An ST4 autoguiding port is a must for astrophotography, but most of the time, this port is only available on big and costly mounts. The chinese EQ4 and EQ5 aren't perfect, but they perform well with decent payloads. Sadly, they don't provide such a port, except with very expensives GOTO systems.
The ST4 port principles are very simple. One wire per direction, meaning four wires, plus one common wire. If you connect a direction wire with the common wire, the mount moves. It can't be simplier. The EQ4/EQ5 dual axis motor drives perform well. The handbox use a micro-controller to stepper motors. We just have to connect our ST4 wires to the handbox buttons, and we have an autoguided mount !
What do you need :
- Tools :
- A cruciform screwdriver
- A small plier
- A cutter
- A soldering iron
- Parts :
- An RJ12 female socket
- 5 small wires
Get some free space for the connector :
There is many ways to do this mod. Often, the connector is out of the box.I wanted to put the connector inside the box, in order to reduce the amout of wires. The handbox is almost full, but there is a bit of free space int the bottom left. This space is used by long screw which can be reduced.
We will have to cut a window in the hanbox body. See the picture (red sides) :
We will also have to remove some plastic on the cover :
Be carefull. The cotations may change, depending on your RJ12 socket.
Pins assignement :
The RJ12 ST4 pin assignement is described on the following picture :
You will have to solder a wire on each pin from 2 to 6.
Soldering on the PCB :
Our ST4 port will act as the handbox buttons. So, our wires will be soldered on Buttons pads. The following picture shows the button's PCB back side, with all the solder spots.