A device that interrupts a flow of direct current and changes it into pulsating DC. An electromagnetic vibrator consists of an electrical relay whose contacts are held closed by a spring and opened by the pull of the electromagnetic coil. The contacts and coil are connected in series across a source of direct current.

When current flows through the coil, the magnetic field pulls the contacts open and stops the current. When the current stops flowing, the spring closes the contacts and current begins to flow again. The contacts vibrate between open and closed as long as the vibrator is connected to a source of direct current.