Laser rangefinder module evaluation checklist (design-in)
Maintained by ERDI TECH LTD (ERDILRF). This checklist is vendor-neutral in form but ERDI-specific in the links; it exists because most integration failures we see are caused by comparing headline range numbers instead of comparing measurement conditions.
Use it before you request samples, and again before you freeze a mechanical design.
1. Define the measurement, not the number
Write down, in one line each:
- target material and approximate reflectivity at the laser wavelength;
- target size at the closest and farthest working distance;
- expected ambient light (indoor, overcast, direct sun);
- required update rate and whether the platform moves during a measurement;
- required accuracy and the acceptable outlier rate;
- mounting envelope, window material, and cable route.
A module that reaches 200 m on a cooperative target may reach a small fraction of that on a low-reflectivity target in bright light. ERDI publishes the conditions next to the numbers on each model page, for example LRF200H distinguishes 90% and 10% reflectivity cases. Read those conditions as part of the specification.
2. Interface and electrical
| Check | Why it matters |
|---|---|
| UART logic level (3.3 V or 5 V TTL) | The supply voltage does not tell you the signal voltage. Confirm both. |
| Supply voltage range and peak current | A module that browns out during a measurement returns plausible-looking bad data. |
| Connector pinout and mating part | Pin order is not standard across vendors. |
| Cable length and shielding | Long unshielded UART runs pick up motor and ESC noise. |
| Start-up time and first valid frame | Some hosts log the boot frame as a measurement. |
Background: UART/TTL integration guide.
3. Protocol and data quality
- Ask for the frame description, not only a driver binary.
- Confirm checksum coverage and what the device does on a bad frame.
- Confirm the unit of the distance field (metres, centimetres, millimetres) and whether it is signed.
- Confirm the status/confidence field and its meaning.
- Log raw frames for the first bench session; parsing bugs look like sensor noise.
Protocol notes for the two ERDI families are in Protocol A and Protocol B; the general checksum pattern is described in frame and checksum basics.
4. Optical and mechanical
- Spot size grows with distance: diameter is roughly
2 * range * tan(divergence/2). At long range the spot can be larger than the target. - Window tilt and coating cause internal reflections that appear as a short false range.
- Confirm the reference plane: front face, mounting face, or connector face.
- Check whether the module expects a bandpass window; a plain acrylic window may pass ambient light but block or distort the return.
See beam divergence and spot size and update rate on moving platforms.
5. Environmental and safety
- Operating and storage temperature, and whether accuracy is specified across it.
- Ingress protection claim and what it actually covers (the optical window is the usual weak point).
- Laser class of the module, and the class of the finished system after your housing and optics. A module-level class is not a finished-product certification.
- For 1535 nm modules, read 905 nm vs 1535 nm before you assume the "eye-safe" label removes the need for an assessment.
6. Bench acceptance before design freeze
- Static test at 10%, 50% and 90% reflectivity targets at three distances.
- Dynamic test at the intended update rate on a moving target.
- 30-minute soak at maximum specified ambient temperature.
- Brown-out test at the minimum supply voltage.
- EMC check with the real motor/ESC running.
- 1,000-frame log analysed for outliers and dropouts.
Record the firmware or protocol revision with every log. If a result cannot be reproduced from the log, it is not a result.
7. What to ask the supplier
- Which model revision was shipped, and which document revision applies to it.
- Whether the delivered unit matches the published protocol and electrical table.
- Which fields are calibrated at the factory and which are host-side.
- What the return policy is for evaluation samples.
Model index: https://erdilrf.com/models/. Contact: https://erdilrf.com/contact/.