Arduino UNO R4 Wi-Fi: Unable to List Wi-Fi Networks (Scan Freezes or Returns No Results)

Official Hardware UNO Family UNO R4 WiFi
1

I have an Arduino UNO R4 Wi-Fi board. I’m trying to scan for nearby Wi-Fi networks and list them on the Serial Monitor. Every time I attempt a scan, it either freezes or never returns any networks, even though the board can successfully connect to a known SSID if I provide the credentials.

The UNO R4 Wi-Fi is powered reliably via USB.
The board can connect to a known SSID 2.4Ghz (using hotspot from my phone), so the Wi-Fi hardware partially works.
But once connected (or disconnected), calling WiFi.scanNetworks() never succeeds.

The board prints status messages like “Scanning WiFi…” but never shows the results.
The same behavior occurs even when using official Arduino Wi-Fi scan examples or minimal sketches (the ones from the UNO R4 Wi-Fi library / WiFiS3).
Sometimes the Serial Monitor indicates “Please upgrade firmware,” but after updating the board core, it still gets stuck.

I’ve Tried:

  • Updated to the latest Arduino IDE (2.1.0).
  • Installed the latest Arduino UNO R4 Wi-Fi board core in the Boards Manager.
  • Verified that no older library versions are conflicting.
  • Attempted the ScanNetworks example from the Arduino docs.
  • Tried minimal sketches that call WiFi.scanNetworks() in different ways (including after disconnecting from an AP).The code either hangs at “Scanning…” or returns -1.
  • Tried to ensure the onboard Wi-Fi module firmware is up to date.

Has anyone else encountered scanning freezing on the UNO R4 Wi-Fi with the WiFiS3 library?
Are there known hardware limitations that prevent scanning on this device?
Any recommended official steps to further debug or confirm whether my board is defective?

2

Are any of the networks 2.4gHz? I think it doesn't work on 5gHz.

3

Yes the hotspot I am using is in 2.4Ghz, I can connect but not show it using WiFi.scanNetworks(). I wanted to be able to select the SSID name from the list and press a button to confirm the connection request.

4

Not the core.

The WiFi firmware.

5

Hi @belfagor_000. If you check for the list of Wi-Fi access points using your phone or a computer, approximately how many do you see?

I ask because there is a report that the WiFi.scanNetworks() can hang the UNO R4 WiFi board in an environment where there are a large number of access points:

https://github.com/arduino/ArduinoCore-renesas/pull/387

The allocation of memory for the vector doesn't grow linearly with the increasing of data stored, but logarithmically (view this ) and this can hang up the Arduino UNO R4 board for memory saturation when performing a scan inside an enviroment with many APs.

6

Hi @ptillisch, thank you for your reply.
From my computer I see about 15 access points, but the number keep varying as I am in a office and people can have their personal hotspot and private networks.
I will try again in a place that has much fewer access points.

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