Absolute Encoders
Note: This is the hardware page for Absolute Position Encoders.  To find complete information on usage of these encoders, please refer to the Encoders page.

J1, the RJ11 connector, is for connection to the US Digital A2 and A2T absolute encoders. These encoders supply absolute position information to the controller board once they are calibrated by setting the range and zero position. While these are the most expensive type of encoders, they are also the best because they never need to be recalibrated unless you change the physical relationship between the encoders and the antenna. Therefore if the antenna position is changed while the controller board is not connected, the controller will still read correctly when it is reconnected.

The A2 encoder can be used for azimuth or elevation with suitable gearing, but it is easier to use the A2T encoder for elevation because it is an inclinometer (works via gravity rather than being driven by a shaft).

To order these parts you must work up the part number by combining the options you want. The web page gives all the particulars. We do recommend the sealed housings to help keep out moisture. For the Azimuth encoder we recommend the A2-S-B-D-M-S. The part number was derived as follows: Series = A2, S = SEI buss, B = Ball Bearing, D = Default shaft extension, M = Includes mounting plate, S = Sealed Housing.

For the inclinometer the part number is A2T-S-D-S.  Series = A2T, S = SEI buss, D = Double Damping, S = Sealed housing.

Addressing: The A2 encoders are normally shipped set to address zero.  This is correct for the elevation encoder but the azimuth encoder must be programmed to use address one.  You can order the encoder from US digital pre-programmed for the addresses you need, or you can buy a USB to SEI bus adapter and software from US digital so you can program the encoders yourself.  However DrzTrack now has absolute encoder programming built in and you can set the correct address, reverse the count direction, and select high or low resolution right from our control program (DrzTrack.exe).  For details on how to do this refer to our software details page.

When you buy A2 encoders, you can order wires with connectors in the length you need (US Digital part CA-MD6-SH-MD6-XX. The connector on the wire kit will plug directly into J1. If you are using the absolute encoders for both azimuth and elevation then you will need 3 of the wires and a 'Y' adaptor (CON-MD6-3J).

The 'Y' combines the signals from each of the encoders. You will need to determine the needed length for each side of the 'Y' as well as the length of the main line.

Alternatively you can buy wire, connectors and a crimp tool for RJ11 connectors and make up the wiring yourself. You will still need the Y adaptor if you are using two A2 encoders.


J1 - RJ11 - Input for A2 Absolute Encoders
1 Ground
2 Busy +
3 Busy -
4 +12 vdc out
5 Data L
6 Data H

Back to Controller