OpenSprinkler › Forums › Hardware Questions › OpenSprinkler Pi (OSPi) › How do I connect the RF transmitter? › Reply To: How do I connect the RF transmitter? April 30, 2015 at 1:18 pm #37259 SeanParticipant I’ll try GPIO15. Then de-soulder the relay if it works. In the meantime, can you post all the GPIO that are unused?