You don't need to build your own interface.
I control my Takahashi EM-200 with Sky Safari on iPad using a SkyFi interface. It works brilliantly.
The EM-200 is the Takahashi version of the
EQ-6 mount but does have different (simple) electronics and connectivity.
I use the Simulation Curriculum Sky Fi interface. Simulation Curriculum also are the company that produce Sky Safari. My experience has been that the two products work together very seamlessly.
https://www.simulationcurriculum.com/pr ... ories.html
https://www.skysafariastronomy.com/skyf ... ntrol.html
When you order, you need to order the SkyFi, and the appropriate serial or USB cable for your particular telescope mounting make and model or series.
They are compatible with most mounts including the Orion Sirius mounts. There is a compatibility table on the web page I linked.
I have been using mine for 5 years. The inbuilt rechargeable battery still lasts all night without any auxiliary power. Recharges from USB so field recharging off 12V is easy if the battery starts to wane.
The only downside for my setup is that Sky Safari on its own, only supports a one star alignment. This means that my
EQ mount needs to be accurately polar aligned. When I put in a question to the manufacturer about this, they (not knowing I had an EM-200) told me to use the two star alignment in the handbox and the Skyfi and Sky Safari would make use of that. I assume that you can do this multi star alignment in the Orion handbox. This is more of a problem for me because my EM-200 has no smarts in the hand control. Just a few slew buttons. I have a quick accurate way of polar aligning. In the southern hemisphere, we have two Mag 7 stars a few mins either side of the south celestial pole. In the northern hemisphere, you don't have any stars near the pole but you should be able to use the Orion two/three star alignments to make your pointing model. Once my scope is accurately aligned, pointing works well even after a flip.
I haven't quantitatively tested pointing accuracy. It's accurate enough for me to put objects about 0.1-0.15 degrees from the centre. Easy for the prime focus frame of my Vixen Cassegrain with a
DSLR camera (1280mm focal length) although this is also down to the mount and encoders. Also accurate enough for the scope with a 10mm 65 deg eyepiece. I mostly use the Vixen for astrophotography.
When I was working full time and would head out during the week to a friends dark sky property, I would set an intervalometer to capture 400 subs 2 mins each. I would nap in the car while doing photography with a 300mm ED telephoto. I would set an alarm every couple of hours, wake and without even getting out of the car, I would change targets on the iPad. One or two subs would be trailed in the process of slewing to the new target. Then it would point to the new object and keep going. I would only get out if the object was large and needed careful framing.
Sky Safari is easy to use. Setup of the interface is pretty quick. You need to ID the port number in settings and the mount type. It helps if your Sky Safari device has a GPS but I think you can enter location manually.
A Sky Fi costs quite a bit more than the device that Jim recommended but it works well. Doesn't seem to mind the dew either.
I don't think you can set up acquisition sequences of multiple targets. For that you need one of the more advanced packages like MaximIDL or similar.
good luck
Joe
Amateur astronomer since 1978
...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships Astronomical Association of Queensland; RASNZ Occultations Section; Single Exposure Milky Way Facebook Group (Moderator) (12k members)