Design Methodology · Study deck

Sensor Selection: Requirements and Candidate Screening

A sensor shortlist starts with a range, the lowest and highest values it must measure.

Blueprint Bina is your guide for this deck.

specsheetsensor

Blueprint Bina, the module guide, in a scene from this chapter.

After studying this chapter

Learning objectives

You will be able to:

Test requirements before parts with a concrete scenario and pass criteria.
Validate references with a concrete scenario and pass criteria.
Explain: The brief can be short, but it must be specific enough to reject a candidate.
Explain: A gate has a pass, fail, or investigate result.

Major section

Requirements Before Parts

The brief can be short, but it must be specific enough to reject a candidate.

The interface check separates analog and digital options before the decision summary combines range, accuracy, and connection needs.
Current by mode, conversion time, startup time, duty-cycle assumptions, and regulator limits.
I2C, SPI, UART, analog, address options, timing, pullups, logic levels, and driver support.

A sensor shortlist should start from the measured quantity and interface constraints before comparing individual part numbers.

Major section

Mandatory Gates First

A gate has a pass, fail, or investigate result.

Host logic exceeds sensor I/O limit.
Sensor saturates before the required event is captured.
Worst-case error is within the required limit under relevant conditions.
Average and peak current fit regulator, battery, thermal, and firmware assumptions.

Major section

Incremental Examples

A classroom comfort sensor needs temperature and humidity updates every few minutes, not pressure or high-rate motion.

A BME280 can be a viable candidate if the product also needs barometric pressure; a Sensirion SHT31-DIS-style humidity sensor may be a better-focused candidate when pressure is irrelevant.
The first gate is not brand preference.
A wearable fall-detection prototype might compare LIS3DH and ADXL345-style accelerometers.

Major section

Weighted Scoring Is a Trade-off Tool

Weighted scoring is useful when the remaining candidates all meet the gates.

It should not pretend to be more precise than the evidence supports.
Weighted scoring only helps after hard sensor requirements are met.
The final sensitivity step asks whether plausible weights change the leader.

Weighted scoring belongs after mandatory gates and before bench validation, not before basic fit is proven.

Major section

Power Review Without False Precision

For battery systems, record every state that the firmware can enter.

Average current is only meaningful when the duty cycle is realistic.
Short bursts can exceed regulator or battery pulse limits.
Measured current after final board leakage and pullups are included.
Board leakage can dominate the sensor datasheet value.

Major section

Interface and Firmware Checks

The selected sensor must match both hardware and firmware, not just the block diagram.

Schematic review and absolute maximum pin limits.
Bus speed, setup, hold, conversion, and interrupt timing.
Driver reads before data is valid.
Firmware assumes a default mode that the part does not use.

Major section

Application Snapshots

The best sensor depends on the project requirements and final evidence.

Wearable motion Accelerometer or IMU Gate on range, output data rate, current states, package, interface, interrupt behavior, and mounting orientation.
Environmental node Pressure, humidity, temperature Gate on operating range, accuracy over temperature, recovery from condensation, enclosure airflow, supply, current, and calibration needs.
A scorecard cannot replace safety analysis.

Deck summary

Key takeaways

The brief can be short, but it must be specific enough to reject a candidate.

A gate has a pass, fail, or investigate result.
A classroom comfort sensor needs temperature and humidity updates every few minutes, not pressure or high-rate motion.
Weighted scoring is useful when the remaining candidates all meet the gates.
For battery systems, record every state that the firmware can enter.

Retrieval practice

Recall check 1 of 3

Blueprint Bina says: answer from memory, then check your reasoning.

Q1What names the measurand, range, accuracy, timing and environment before comparing sensors?

AMandatory Gates

BDatasheet Evidence

CSensing Claim

DTrade-off Scoring

Show answer

Answer: C The sensing claim names the measurand, operating range, accuracy, timing, and environment before parts are compared.

Retrieval practice

Recall check 2 of 3

Blueprint Bina says: answer from memory, then check your reasoning.

Q2A candidate sensor has the highest weighted score, but its recommended operating temperature range does not cover the deployment environment. What should the review do?

AKeep it because a high weighted score can outweigh one formal operating-temperature requirement miss.

BAverage the temperature score with power and cost to hide the issue.

CReject it unless the requirement or deployment environment is formally changed and verified.

DUse the absolute maximum temperature rating as the normal operating range.

Show answer

Answer: C Mandatory requirements must pass before scoring begins.

Retrieval practice

Recall check 3 of 3

Blueprint Bina says: answer from memory, then check your reasoning.

Q3A low-power sensor datasheet lists active current, sleep current, and startup time. What should the power review include before accepting a battery-life claim?

AUse nominal battery and sleep current, omitting startup and leakage.

BUse active current alone because it is the largest listed draw.

CAccept the claim from the low-power mode name without board data.

DModel duty cycle; measure board startup, interface, sleep, active, and leakage.

Show answer

Answer: D A defensible power claim combines datasheet rows, firmware state timing, measured board current, and battery assumptions.

Print reference

Answers

Answer key.

C · The sensing claim names the measurand, operating range, accuracy, timing, and environment before parts are compared.
C · Mandatory requirements must pass before scoring begins.
D · A defensible power claim combines datasheet rows, firmware state timing, measured board current, and battery assumptions.