Resistors

In one line

A resistor pushes back on current. How hard, in ohms, is set by Ohm's law: V = I × R.

<figure style="text-align:center;margin:1.5rem 0"> <svg viewBox="0 0 280 90" role="img" aria-label="Resistor symbol: a zig-zag between two wires" style="width:100%;max-width:320px;height:auto;color:var(--c-iot)"> <line x1="14" y1="45" x2="80" y2="45" stroke="currentColor" stroke-width="2"/> <polyline points="80,45 90,25 110,65 130,25 150,65 170,25 190,65 200,45" fill="none" stroke="currentColor" stroke-width="2.5"/> <line x1="200" y1="45" x2="266" y2="45" stroke="currentColor" stroke-width="2"/> <text x="140" y="84" font-size="11" fill="var(--text-3)" text-anchor="middle">resistance R (ohms) — opposes current flow</text> </svg> </figure>

How it works

• Limit current so a downstream part isn't destroyed — e.g. the resistor in series with an LED.
• Divide voltage — two resistors in series split a voltage (a voltage divider). This turns a variable resistance — a temperature- or pressure-sensitive element — into a voltage a chip can read.

Where it shows up in digital health

• A thermistor in a thermometer or incubator sits in a voltage divider; the chip reads it and converts to °C.
• Pull-up / pull-down resistors hold a digital line at a known state.
• Current-sense resistors measure motor/pump current — a way to detect an occlusion electrically.

Watch for

Resistors have a tolerance (±1%, ±5%) and a power rating. In a measurement front-end, tolerance directly limits how accurate the reading can be.