ST4 to Takahashi DIN connector pinout

[rcheshire]

I have a 20 year old Takahashi EM-200B mount to which I would like to hook up ST-4 guiding through the 8 PIN MINI DIN hand controller connector. The mount does not have a guide port and I cannot lay my hands on one of the add on interfaces that Takahashi stopped producing in 2009.

This mount has excellent unguided tracking but I would like implement guiding all the same.

The hand controller does the usual stuff. Hi speed, lo speed, RA and DEC reversal and the RA and DEC pushbuttons.

Below is the pinout. Is this a standard 8 PIN DIN pinout for ST4? In that the pin numbers do not match the 'standard' RJ12 pinouts of which there are two versions. Need to make up a cable RJ12 to DIN.

Another complication is the mount +ve ground circuit. Clearly, interfacing something like a Lacerta M-GEN MII which has a -ve ground seems like an insurmountable problem.

Tak EM-200B Hand Controller Pinout - DIN MINI 8 PIN

1 - HI SPEED SLEW LED INDICATION
2 - HI SPEED SWITCH
3 - +VE GND - Note 2 and 3 connected
4 - RA
5 - RA
6 - DEC
7 - DEC
8 - NC

4 and 5 through RA direction switch to pushbuttons
6 and 7 through DEC direction switch to pushbuttons

[OzEclipse]

Hi Rowland

Shoestring guide to guide port cabling attached.

Joe

[rcheshire]

Thanks Joe. I have it already and guess the question is, having determined that I need to make my own adapter cable, RJ12 to 8 pin MINI DIN, how do I handle the ground connection - and do I need to? The mount side being +ve and the ST4 side -ve. Not sure how it should be wired up. Just keep both sides separate...?

[rcheshire]

Purely out of interest, this is a method of connecting a neg gnd device to a pos gnd system; and all I could find about the subject. Old vehicle enthusiasts.

mgaguru.com

[OzEclipse]

My electronics is way out of date, there may be a better way to do this now. I had a similar problem to this many years ago (1983) when I designed and built a medical instrument. I was measuring the heart muscle impulses (ECG) but then doing signal processing on them using electronics and computers. It was considered highly desirable not to electrocute the patients :D so I had optical isolation between the two. This got me around any problems with varying volatge levels keping the patients safe.

My thought is that you need a box of tricks with something like an optoisolator or equivalent to isolate and invert the pulses feeding the inverted ground referenced +ve pulses into the hand controller connection of the Tak EM 200.

I'd also put in a mode switch (might have to be an 8P8T switch) and connector so you can plug the handbox into and switch into the scope side of your box to control it manually for pointing and centering objects.

Hope that makes sense. I can also ask an up to date expert I know for some advice if you need me to.

regards

Joe

[Merlin66]

Re Positive/ negative grounding....
Is it really a problems which one you use?
The function of the ST-4 is just a open/ close switch between the common line and the directional line.
If the original handcontroller works with directional switching based on a positive then why would the ST-4 type connections (with a positive common) not work the same way????

[rcheshire]

Thanks Joe and Ken. Still getting my head around the problem, which is advanced for me. Appreciate the feedback and pointers.



Ken. The mount is +ve common and the ST4 source -ve common. The ST4 will be a propriety stand-alone guider. The common sources should be connected somehow or so I understand.

Joe. An inverting optocoupler (http://www.jameco.com/shop/keyword=Inverting-Input-Output-Optocouplers) seems to be an option. Would this mean inverting all signals - ST4 and common? I would think so? An up-to-date appraisal would be very helpful.

[Merlin66]

Good point!
I don't know the internal wiring of a guide camera ST-4 which gets it's power from a USB (5.5V) port......

[OzEclipse]

Hi Rowland

I do a lot of fault finding on electronics in my work but haven't done any circuit design work since the 1980's. I'll ask some advice from my friend about the optocoupler approach I suggested and let you know.

Joe

[OzEclipse]

Hi Rowland

I do a lot of fault finding on electronics in my work but haven't done any circuit design work since the 1980's. I'll ask some advice from my friend about the optocoupler approach and let you know.

Joe

[OzEclipse]

Hi

Rowland and I have taken this discussion/ circuit development offline. We are closing in on a working solution using inverting opto-isolators to handle the polarity change. If anyone has an old Takahashi EM200B and wants the auto-guide circuit design we finally come up with, let us know. Anyone wants to participate, let us know.

cheers

Joe

[rcheshire]

This project is nearing completion and was not as onerous as first imagined. Largely a matter of coming to grips with the technology. Thanks to Joe for his ongoing assistance and providing the original circuit diagram.

