Ve6fi Amateur Radio

The above RampDown Timer is used to control  the stopping time on an AlfaSpid Big Rak Rotator that is turning a 5 element full size 40 meter Yagi.  The rotator  is a double worm drive and when the rotator stops, it stops instantly.  However the antenna is still moving at one rev/min and because of the inertia it will want to continue to turn.  If you have a damper in the rotator shaft it will absorb some of the energy but not enough.  This circuit allows the rotator to come to stop in a time depending what you set it at.  I have set it at eight seconds but it is adjustable from zero to one minute. This circuit also has an adjustable ramp up time in software.  I have this adjusted to one second but this is not critical in this operation.  This circuit will not allow you to rotate in the opposite direction until the rotator has come to a complete stop.  Also the reversing relay will not energize until the voltage has dropped to zero.

Basically the circuit is controlled by a PIC that produces a pulse width modulated signal.  It in turns drives the hexfet Q2.  Ian Burn ve6ob, who wrote the software for the PIC, would release the software to interested builders.