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How to test a laser rangefinder module when it arrives

Bench acceptance in an hour, without a calibrated range. The point is not to reproduce the datasheet — it is to find out whether the unit in your hand behaves like the unit in the document.

What you need

• A target board at two reflectances: a matte grey panel (around 10 %) and a retro-reflective or white panel (around 90 %). A painted vehicle panel is a reasonable 30 % stand-in.
• A tape measure accurate over your test distance — the range error you are measuring is metres, so a metre of tape error matters.
• Your supply at the documented voltage, with current headroom for inrush, and a scope or a logic analyser on the interface if you can get one.
• A clear line of sight: indoors, keep the beam off shiny walls and out of windows.

The procedure

1. Power-up. Measure standby and average current. A module that draws twice the documented standby current has a problem before you range anything.
2. Self-test. Most modules report an internal status; record it. If there is none, note that.
3. No-return behaviour. Range into open air or at a wall beyond specification and record what comes back: zero, sentinel or error code. Document it for your parser.
4. Short-range floor. Walk a target in until returns become unreliable. That is your real minimum range, which may be larger than the published figure.
5. Accuracy at three distances. Pick something like 10 %, 30 % and 70 % of the maximum you intend to use. Take 20 measurements each and record mean and spread — not just one shot. A ±2 m module that scatters ±10 m is a different product.
6. Reflectance sensitivity. Repeat at the same distance with the low-reflectance panel. The drop is your real-world headroom.
7. Rate. Run continuous measurement for a minute and count the valid returns versus the frames received. Published "valid rate" figures assume strong returns.
8. Thermal. If the design goes to −40 °C or +70 °C, at least run it warm: a 1535 nm source's pulse energy falls with temperature and the bias of an InGaAs APD drifts.

Recording it

Log distance, target, reflectance, visibility estimate, temperature, supply voltage, and the raw frame for every shot. When a customer later disputes a range, the log is the argument.