ServoCAT ASCOM Driver Help File, June 2015

Several values can be entered on the Driver Parameter Setup window for the ASCOM ServoCAT driver. These values include:

This is a typical Driver Parameter Setup window

A proper serial port setting is required to establish communication between this ASCOM driver and your ServoCAT hardware.

By selecting the proper mount type (Alt/Az, Equatorial, or German Equatorial) the driver will be able to report your correct mount type, if the planetarium software asks for this information.

The ServoCAT ASCOM driver uses your site longitude when planetarium software asks the driver for Sidereal time. The site longitude you specify on the driver setup screen is used along with your computer's time to calculate Sidereal time. Sidereal time is neither read from nor written to the ServoCAT or Argo Navis. Likewise, site location values you enter here are not read from nor written to the ServoCAT or Argo Navis.

In at least one case, planetarium software is known to query the ASCOM driver for observing site latitude and longitude, and then set the observing location to these retrieved values, overriding any other user supplied settings. You are strongly advised to be sure your site location values for latitude and longitude are correctly set in the driver settings screen.

When changing observing site latitude N/S or longitude E/W, be sure the N/S or E/W character is highlighted on the setup screen. Your choice is only selected when it is shown highlighted (displayed with a blue background).

Sidereal time should match the Right Ascension of an object that is on your meridian (due north or south). If you find that your planetarium software is using an incorrect value for Sidereal time, and you have already set the proper site location in your planetarium software, it is possible that the planetarium software is ignoring its internal settings and trying to get the value from the ServoCAT ASCOM driver. If this is the case, then you need to make sure that the proper site longitude is set on the driver setup screen, and you should also double check to see that your computer's time and time zone settings are correct.

If your longitude is West (true for North America), be sure to indicate 'W' on the driver setup screen. When the setup screen is saved, you will see a message window indicating your current Sidereal time based upon your computer time and the longitude that you entered. If you are seeing strange behavior from your planetarium software, you should double check the reported Sidereal time. If you do not wish to see your Sidereal time displayed in a message window when you exit the setup screen, you can turn off this feature by unselecting this feature's checkbox.

With the exception of Serial Port, Site Longitude and Mount Type, other parameters on the setup screen are optional. These values are reported to the your planetarium software, and can be reset by your planetarium software. It is up to your planetarium software to use these parameters.

Warning: If you notice your observing location changing when you connect to your ASCOM ServoCAT driver, this is an indication that the location you specified in the driver parameter screen DOES NOT MATCH the location you have set in your planetarium program. If you are in North America, setting Longitude E instead of W will put you in China! A more minor location jump may indicate that there is an error in site location in lat/lon minutes.

If you enter Aperture Diameter and leave Aperture Area at zero, Aperture Area will be calculated from the Diameter you supplied. The ASCOM Telescope v2 Specification defines Aperture Area as the area of the telescope's aperture, taking into account any obstructions. If you wish to be exactly correct to the letter of the spec, you will want to subtract the area of any central obstruction.

Although the Argo Navis can be configured to do refraction corrections, this has no effect on the RA or Dec values received or sent to your ServoCAT. For this reason, this setting is no longer part of the ServoCAT ASCOM driver parameters.

This version of the ServoCAT driver can be instructed to convert to and from J2000 coordinates if your planetarium program does not speak to the ServoCAT using J2000 coordinates. For most modern planetarium programs, this conversion will NOT be necessary, since they will auto-adjust to the coordinate system used by the ServoCAT driver. In order to enable coordinate conversion, you need to check the box located near the bottom of the driver parameter setup screen.

If this check box is selected, conversion is done from Apparent Coordinates to J2000 without applying refraction correction. Apparent Coordinates are Epoch of Date (EOD), where the ServoCAT and Argo Navis together use ICRS/Airless. At this time, ICRS/Airless most closely matches J2000 with no refraction correction. Apparent Coordinates are not exactly the same as Topocentric coordinates, given that Apparent Coordinates use the Barometric center of the Earth as a reference point. In any event, in order for the ServoCAT driver to convert Apparent <=> J2000, it is absolutely CRITICAL that your Site location coordinates, including Latitude and Longitude, are precisely set for your observing location. Although Site Elevation may not play a role in this conversion, it may be needed for your planetarium program, and is relevant to other coordinate conversions. This conversion will take a few CPU cycles, but should not impose a noticeable delay if you are running on relatively modern hardware.

Please note that one or two message windows may pop up when you are entering values or exiting the driver setup screen. Please be aware that these message windows require clicking the OK button to acknowledge and dismiss the message. This process may or may not work correctly if you are using a remote desktop connection to the computer that is connected to your ServoCAT.

After the first successful connection to the ServoCAT using this driver, the ServoCAT firmware version will be shown on the right hand side of the title bar of the driver setup window, providing your firmware has the ability to report a version string. If the version string is reported, it is also recorded in the driver profile, which is accessible using Programs, ASCOM Platform 6, Tools, Profile Explorer. The left hand side of the title bar of the driver setup window will show the version reported by your ASCOM ServoCAT driver. In the example Driver Parameter Setup window shown above, the driver version shows as ServoCAT Setup v5.2.0, while the ServoCAT firmware shows as SC: v70.A

Please see ServoCAT ReadMe.htm for more details about the ASCOM ServoCAT Driver.

Thanks for using this driver, I hope it helps you go to many wonderful objects!

Peter Eschman,