Sensors & transducers
How a temperature, a pressure or a heartbeat becomes a number: the transducer that converts physiology to a voltage, then the chain that digitises it.
In one line
A transducer converts one form of energy into another; a sensor turns a physical quantity — temperature, pressure, light, motion, bio-potential — into an electrical signal. Everything measured in digital health starts here.
<figure style="text-align:center;margin:1.5rem 0"> <svg viewBox="0 0 440 120" role="img" aria-label="Signal chain: physiology to transducer to amplify and filter to ADC to a number" style="width:100%;max-width:460px;height:auto;color:var(--c-iot)"> <text x="40" y="55" font-size="11" fill="var(--text-3)" text-anchor="middle">physiology</text> <text x="40" y="70" font-size="10" fill="var(--text-3)" text-anchor="middle">(heat, pressure)</text> <line x1="78" y1="55" x2="108" y2="55" stroke="currentColor" stroke-width="2"/><polygon points="100,50 110,55 100,60" fill="currentColor"/> <rect x="110" y="35" width="80" height="40" rx="6" fill="none" stroke="currentColor" stroke-width="2"/><text x="150" y="59" font-size="11" fill="currentColor" text-anchor="middle">transducer</text> <line x1="190" y1="55" x2="220" y2="55" stroke="currentColor" stroke-width="2"/><polygon points="212,50 222,55 212,60" fill="currentColor"/> <rect x="222" y="35" width="92" height="40" rx="6" fill="none" stroke="currentColor" stroke-width="2"/><text x="268" y="52" font-size="10.5" fill="currentColor" text-anchor="middle">amplify</text><text x="268" y="66" font-size="10.5" fill="currentColor" text-anchor="middle">+ filter</text> <line x1="314" y1="55" x2="344" y2="55" stroke="currentColor" stroke-width="2"/><polygon points="336,50 346,55 336,60" fill="currentColor"/> <rect x="346" y="35" width="56" height="40" rx="6" fill="none" stroke="currentColor" stroke-width="2"/><text x="374" y="59" font-size="11" fill="currentColor" text-anchor="middle">ADC</text> <text x="374" y="92" font-size="10.5" fill="var(--text-3)" text-anchor="middle">to a number</text> </svg> </figure>How it works
A raw sensor signal is tiny and noisy, so a signal chain conditions it:
- Transduce — the element changes an electrical property with the quantity (a thermistor's resistance with temperature; an electrode's voltage with heart activity).
- Amplify & filter — an op-amp front-end boosts and de-noises.
- Digitise — an ADC samples it into numbers.
Sensors you'll meet in health
| Quantity | Transducer | Device |
|---|---|---|
| Temperature | thermistor / IR | thermometer, incubator |
| Blood oxygen | LED + photodiode | pulse oximeter |
| Pressure | strain gauge / MEMS | BP cuff, ventilator |
| Heart electrical | electrode | ECG |
| Motion / falls | MEMS accelerometer | wearable |
| Glucose | electrochemical | glucometer, CGM |
Where it goes next
The numbers an MCU collects become FHIR Observations with LOINC codes and UCUM units — the data the interoperability labs work with. The hardware is where data is born.
Watch for
Two numbers decide trust: accuracy (closeness to truth) and precision (repeatability). A dashboard built on a poorly-conditioned sensor is still wrong.