Flasher type fish sonar

A flasher type fish sonar comprising:

• an ultrasonic vibrator for transmitting ultrasonic waves in water and for receiving reflected signals in the water, a transmitting circuit for supplying oscillating signals to the ultrasonic vibrator, a receiving circuit for amplifying reflected signals received by the ultrasonic vibrator, an analogue to digital converter for converting the reflected signals to digital signals, an input circuit for inputting the digital signals from the analogue to digital converter through a control circuit, a flasher display including:
• a rotary disk having a luminous body mounted on the rotary disk and rotated by a motor, and a display board having a window displaying luminosity of the luminous body by inputting the digital signals from the input circuit through brushes connected to the input circuit and slip rings mounted on a rotary shaft of the rotary disk, the slip rings being contacted with the brushes, and a constant current circuit in the input circuit such that a change of electric current flowing to the luminous body due to contact resistance between the slip rings and the brushes is eliminated by the constant electric current from the constant current circuit.