On cloudy nights astronomers sleep still do some astronomy, or just something, in order to be doing something. What I did last night: take out my old EQ3 mount — motorized but no goto and no autoguider port — and think about it a bit. After some thinking and measuring, I added a standard ST4 autoguider port to it. While I know there are others who have done so before me, I remember reading some articles a few years back, for this project I didn’t bother to google that/those articles again. Cause it’s not rocket science.

And cause I already have my soapbox driving the HEQ5. Actually I have two soapboxes, so let’s rock.

the steppers used for radec

the steppers used for radec

So I opened the black box the hand controller literally is, to see what’s under the hood.

the top PCB has two buttons and the bicolor LED

the bottom PCB has the microcontroller and those traces there do look like pullup input pins

We know that the ST4 consists of an exposed ground and four pullup input pins. Just looking at the circuit board of the hand controller, it becomes quite obvious that those buttons connect the same way, so let’s measure.

Those traces hint to pullups

Yepp

The next step is to find the physical room for my extension. It’s visible there is no room for a phone connector 6p6c the autoguider is meant for, so let’s macgyver the shit out of the hand controller.

not much room here

the board does have a feeling of being good old, but there is no room

top left corner

There: I exposed the five pins: gnd, ra+, ra-, dec+, dec-

The next challenge is to connect those wires to the top board (cause I don’t want to deep dive into the board underneath, melting away the hot glue and stuff). I decided to add another connector, to not solder the top pcb to a permanent position.

Let’s glue this here.

There is not much room underneath

glued, let’s do the wiring

the cables are all set. Notice how the ground (brown here) got to the center

Notice how I put the ground to the center. At this point I had no idea how to go on with the project, so the two RA’s got to one side, and the two DEC’s to the other. And in the middle: ground. This way even if the pin connector got reversed, nothing really bad would happen.

But in a few minutes I realized that the extension board I’m going to make would solve the keying problem anyway. So: the ST4. I like this guy’s documentation.

the hardware on kevinferrare’s github, the 6p6c (top right) is what we are interested in

So all I have left is to come up with the extension board’s physical size and shape, to house the phone connector. And to connect to my soapbox.

I’m holding a ground and an input pin

When shorted, works as expected

The extension board. I had to add the missing pins to the 6p4c to make it 6p6c, even though the white is not connected

It really starts to fit together

That DC in ??plug?? is from older times, I like it, I kept it

The ST4 driving port on the soapbox

The box is coming together

I don’t like these exposed

Shielded. Amateur astronomy is a rough place

Let’s connect this piece of beauty

There you go

The final touch: duct tape. Problems are made to be solved by duct tape

No big surprise here: it works.