To be able to test the dual channel up and downlink gateway (see The Things Network dual-channel up&downlink gateway ) we needed to have a node available to demonstrate the downlink messages coming through.
For this, we used a Sodaq ONE which has nice multicolored LEDs we can use to test if the gateway is functioning properly.
I think this is also something that others here can use, so read on here: Sodaq ONE with TTN downlink LED control