Adding ST4 port

[seahawk (Alex)]

Hi all, i have a Celestron Ultima C8 PEC, which i wish to add a ST4 guide port, this can be done through the hand controller, by adding relays as per Shoestring Astronomy circuit diagrams. I was going to "farm" this project out, but after buying the ic/relays & bits i've decided to give it a go myself as i do know some basics.
Ive mounted the ic's, as seen, and the board fits snugly in the Celestron controller box with sufficient room for wiring still. The RJ12 plug will be mounted on a fly lead out. My next task, is the wiring, this is where i'm not 100% sure, the diagram shows Pin 2 on the RJ12 jack as "common" or earth?? but where does it connect in the circuitry, as it is not clearly shown.
Also, anyone with i/c's knowledge, just to confirm the numbering of the pins is counterclockwise from the "dot" end. These ic's fit a 14 pin socket, but only have 8 pins, so i take it the wiring diagram relay pin wiring corresponds to the respective pin on the i/c, if there were the full 14 pins...a little confusing to explain.

Any help/suggestions appreciated !
I am building as per Diagram 1 in the PDF.

PDF is wiring schematics
pics are off my hand controller, both sides of circuit board
and pics of my project, both sides so far, not much, but a start.

cheers
Alex

[wasyoungonce (Brendan)]

Hi Alex, I can help, I'm in Melbourne and have to skills to really bugger this up (Just kidding).

I have to ask why are the interfaces for ST4 using relays? Relays are terribly laggy devices..aka they take time to build coil current and respond to a signal and same when de-energising due to back emf coil current? Is this some legacy or am I missing something?

I think it would be better using an opto Isolator like the 4N25 or 4N28 or even a quad device in the one dil package. See my pic.

In this...when a command is sent to the ST4 jack, the led diode produces a pulse which turns on the transistor making it effectively short cct. The opto transistor is across the handset switch thus...viola a signal is passes like pressing the switch.

Of course a device like all these is and can only give approximations of ST4 commands depending upon how low you can set your guide speed...aka to 1X sidereal.

Anyway see what you think and get back to me.

Brendan

edit:
I forgot ..No charge...only the parts costs (in reply to your thread in the wanted forum)

[seahawk (Alex)]

Hi Brendan, and thanks for your input. I can only summise that relays are used because it may be an old wiring fabrication, of years ago..?? and little demand may have stopped it there..who knows.
The i/c relays are what they've specified, maybe for other reasons we don't know, but hey, if a better solution can adapted, why not i say!

The mount electronics has 4 selectable variable sidereal rates, moon, star, king etc.. It's an old scope, but i like it, it's built like a tank, and very sturdy. I wouldn't mind betting someone with a little ( or LOT) more electronics expertise could adapt a current goto handset to it, as all the electronics would housed in there, the mount drive motors only respond to handset signals i would think.

I've often contemplated updating to a EQ mount, but i think mine still has some good life left in it yet, and i prefer the solid fork mounts.
My main aim is to try out some AP, have qhy5, 20d, all set to try out once i can sort out a guiding issue...

cheers
alex

[wasyoungonce (Brendan)]

Hi Alex. If you have a small PCB veroboard already made up then changing to opto isolators wouldn't be the right thing to do at this stage. I see you can fit this veroboard inside your hand controller.

From what I can see of the handset tracks. It looks as if the white or black wire is ground...but this needs to be measured with a multimeter. Any cheap jaycar meter on DC volts will work.

However...you may not need to connect the ground..from what I can see.

ST4 is "earth switching". It provides an "earth" command (or switched earth....aka a ground pulse) from the guide camera for the relay coils pin 3, 4, 5, 6.

This energises the appropriate relay for what ever the pulse duration is.

So wire it up without the ground and see if it is driving. If you are concerned with not connecting the ground then measure the wires to find ground on the handset and wire the pin 2 ground to this same ground.

Clear as mud?

edit:
and to correct the above image I posted for ST4 earth switching...this would work the other drawing would not because ST4 is earth switching not Vcc switching...sigh.."oh Magoo you've done it again!"