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

J2, the RJ45 connector is for incremental encoders that have differential outputs like those available from US Digital. While it looks like it should work with any of their differential output encoders, we suggest the H6 and T6 series encoders.

The output of these encoders is TTL level differential data. While the CT-2 controller can receive this TTL data directly, due to noise pickup from relays, motors, etc, and strong RF fields, and for lightning protection, the data must be converted to some more robust format before being sent down the line to the controller board. A good way is to use RS485 level conversion.  RS485 is more robust than RS232 and is recommended for longer lines and severe noise or RF environments.  Once the converted signal reaches the vicinity of the controller board, it must be converted back to a TTL level before being applied to the board via J2.

We sell level converter kits for TTL to RS485, see LC485-1 on the Products page for price and ordering information.

Below are details about the converter board and connection to the CT-2 controller.


System Connection Diagram for Incremental encoders

Note: This diagram does not include handling of incremental index pulses. For index pulse info please see the LC485-IDX page.



The cable between the encoders and the LC485-1 can be ordered from US Digital.  Use part number CA-FC5-SH-NC-xx, where xx is the cable length needed.


Connecting to the CT-2 Controller

RJ45 - Input connections for Incremental Encoders
1 Differential input for Azimuth - B
2 Differential input for Azimuth - A
3 Ground
4 Differential input for Elevation - B
5 Differential input for Elevation - A
6 Ground
7 +12 vdc out
8 +12 vdc out

Using the RS485 Converters
Following are schematics and connection information for the LC485-1, RS485 level converters for incremental encoders. This is a dual encoder board which can be configured for TTL to RS485 or for RS485 to TTL levels. Configuration is via a set of 3 jumper pads on the board. Jumper Pad W12 to Pad W13 for TTL to RS485 (using board at the encoder), or jumper Pad W12 to Pad W11 for RS485 to TTL levels (using board at the controller).

The board has two sets of connections to wire to the incremental encoders. Use the J5 connections for the elevation encoder, and J4 for the azimuth encoder.  The J2 RJ45 connector is only used for connecting the board to the controller and it is recommended to leave this connector off the board if the board is to be used at the encoder end of the line.  This will allow more room for attaching the encoder wires.

Below is a reduced schematic of the board.  Click on the schematic to see the board layout and a larger schematic drawing.



Here are the connections from the encoder to the RS485 board
1   Ground
2   Unused *
3   A Channel quadrature data
4   + 5 volts to encoder
5   B Channel quadrature data

* Pin 2 connects to the index pulse line on the US Digital incremental encoders.  There is no provision for this line on the LC485-1 board.  However by adding our LC485-IDX board, the index pulse can be used.  In this case the wire that comes from pin 2 of the connector must be connected to the IDX board and not to J4 or J5 of the LC485-1 board above.  See the Encoders page for more information about using the index pulse.

Specifying the US Digital H6 and T6 series Incremental Encoders
The H6 series encoder is suitable for azimuth or elevation encoding if driven by suitable gearing. The T6 series is easier to use for elevation as it is an inclinometer and will not require gearing (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. A good part number for the Azimuth encoder is a H6-2500-I-S. The part number was derived as follows:

Series =H6, Counts per revolution = 2500, I = Produces Index pulse, S = Single Ended data output.  A good reason to select this unit is because it includes a mounting bracket.  Below is a picture of a similar unit mounted in a housing on the W2DRZ 16 foot dish.

For elevation we recommend the T6-2500-I-S-D inclinometer.  Counts per revolution = 2500, I = produces index pulse, S = Single Ended data output, D = Double Damping.  Double damping is important for an antenna controller as it will significantly reduce display 'jitter' during windy conditions or when starting/stopping the antenna.

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