I had been batting my head against the promiscuous sniffer mode of the WINC1500, which seems ideal for my project. Finally I found out why, in the following document revision:http://ww1.microchip.com/downloads/en/DeviceDoc/00002389A.pdf There is in this document revision the following obscure footnote:"14. Wi-Fi Sniffer ModeNote: Sniffer mode is not supported in the firmware version 19.5.x." It seems like Microchip has removed this feature that was earlier provided by Atmel!This was supported in the 19.4.4 firmware and the corresponding Atmel Studio ASF libraries but Microchip has withdrawn the feature, I think because of limited memory on the WINC1500 and the need to better support SSL in the newer firmware. The latest Arduino libraries have of course followed suit.