Frigoboat, "Merlin II", Automatic Smart Speed Controller for Danfoss/Secop BD35/50F Compressors
 
Merlin II is a small circuit board that plugs onto the controller of your Danfoss/Secop BD35 or BD50 compressor to control the compressor speed automagically!
Includes a green LED that blinks to show at what speed the compressor is running and a red LED that blinks one to five times to tell you were to troubleshoot should your compressor stop for a fault reason.