FMCW Radar: How a $50 Chip Reads Your Heartbeat Through a Wall
The Texas Instruments IWR6843 is a 77 GHz FMCW radar evaluation board used in automotive collision avoidance. It also extracts heart rate, respiratory rate, and HRV from a person through a wall at six metres. Here is how.
Published 2025-02-28
The radar sensor in your car's blind spot monitor uses FMCW — Frequency Modulated Continuous Wave — radar. It sweeps a chirp signal across a frequency range, mixes the transmitted and received versions, and extracts range and velocity from the resulting beat frequency. The same physics that detects a car at 30 metres detects the 5 mm chest wall displacement of a breathing human at 6 metres. The same chip. The same firmware. A different signal processing pipeline at the end. The Texas Instruments IWR6843 evaluation board costs approximately $50. The Physics Ranging FMCW transmits a chirp — a signal that sweeps linearly from frequency f₁ to f₂ over a period T . When this reflects off a target at range R , it returns delayed by τ = 2R/c (speed of light). Mixing the transmitted and received signals produces a beat frequency: Where BW is the sweep bandwidth. For the IWR6843 at 77 GHz with 4 GHz bandwidth, range resolution is approximately 3.75 cm — enough to distinguish your chest from a wall behind you. Velocity (Doppler) If the target is moving, successive chirps observe a phase shift proportional to velocity. The 5 mm displacement of a breathing chest produces a Doppler phase shift detectable at 77 GHz even at 6 metres range. Heartbeat produces smaller displacement — approximately 0.5 mm — but at 77 GHz, even sub millimetre motion generates measurable phase change. Heart rate can be extracted to ±1 bpm accuracy from 30 frames of data (1.5 seconds at 20 Hz update rate). Range Doppler Processing: Separating the Target from the Room A restaurant has 70 people. How does the…
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