I ran into a GPS issue while integrating a TF Mini-S LiDAR into my drone: the GPS just couldn’t get a fix as long as the LiDAR was powered on. Below is a log of what happened and how I traced it down to EMI interference.

Speed spike from GPS glitch
A GPS glitch in the flight log: position jumped so far that the calculated speed exceeded the speed of sound. This is clearly a GPS error, not actual movement.

Symptoms

After mounting a Benewake TF Mini-S LiDAR and a u-blox M8N GPS on the same frame, the GPS couldn’t acquire satellites. I disconnected the LiDAR and the GPS came right back, so the LiDAR was definitely the culprit.

The TF Mini-S fires its laser at high frequency, and that switching noise leaks into the L1 GPS band (~1.575 GHz). It’s a known issue in the ArduPilot community. The symptoms can look like:

  • GPS never gets a fix
  • Satellite count keeps dropping
  • Random GPS glitch errors mid-flight
You need to shield both the LiDAR and the GPS. Shielding just one side isn't enough if they're close together.

Shielding Experiments

Test 1: Baseline with No LiDAR

GPS locked on quickly with no issues. Good baseline: the receiver itself is working fine.

GPS log with no LiDAR and no shield
Figure 1: GPS log for the baseline with no LiDAR connected. Stable satellite count and position.

Test 2: LiDAR Near GPS, No Shield

With the unshielded LiDAR placed near the GPS, the GPS lock became unstable. The LiDAR is clearly the noise source, so shielding it is necessary.

GPS log with unshielded LiDAR near GPS
Figure 2: Testing GPS instability with unshielded LiDAR in close proximity.
Satellite count drop
Figure 3: Satellite count drop observed during LiDAR-on period.

Test 3: Shielded LiDAR, GPS not shielded

Wrapping the LiDAR in copper tape helped a lot, but it wasn’t enough on its own. When I put the shielded LiDAR right next to the GPS, it still caused problems.

So the GPS also needs some shielding. The tricky part: if you shield the GPS, won’t it block satellite signals? The trick is to only cover the bottom and sides. A copper-clad plate mounted under the GPS canopy blocks noise coming up from the LiDAR while leaving the top of the antenna fully exposed to the sky.

Next question: What about the flight controller? It’s also sitting nearby. I tested this in Test 4.

GPS log with shielded LiDAR, no GPS canopy
Figure 4: Improved GPS lock with shielded LiDAR at normal separation.
GPS instability at close range
Figure 5: Residual instability when shielded LiDAR placed too close (GPS canopy also needed).

Test 4: Does the Shield Work Near the Flight Controller?

I moved the shielded LiDAR right next to the flight controller (FC) and toggled it on and off. No issues: GPS stayed stable and the FC behaved normally. The copper-tape shield seems to contain the noise well enough even at close range.

Shielded LiDAR moved close to flight controller
Figure 6: Shielded LiDAR placed close to the flight controller for the interference check.
GPS log with LiDAR ON near FC
Figure 7: GPS log with LiDAR powered ON near the FC. No anomalies detected.

Test 5: Final Setup

LiDAR back in its original position, both shields in place. GPS was stable throughout.

Shielded LiDAR and GPS canopy, final hardware
Figure 8: Final shielded LiDAR and copper-clad GPS canopy in the operational mount position.
Final LiDAR mount on drone frame
Figure 9: Final LiDAR mount under the drone frame with shielding applied.
GPS log, stable in final shielded configuration
Figure 10: GPS log showing stable position throughout the final shielded configuration test.

Flight Test

Took it out for an evening flight on March 18. GPS was solid the whole time and held a fix in both GUIDED and AUTO modes without any glitches.

What worked

Configuration GPS Stability
No LiDAR ✅ Stable
Unshielded LiDAR, canopy unshielded ❌ Unstable
Shielded LiDAR, canopy unshielded ⚠️ Mostly stable (proximity-sensitive)
Shielded LiDAR + shielded canopy ✅ Stable

Wrap the LiDAR in copper tape (or single-sided PCB, copper side out) and add a copper-clad plate under the GPS canopy. Hot glue holds it all together. That’s it.

References

Drone Build Series