Tagged medical
7 pieces
- · 9 min read
You Cannot Hire a Gap: Why Cross-Layer Failures Have No Owner
The analog engineer designed a correct reference loop. The actuation engineer designed a correct current source with a safety limit. The mechanical engineer placed the electrodes correctly. Every one of them did excellent work inside their lane, and the device failed, because the failure lived in the loop connecting all three and that loop was on nobody's schematic. A seam is not a gap in anyone's competence. It is the region between all of your competent people.
- · 7 min read
The Physical Ceiling: What No Model Can Recover From Your Sensor
Whatever your sensor and that first little circuit throw away is gone. You cannot get it back later with software. A photo that comes out blurry does not become sharp with editing, and the fancy tools that appear to sharpen it are inventing plausible detail rather than recovering real detail, which is exactly the distinction that matters when the output drives a decision about a person.
- · 8 min read
The Driven Reference Electrode: Your Front End's Hero and Its Hidden Risk
The third electrode is a feedback loop wrapped around a person. It senses the body's common mode and drives against it, which is what turns a hope about electrode symmetry into an actively regulated quantity and gives you rejection figures worth quoting. It is also a deliberately low-impedance connection between your circuit and the body, which makes it a stability problem, a safety-limited path, and the exact node any injected current will come home through.
- · 7 min read
Common Mode Rejection: How a Biosignal Front End Hears a Whisper at a Concert
When you measure off a body you are not measuring your signal. You are measuring your signal plus the person plus the room, all summed at the amplifier, and the thing you want is microvolts while the mains hum coupling into the person can be a thousand times larger. The entire job of the front end is pulling the small thing out from under the large thing, by throwing away everything that appears equally on both inputs.
- · 7 min read
Your Bill of Materials Passes and Your Board Is Still Wrong: Topology vs Parts
Two current-limit resistors in series for redundancy is good design. The same two resistors, both the correct value, placed in parallel instead, quarters your limiting and roughly doubles the current. Every part inspection passes, because both resistors are the right value and the bill of materials is correct. The failure is not in the parts, it is in the topology, and your incoming checks do not look at topology.
- · 18 min read
Sensor Placement Is an Algorithm Decision
On a wearable device, where the sensor physically sits is not a comfort decision, it is the decision that determines whether you need an AI model at all, and whether you ship in 6 months or 18. It is usually made in month 2 by someone who does not work on signals, and by month 9 it has quietly become a year-long AI project nobody planned.
- · 16 min read
The Return-Path Bug That Kills Your Biosignal Front End
On a closed-loop bio device, the instant you turn the actuator on, the signal can vanish to a flat line, and it is not coupling. The current you inject is a loop that has to come home, and it takes the lowest-impedance path, often the exact electrode protecting your front end. It forces a voltage the amplifier cannot reach, the amplifier rails, and your sensor goes blind. The fix is a decision about where the current returns, not a better part.