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 have only tested with the S2 and T2 series encoders.

The output of these encoders is TTL level differential data. While the CT-1 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. There are two schemes currently developed to do this. One is RS232 level conversion and the other is RS485 level conversion. RS485 is the more robust of the two 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 the Products page for more information.

If you wish to build up your own level conversion, you may choose either the RS232 or the RS485 method. The schematics are presented below on this page.


RJ45 - Input 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

Following are schematics and connection information for building your own RS232 level converters for incremental encoders. There are two schematics shown, first a single one to be used at the encoder end of the line, and second a dual converter to be used at the controller end of the line. If only one of your encoders is an incremental encoder then the dual encoder design can be simplified to only use one set of conversion parts.

At the right hand side of the single converter schematic there are two RJ45 jacks labeled J1 and J2. These are the RS232 level connections that connect to the main line between the encoder location and the controller location. They are wired in parallel, so that one of them can be used as an input from the second board and encoder. Below is a block diagram showing the configuration.

One of these converter boards is required for each incremental encoder, so if you use incremental for both elevation and azimuth, you will need two boards.

The single converter boards need to be jumpered for their intended purpose, azimuth or elevation:

Azimuth jumpers
Normal direction Reverse direction
pad1 - pad 2 pad1 - pad4
pad3 - pad4 pad3 - pad2
Elevation jumpers
Normal direction Reverse direction
pad5 - pad6 pad5 - pad8
pad7 - pad8 pad7 - pad6

To wire the board to the incremental encoder, you can use a US Digital part # CA-1094-1 cable assembly. The pins on JP1 match the wires to the CA-1094 connector.


 

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 block diagram showing the configuration, and a reduced schematic of the board.  A board layout and enlarged schematic is shown HERE.


Specifying the US Digital S2 and T2 series Incremental Encoders
The S2 series encoder is suitable for azimuth or elevation encoding if driven by suitable gearing. The T2 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. For an example, the Azimuth encoder we have used is a S2-2048-B-HS. The part number was derived as follows:

Series =S2, Counts per revolution = 2048, B = Ball bearing,
HS = Sealed housing. Below is a picture of a similar unit mounted in a housing on the W2DRZ 16 foot dish.

The Elevation encoder we have used is a T2-7200.

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