multiplexing → Like a 16-channel ADC front-end, LESENSE can manage multiple inputs.
• State Machine = Finite Automaton → Engineers can think of it as a small FSM engine embedded in hardware, running predefined sensing states.
• Energy-Friendly Signal Chain → Excitation → Capture → Compare → Filter → Action, all performed without CPU involvement.
• DMA Integration → Acts like a data mover, pushing results into memory without software overhead.
• Noise Rejection → Built-in hysteresis and filters act like hardware debouncing for sensors.

Practical Applications of Our Low Energy Sensor Interface

The low-power vigilance of LESENSE lends itself to a wide range of real-world applications. In smart meters, for example, LESENSE is often used as a tamper-detection coprocessor. It continuously excites inductive coils and monitors for anomalies that indicate magnetic interference. This happens around the clock without draining the meter’s energy reserves.

In industrial systems, LESENSE can function as a proximity detector module, monitoring for metal objects and logging detection events without needing the CPU to poll sensors. Smart agriculture offers another compelling case, where LESENSE works like a low-power ADC scheduler, periodically polling soil moisture sensors. The CPU only wakes if readings cross predefined thresholds, ensuring that power is spent only when action is required.

Wearables and medical devices also benefit. Here LESENSE can monitor biosignals such as changes in resistance or chemical activity, performing background checks while the rest of the system conserves energy. This approach extends battery life and allows developers to meet stringent power budgets in compact devices.

LESENSE in Action: Inductive Tamper Detection

Let’s frame it like a signal chain block diagram:

• Excite - DAC drives the LC sensor coil.
• Sense - Comparator checks the coils response.
• Evaluate - LESENSE state machine compares against thresholds.
• Decide - PRS routes event → interrupt/DMA → CPU wake if needed.

This flow is identical to having a dedicated low-power monitoring circuit that integrates seamlessly into the MCU fabric.

Why Developers Should Treat LESENSE Like a Coprocessor

LESENSE isn’t just another MCU peripheral. A more accurate way to think about it is as a true coprocessor. It delivers significant power efficiency by allowing the main processor to stay asleep while important background checks continue. It reduces firmware complexity because repetitive signal monitoring tasks no longer require software loops. It scales easily to different sensor technologies, providing a flexible base that can adapt to multiple designs without overhauling the system.

Perhaps most importantly, LESENSE builds robustness into the system at the hardware level. With noise filtering and debouncing embedded in silicon, false interrupts are minimized, and firmware can focus on meaningful data rather than chasing noise.

LESENSE is not simply a peripheral on Silicon Labs MCUs. It is a purpose-built coprocessor for sensors, enabling embedded systems to maintain continuous awareness of the physical world while consuming very little energy. It allows devices to stay in deep sleep most of the time and wake only when events of interest occur.

LESENSE is Your Sensors’ Hardware Watchdog

For engineers, this means longer battery life, simplified firmware design, and more reliable sensing across diverse applications. If you are building IoT devices that require always-on monitoring but must respect strict energy budgets, LESENSE deserves a place in your design toolbox. If you’re designing an IoT device where always-on monitoring meets tight energy budgets, LESENSE should be part of your toolbox - the hardware watchdog that never sleeps.