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The Unofficial Temma PC Driver for TheSky


The Unofficial Temma PC TheSky Driver is a software plugin that allows TheSky planetarium software from Software Bisque to communicate with and to control the Temma PC and Temma PC Jr computer controlled telescope mounts from Takahashi. For more details see the ReadMe file.

Release Notes and Instructions: ReadMe file

Download The Unofficial Temma PC Driver (version 0.2)


Temma 2 and Temma 2 Jr. Update: Takahashi has since replaced the Temma PC and Temma PC Jr mount models with higher speed models called Temma 2 and Temma 2 Jr. The command protocol used to communicate with the Temma mounts has not changed so The Unofficial Temma PC Driver works fine with the new models too. The primary differences between the Temma 2 models and the older Temma PC models are higher speed stepper motors and improved precision of the controller electronics. For details see Takahashi Japan's Temma 2 technical report.

TheSky Built-in Temma Driver: Software Bisque developed and is now including their own revised Temma driver for TheSky V5 build 101 and later. The latest TheSky build is available here.

Details on the revised Software Bisque Temma driver can be found here.

It is important use the revised Software Bisque Temma driver included with build 101 and later rather than the version of the driver included with the TheSky V5 build 44 through 100. That driver was problematic.

The advantages of the Software Bisque driver over the Unofficial Temma PC Driver are 1) the Software Bisque driver supports alternative tracking speeds including solar and comet tracking rates; 2) the Software Bisque driver supports fine movement controls from within TheSky (my driver can only support the Jog movement command); 3) the Software Bisque driver automatically gets the Site Location information from TheSky.

Important Note: Even though the new versions of TheSky V5 include a Temma driver you can still install and use my Unofficial Temma PC Driver on the same system. Then you can use whichever driver suits your needs. The Unoffical Temma PC Driver installs as Telescope API driver so it will be listed in the Telescope Setup menu as "Telescope API". The Software Bisque Temma driver has its own entry in the Telescope Setup menu.

Sofware Bisque also now has Temma support built into the latest builds of TheSky Pocket Edition that runs on Pocket PCs running Windows CE. A Pocket PC running TheSky makes a nice portable goto hand controller for a Temma mount.

ASCOM Support: Many astronomy programs now support an independent system of interoperable telescope drivers called ASCOM. ASCOM includes drivers for a variety of telescopes and mounts. There are now a couple of ASCOM Temma drivers available.

Tim Long has developed an ASCOM Temma driver. There is a small fee after a free trial period.

Chuck Faranda has also developed a free ASCOM driver. It is available here:

Information on the ASCOM platform and free platform download can be found here.

As an alternative to these dedicated ASCOM drivers it is possible to use TheSky as an ASCOM driver. TheSky V5 build 100 (5.00.100) or later now includes software that allows TheSky to behave as an ASCOM-compatible telescope driver. Previously you had to purchase Software Bisque's Orchestrate to get this functionality. This driver allows whatever telescope is being driven within TheSky to appear as an ASCOM telescope to ASCOM-host programs like MaximDL/CCD. This functionality works with both The Unofficial Temma PC Driver and with Software Bisque's Temma driver. Just install the ASCOM platform. Select "TheSky controlled telescope" as your ASCOM telescope driver from within your ASCOM host program like MaximDL/CCD.

USB Support: Many laptops no longer include RS-232C serial ports. Instead they provide USB ports. It is possible to use a USB to serial adapter to allow newer laptops to communicate with the Temma mounts. I have successfully used such devices from Keyspan and iConcepts under Windows XP.

The Temma Command Protocol: The command protocol for the Takahashi Temma PC telescope has been published by Gene Horr with the assistance of Texas Nautical Repair. A PDF file documenting the protocol is available here.

Source Code to The Unofficial Temma PC Driver: Most of the source code to the Unofficial Temma PC Driver can be requested by sending me an email to richardl * at * well * dot * com. I ask that you don't sell the driver or derivative products.

Takahashi EM-10 Temma PC Review

The Takahashi EM-10 Temma PC Jr. slews at up to 150x sidereal rate. Where this is most noticable is for mount flips when the scope crosses the meridian. On my Temma PC Jr. a computer controlled mount flip can take five minutes! But if I'm in a hurry I just release the clutches, move the mount and re-sync on the other side of the sky. (The EM-10 is only available in the Temma PC Jr configuration, but the EM-200 is available in either 400x Temma PC or PC Jr. models and the NJP is only available as 400x Temma PC.)