A working circuit demystified the whole thing. Not so difficult after all.

It is worth noting that the hand controller connector is not a mini din. It is in-fact an Hirose 12 series 8 pin mini circular connector and not cheap - ~70% of costs. The mount socket on the board could have been a mini din, but I chose to go with the Hirose connectors throughout.

That's an RJ45 model - no RJ12 in KiCad that I could lay my hands on quickly.

[rcheshire]

I'll get this up and running in the weeks ahead.

[OzEclipse]

Looks excellent Rowland. You've already tested the prototype, you know it works so now I guess everybody should expect 100% cloud cover in a wide region around Geelong for weeks to come.

You did a great job on it.

Congratulations. :thumbsup: :thumbsup: :thumbsup: :thumbsup: :thumbsup:

Joe

[rcheshire]

Thanks Joe. Really appreciate the help with the circuit design. It was just a matter of creating the hardware.

Still looking around for a metre of 7 or 8 core signal wire cable. Thought was to buy a cheap audio DIN 8 connector cable off eBay and cut it up.

Stand-alone guiding to come...

Yep! It's that time of the year. Not very pleasant. Cold cold cold...

[jwheel69]

Looks great!

[rcheshire]

It works... but the LED switch position indicator shorts the RA- axis. Should have thought that one through with more care. Aside from that it emulates the hand controller perfectly. Now I need a stand-alone guide kit. Looking at the Lacerta MII.

[OzEclipse]

Rowland
Good to hear it's working save the led issue. Maybe run the led off a
buffer if essential otherwise remove it.
Joe

[rcheshire]

Minor flaw.

EDIT: While the ST4 pinout and board connections are correct, I managed to transpose the RA DEC +/- silkscreen for reasons that escape me...!

[rcheshire]

I took delivery of a Lacerta MGENII auto guider last week, prompting redesign of the board. The RA DEC silkscreen is correct after all. In-fact, I managed to invert the RJ12 connector, which needed a little modification.

The latest version of the board is true to the MGEN ST-4 pin out. However, because the Tak has RA DEC reversion (hand controller) and I'm not completely sure which pin is plus and minus (though I feel sure I have that all sorted), I have included RA DEC reversion on the board. Basically, any pin can be set + or -.

Having done all that, the software should compensate and select +/- automatically regardless of physical pin allocation.

Anyway, just to be sure... the board can be matched to the weird and wonderful world of non-standard pseudo ST-4 variations, which is completely irrelevant except to owners of EM200B mounts who want autoguiding... WTS...

Some 3D parts don't exactly fit...

[rcheshire]

Success!

Getting the correct sense of the handcontroller RA DEC reversion switches matched to the adapter made all the difference.

Following polar alignment using the mount's built in reticule, I took a 4 minute exposure with guiding off and then a second with guiding on. It was difficult to discern the difference, without pixel peeping - this mount is superb properly aligned.

Further exposures with high speed correction increasing the rate for subsequent exposures produced no discernable change. Pixel peeping verified the same.

Increasing to 5 minutes verified slight misalignment without guiding.

Satisfied that an operable guider would be confirmed by a series of exposures I set up guiding with normal speed correction on the mount and let it run for 35 minutes.

All seven exposures lined up exactly with beautifully round stars. Will post images once processed.

The Lacerta MGEN II stand-alone guider performed flawlessly with factory settings and a Borg 50mm guide scope.

The EM200B turns 21 this year and has probably never seen an autoguider. It was designed for manual guiding. I'm sure Takahashi had good cause to use +ve ground and Hirose connectors (which are still in production), making the conversion more involved than I would have liked.

[rcheshire]

A crop of the test subject, which does nothing more than show round stars. 5 minute subs. Southern Pleiades, I think. A short video of the alignment of the first and last frames 35 minutes apart.

[rcheshire]

Adding to this, having got everything up and running. There is no auto guiding interface on the EM-200B.

When calibrating the MGEN II auto guider, I noticed that orthogonality and motor speed are linked.

The settings recommended in the attached mount control panel and hand controller images produce 99 - 100% orthogonality, calibrated.

Auto guiding with the MGEN is simple and reliable. Unbelievably so...

The in-built intervalometer and dithering routine has simplified DSLR work exponentially. All in one handset. No computer required - love it...

If you are using a CCD, one of the software packages coordinates dithering between exposures.

[rcheshire]

An update with a few more details on this project. A small how to (http://synergous.com/txtpat/files/TAK2ST4.pdf) for those who have inquired about the 'box'.


This project is licensed under Creative Commons International 4.0 Attribution (http://synergous.com/txtpat/articles/30/task2st4-auto-guider-interface)