Sensor selection fails in a predictable way: an engineer picks a part by its headline accuracy, ships the product, and discovers drift, power budget overruns, or an interface that eats the whole firmware schedule. This guide walks the main sensor families and the five specifications that actually determine fit.
The Main Families, and What They Are Good At
| Family | What It Measures | Typical Output | Watch Out For |
|---|---|---|---|
| Temperature | Ambient / object / die temperature | Analog (mV/°C), I2C/SMBus digital | Self-heating from excitation current; PCB heat paths dominate system accuracy |
| Pressure | Absolute / gauge / differential | Bridge (analog), digital I2C/SPI | Media compatibility, temperature compensation, overpressure rating |
| Motion / IMU | Acceleration, rotation | SPI/I2C digital | Offset drift, scale-factor tolerance, alignment of axes to the product |
| Proximity / ToF | Presence, distance | Digital I2C, GPIO | Target reflectivity, ambient light rejection, cover-glass crosstalk |
| Optical / ambient light | Illuminance, color | I2C digital | Spectral response vs. human eye, IR contamination, flicker (50/60 Hz) |
Five Specifications That Decide Fit
- Accuracy over conditions, not at 25 °C. The headline number is usually the room-temperature best case. Read the accuracy-over-temperature table — a "±0.1 °C" sensor that degrades to ±0.8 °C across your range changes the whole design.
- Resolution vs. noise. A 20-bit ADC behind a noisy element is marketing, not precision. Ask for effective resolution at your bandwidth.
- Long-term drift and repeatability. For anything measuring over months — pressure, humidity, gas — drift dominates. Check the specification and the calibration story.
- Power profile. Battery products live on the average, not the peak: a sensor drawing 2 µA at 1 Hz sampling beats one drawing 300 µA continuously with better headline accuracy.
- Interface and integration cost. Digital (I2C/SPI) parts bundle calibration and compensation; analog parts are cheaper and simpler but move every error budget concern into your layout and firmware.
Interfacing Without Surprises
- I2C sensors: confirm the address map across your whole bus, check bus capacitance and pull-up sizing, and implement the clock-stretching quirk some devices have.
- SPI sensors: verify mode (CPOL/CPHA), maximum clock at the supply voltage you actually use, and word framing for 24-bit conversions.
- Analog bridges and ratiometric outputs: excite the bridge from the same reference as the ADC so ratiometric errors cancel; keep excitation lines Kelvin-sensed.
- Grounding: keep sensor returns star-routed; a few millivolts of ground bounce is a large error on a 100 mV full-scale signal.
A Selection Workflow That Ends Well
Define the measurement (range, accuracy in system, bandwidth, environment), then the interface and power budget, and only then open the distributor catalog. Shortlist by the datasheet's conditions tables, buy samples with different date codes, and validate drift on real hardware before committing the layout. JTDZ Tech carries temperature, pressure, motion, proximity, and optical sensors from major manufacturers — tell us what you are measuring and we will shortlist parts with datasheets, date codes, and alternates.