The upside of this relatively slow slewing is that Takahashi has not sacrificed the performance of their low speed guiding. I really can't argue the pro and cons of stepper motor vs servo motor mount designs, but suffice to say that the precise guiding that Tak mounts are famous for remains intact. (The EM-10 uses stepper motors by the way.)

The Temma PC Jr. currently requires the use of a PC for goto control. The Temma PC mounts connect via RS-232 to a Windows PC.

The hand paddle attached to the mount still works when the mount is connected to the PC.

The EM-10 is an open-loop system meaning that it will lose goto sync once the clutches are released. There are encoders built into the system, but these encoders are located on the worms so they only measure driven mount movements.

The Temma PC mounts come with a planetarium program called Telescope Tracer 2000 (aka Pegasus 21). It's a simple program capable of controlling the mount. But its database is quite limited and it is missing many features that anyone used to TheSky will sorely miss. Another planetarium program called Kagayaki III from Seedsbox ( ) is available and will drive the Temma PC mounts. Kagayaki is a no nonsense planetarium program with an emphasis on ergonomics.

Enter the need for a driver for TheSky. The reliance of the Temma PC system on these two programs was it's single largest shortcoming. Now that I have written a driver for TheSky (available here), I must say that the Temma PC system works quite well. I can take advantage of the integration between TheSky and CCDSoft which is very nice. The Temma PC system design is quite straight forward and flexible and should be easily supportable in the future with any needed drivers.

The Temma PC system relies on the polar alignment of the mount for goto accuracy. (Unlike some GEM goto systems like the Vixen SkySensor 2000, Temma PC is only designed to work in an equatorial configuration. The Kagayaki III software mentioned above does offer a mode where it can drive the Temma PC mounts in a non-equatorial mode where the situation may demand it. But this is not useful for long exposure imaging.) Most typically the mount must be polar aligned (it is generally agreed that Tak polar scopes work very well), the goto system is then synchronized with one star and that's it. Like any goto system the mount can be resyncrhonized as you go on.

I measured goto accuracy using my EM-10 with a just good polar scope alignment (no drift alignment) and a Vixen GA4 illuminated guiding reticle. Goto was always within 5 arc-min and typically within 2 arc-min. With a mount flip it was under 10 arc-min. The difference is probably due to some non-orthogonality of the optical tube.

The Temma PC and PC Jr mounts come with an autoguider cable that is directly compatible with the DB-9 connector on ST-7-type cameras. (Additional cable and relay boxes are no longer required as they were for previous Tak mounts.) But the DB-9 connector on my cable had to filed down to actually fit on the ST-7E camera. An adapter cable is required for the phone-type connectors on the STV or SBIG color filter wheel. But such a cable can be easily constructed.

The Takahashi mounts do not support PEC training. But the periodic error of my EM-10 measured to be smooth and well within the specification of 10 arc-seconds. The worm period is approximately 10 minutes. So autoguiding should be able to address this.

One unusual aspect of the Temma PC mounts is that they will run on either 12V or 24V DC power. But 24V is required for their "high speed" slewing support. I drive my mount off a 24V "wall wart" style AC adapter in the backyard and in the field off two 12V gel cells wired in series. The EM-10 draws up to 2.5Amps at 24V with both motors slewing. Average power consumption is under 1 Amp at 24V.

Another unusual thing about my EM-10 Temma PC Jr. mount is the noise it makes when slewing at high speed. This sound can best be described as something like a jet airplane noise (but at far lower decibel levels).

The standard adapter plate on the EM-10 is a Tak two hole design which fits Takahashi clamshell tube holders. I found the Tak clamshell system lacked sufficent range to properly balance the short Sky90 OTA heavily backloaded with a ST-7E CCD camera, color filter wheel and motorized focuser. So I replaced the standard Tak adapter plate with a Losmandy-compatible Astro-Physics DOVELM saddle. (Astro-Physics sells and EM-10 adapter.)

Overall, I'm a big fan of my Temma PC Jr EM-10. I chose this mount as part of an "ultra-portable" imaging system. The EM-10 Temma PC Jr fits this bill primarily because it combines the precision features needed for imaging with light weight needed for portability (the head weighs 24 lbs. including counterweight). I'm using this mount mostly with an ST-7E and a Tak Sky90 refractor. But I've also used a C8 on the EM-10. The EM-10 and Sky90 can each be packed into a 1500 pelican case.

As for value, that's harder to deterimine. Probably the mount closest in features and capabilities to the Temma PC Jr EM-10 is an Astro Physics 400GTO which has a similar price, but much more limited availability.


Content updated Dec. 15, 2003