2026

[040] NFC TEMPERATURE LOGGER

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The starting constraint was easy to state and hard to meet: a standalone temperature logger, smaller than a one-euro coin, with the longest possible battery life, and contactless data retrieval.

The form factor forces brutal decisions from the start. No room for a large cell, no room for a conventional radio module, no room to afford ordinary standby consumption. Every microamp has to be justified.

The STM32L031G6U3TR was the obvious pick. It’s one of the most compact STM32 microcontrollers available — UFQ package, 3×3 mm — and it comes with the low-power modes needed to survive in very tight energy budgets. In stop mode with the RTC running, consumption drops to a few hundred nanoamps. On a small cell, that translates to months of autonomous operation.

Temperature measurement is handled by an external sensor selected for its footprint and current draw. The micro wakes up on a timer, takes a measurement, timestamps it, writes it to storage, and goes back to sleep. As simple as possible on the logic side, as frugal as possible on the energy side.

For data retrieval: NFC Mailbox. No permanent radio, no Bluetooth, no antenna burning current in standby. Bring a smartphone close, the NFC field partially powers the circuit, and the logged data is read directly from memory. Clean, instant, no dedicated battery needed on the reader side.

This project is a good example of what “design under constraint” actually means in practice: every single decision is a negotiation between size, power, and functionality.

[039] CUSTOM CAPACITIVE TOUCHPAD

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Designing a touchpad feels like a standard project — until you start pinning down the actual constraints. Here, the sensing surface was long. Very long. And the geometry ruled out any off-the-shelf electrode layout.

The chosen electrode pattern is diamond-shaped. That’s not an arbitrary call: this geometry optimizes surface coverage while minimizing dead zones between detection nodes. On a large touchpad, it makes a real difference in terms of position linearity and detection consistency across the full length.

The problem is that the physical length of the circuit exceeded what a single capacitive touch controller could handle. The solution: two IQS9150 devices cascaded together. The IQS9150 is an Azoteq controller designed for capacitive matrix management — it handles electrode excitation, capacitance measurement, and position computation internally. Chaining two of them required careful synchronization and data sharing to make both halves of the touchpad behave as a single, coherent surface.

The electrode design itself went through several iterations. Each diamond cell has to be sized for adequate sensitivity without creating parasitic coupling between adjacent electrodes. PCB routing also needs to minimize stray capacitance to the ground plane, which directly degrades measurement dynamic range.