EA4TX – ARS-USB Manual – June. 2024 Page 10
1.6 Connectors J4: Operation of the ADC
The Analog-to-Digital converter (ADC) allows the microprocessor to determine the
direction the rotor and antenna are pointing. To enable, connect the two wires
attached to the azimuth (or elev.) rotator’s potentiometer to J4.
Most rotors use a similar system to read the position in the control unit. The
illustration below offers an overview of this operation:
Inside the rotator there is a potentiometer engaged with the antenna mast axis. The
voltage feedback changes when the antenna is turned. The existent voltage will
change at both ends of the rotation cycle. Normally this will be 0 V at one end
(CCW). The other end will show the maximum value in the rotation cycle. It will be
called “V”. This value depends on each model of rotator optimized for a specific rotor
by the manufacturer. A 500 Ohms linear potentiometer is normally used.
As examples, voltage “V” in a HAM-IV rotor is 12V, in the Kenpro KR-600RC or
YAESU G-2000 it is -3.6V. In some rotors the value is 5V. Again this depends on the
individual rotor.
It is very important to know the voltage “V” provided by your rotator. This
voltage V may not be specified in the manufacturer’s documentation so it
must be checked with a voltmeter for correct operation of the ARS System. If
the Pot is Grounded, you can connect the “V-“ Input at J4 (J4-4 for Azimuth
and J4-1 for Elevation) to Ground at J4-3.
As the ARS-USB board must obtain the voltage feedback from the external Pot, the
two wires that join the control unit with the rotator (the one from the cursor of the
potentiometer and the other from the ground or reference) must be connected in
parallel with the J4 terminals (J4-4 & J4-5). Remember that J4-1 & J4-2 are only
used in elevation rotators.
By this method, the ARS-USB board can read the voltage present at the rotator
potentiometer and thus calculate the beam direction.
The A/D converter has 10 bits resolution. This equates to 1024 possible values. For
example, if the maximum rotation is 360 degrees, a positional resolution of 0.35
degrees is possible. This capability will be more than adequate for most applications.
N
Potentiometer 500Ohms
Control Unit
V
Cable to the
Rotator
ROTATOR
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