Perpetual Wearable Biosensing with Andy Kong

Chris welcomes Andy Kong to discuss “ Chargerless ” and how to build ultra-low-power wearable health trackers that never need wall charging. (00:00:15) From Hacker Mindset to Startup Founder : They discuss Andy’s background in biosensing, staying with Samy Kamkar , and bringing a pragmatic “get things done” hacker mindset to founding Chargerless in San Francisco, as documented on Andy’s personal website . (00:02:10) Solving the Wearable Charging Bottleneck : Andy explains how frustration with daily Apple Watch charging led him to design a wearable requiring only one minute of daily sunlight exposure, noting that modern wearables are bottlenecked by battery volume rather than logic chip size. (00:04:30) Deliberately Underpowered MCUs : Chris and Andy explore system architecture trade-offs, focusing on Chargerless’s choice of an underpowered microcontroller paired with lean firmware rather than feature-heavy, power-hungry processors. (00:07:15) Intelligent Sampling vs. Continuous Monitoring : They contrast Whoop and Apple Watch’s continuous PPG power drain with Chargerless’s periodic sampling approach, which reserves high-frequency tracking for active workout modes. (00:09:45) The Limits of Commercial Sensor ICs : Why off-the-shelf health ICs from TI and Analog Devices consumed 100 times too much power due to unoptimized ADCs, inefficient amplifiers, and fixed pulse timings. (00:12:20) EKG vs. Wrist PPG : Explaining how multi-lead chest EKGs measure electrical heart potential vectors, whereas wrist Photoplethysmography (PPG) uses green light reflection to detect oxygenated blood volume changes. (00:15:05) Badge Life and DIY Biometrics : Chris and Andy reminisce about community hardware projects like Chaos Camp’s Card10 EKG badge , Kerry Scharfglass’s IR-synchronized dragonfly badge , and Chris’s earlobe PPG sensor that flashed LEDs inside a Solo cup based “badge”. (00:17:50) Custom Discrete PPG Frontend : How Andy replaced commercial ICs with a discrete circuit that strobes a green LED 50 times per second for microsecond bursts, cycling both the LED and transimpedance amplifier. (00:20:40) Eliminating Decoupling Lag : Stripping decoupling capacitors removed turn-on delays, while using two amplifier stages avoided high-capacitance digital potentiometers. (00:23:10) Pivoting Away from BCI : Andy describes his college research on brain-computer interfaces (BCIs) with OpenBCI and why he abandoned non-invasive EEG due to microvolt-level signal noise from cable movement. (00:25:55) Quantified Self & Personal Informatics : Discussing how self-trackers capture environmental data to identify root causes of complex health symptoms. (00:28:30) Low-Power Bluetooth Data Batching : How Bluetooth Low Energy accounts for less than 5% of overall power draw by batching 10 KB payloads every 10 minutes for fast burst transmissions to the phone. (00:31:15) Form Factors and Ring Safety : Comparing Whoop, Oura, Garmin, and Fitbit Air trackers, while covering smart ring battery constraints, Samsung battery recall testing, and degloving risks. (00:34:00) Whoop’s Slide-On Battery : How Whoop designed a slide-on battery pack to charge while being worn, avoiding the user drop-off caused when devices are taken off to charge. (00:36:45) Solar Harvesting & Laser Dicing : Chargerless uses boost converters to harvest power from amorphous