Distance Sensor
A distance sensor turns a measurement of a target into a usable output. Some report a numerical range, some provide an analog signal, and others only indicate whether a target crosses a set distance. The measurement principle and output type must be checked separately.
Optical time-of-flight uses the travel behavior of emitted and reflected light. Direct ToF measures return timing; indirect ToF can measure the phase of modulated light. Triangulation instead uses the position of a reflected light spot on a detector. A sensor's output may need conversion or interpretation rather than being a voltage directly proportional to distance.
In plain terms
There is more than one way to find a wall: time an echo, or look at it from a known angle. Distance sensors use different physical clues, so they do not all share the same wiring, output or blind spots.
Why designers use it
- Provide range information for a suitable robot or user interface.
- Detect a target entering a chosen distance region.
- Obtain depth or movement information with a sensor designed for that measurement.
Best for
- Range measurement
- Object detection
- Depth and gesture experiments
Key specifications
- Measurement method: Check the selected device (Different principles respond differently to the target and environment.)
- Output: Range value, analog signal or threshold (Confirm the interface and the meaning of the output.)
- Range and uncertainty: Use the stated test conditions (Resolution is not the same as accuracy.)
When not to use it
- When the target, ambient light, field of view, cover or timing settings lie outside the sensor's validated conditions.
- When the application needs a numerical distance but the selected device provides only a threshold output.
Common mistakes
- Assuming all distance sensors time an echo.
- Treating an analog output as a linear distance scale without checking its transfer characteristic.
- Ignoring minimum range, field of view and the device's behavior when no valid target is found.
- Changing a laser-based sensor's optics without checking the manufacturer's measurement and eye-safety requirements.
Where you will find it
- Sharp's application note contrasts GP2Y0A analog-output sensors with GP2Y0D one-bit threshold-output sensors. Both use optical triangulation, but their outputs serve different tasks.
- ST's FlightSense presentation describes direct-ToF modules and shows that long-range results depend on target reflectance, timing budget, optics and ambient infrared light.
A short history
Distance sensing is a measurement task rather than a single circuit architecture. Sharp's note explains spot-position triangulation; TI explains time-of-flight depth measurement; ST presents compact direct-ToF modules. Comparing these sources helps separate the physical principle from the interface and the performance conditions.
Good to know
- A one-bit output can answer whether a target has crossed a threshold without reporting its exact distance.
- A displayed millimetre unit does not, by itself, establish millimetre accuracy.