The GPAS mk2 interface for GPS units & GOTO telescopes

[The following assumes that you are familiar with the ‘plain vanilla’ operation of your telescope, using manual (i.e. non-GPS assisted) alignment. You should familiarise yourself with the manual operation of your telescope before using the GPAS box]

• Physically set up and align your telescope (or Autostar) and plug the telescope (or Autostar) serial cable into it.

• Plug the serial data cable into your GPS receiver, site it near the telescope and switch it on. Ensure GPS is set to send NMEA-0183 data.

• Plug the serial cables from the GPS and the telescope (or Autostar) into the GPS and Scope ports of the GPAS box.

• Switch on your telescope.

On the Autostar hand controller, go past

Then press ENTER or MODE three times to get past

• Switch on the GPAS box, (red LED will come on steadily). When the GPS acquires satellite signal lock and sends valid data, (LED will flash rapidly) it will update the telescope (or Autostar) Following this update the LED will blink slowly (showing that GPAS has gone into a low power hibernation mode)

That’s it! Your telescope’s (or Autostar’s) currently selected site will be set to the correct latitude, longitude, date, and UTC time. (Check it and see!). You may now use your telescope and use the GOTO functions with great precision.

If you wish to repeat the GPS update, switch off the GPAS box. Wait momentarily, then switch it on again. It will now repeat the update of the telescope (or Autostar).

NOTE: Meade®, Autostar®, Garmin®, Magellan®, Trimble®, GPAS® are all registered trademarks and all rights are reserved by the respective owners.

Congratulations on your purchase of a GPAS® interface box. The GPAS is the most elegant solution available for GPS enabling your Meade® GOTO telescope. It was designed by an astronomer for use by an astronomer outside, at night, in the dark! Only a diffuse red light is used on the box to avoid compromising your dark-adapted eyesight. BEWARE of any astronomical products that use multi-coloured lights. These coloured lights can compromise your dark adapted eyesight, and thus your ability to see faint objects.

The GPAS allows you to maximise the benefit from your investment in a GPS receiver: You can use your GPS receiver normally and also use it to synchronise your telescope. You have saved money on GPS enabling the ‘scope compared to buying alternative GPS ‘embedded’ products. (If you already have a GPS, why buy another one, that’s tied to the ‘scope?). You do not have to modify the software in your GPS receiver or telescope or Autostar® controller. You can use the GPAS on multiple scopes e.g. if you own more than one, or at a star party to GPS update everyone’s Meade® compatible telescopes. No special software, modifications or licences are needed.

The GPAS contains two serial circuits (RS232 / DTE) which emulate two separate PC serial ports. The GPS receiver outputs data in a different protocol and at a different rate from that used by a Meade® GOTO telescope. The GPAS intelligently translates this data using an in built microprocessor, and transmits it to the 'scope so that your scope will have an accurate fix of position and time (to GPS accuracy).

To use the GPAS interface you will need:

1. Meade® GOTO telescope (e.g. LX200, LXD55/75, LX90 or similar or any Autostar® 495 or 497 controlled telescope.
2. A serial cable of the type used to connect your telescope to a PC serial port. (supplied as an option with the GPAS) (e.g. Meade® #505 or #07047 cable set)
3. GPS receiver capable of outputting NMEA 0183 serial data stream (this is practically every GPS receiver sold in recent years).
4. A serial cable (supplied by the GPS manufacturer) of the type used to connect the GPS receiver to a PC serial port.

Place a new PP3 (9Volt) battery in the compartment at lower rear of the GPAS box, taking care to connect the battery with the correct polarity. Test the box by switching on the GPAS, and ensure that the light on the front of the box illuminates. Switch off the GPAS again. (To avoid damage from a leaking battery, remove the battery from the GPAS if it is not to be used for a long time)

Switch on your GPS receiver and go through its configuration screens to find the communication option to switch on NMEA output. Select NMEA-0183-2.X (where X is any number) protocol. (See documentation supplied with your GPS receiver, or manufacturer website.) Check that your GPS serial cable fits and works! If in doubt contact the seller of your GPS receiver.

Please be aware that, in use, the GPAS box will overwrite the currently selected site in the Autostar or 'scope with the current latitude and longitude as determined by the GPS receiver. (You should change the selected site on the Autostar or 'scope before using the GPAS if you wish to prevent a particular site’s data being overwritten)

TIP: On site, you will be probably be working in the dark. It is fairly easy to inadvertently disconnect the serial cables from the D type connectors of the GPAS, unless you use their grub screws to secure them… This can lead to unnecessary frustration: It is suggested you use the screws to secure the D Type connectors (but of course, this is entirely optional).

Switch on the GPS receiver and connect the GPS receiver to the GPS port of the GPAS box, and ensure that the GPS has an unobstructed view of the sky. (The more satellites the GPS receiver ‘sees’ the greater the accuracy of the position fix).

On an LX series telescope the GPAS is connected to the RS232 port on the 'scope base, on a telescope with a #495 or #497 Autostar, the GPAS connects to the Autostar itself. Connect the Autostar® controller (or GOTO telescope) to the port labelled Scope on the GPAS box, and follow the usual procedure for aligning the ‘scope in the home position (level tube pointing due North/South etc, see ‘scope handbook). On the Autostar® controller press the MODE button repeatedly to pass the sign on screens without entering anything, until you reach the ALIGN prompt, and the Autostar display dims.

(i) Switch on the GPAS box: The red light on the box will illuminate. The GPAS box is now waiting for the GPS receiver to find and synchronise with the GPS satellite signals.

(ii) When the GPAS box successfully receives a valid update from the GPS receiver, the light will flash rapidly. The GPAS will immediately start to update the telescope

(iii) When the telescope is updated, the GPAS will go into a low power hibernation mode and the light will slowly blink - this helps you find it in the dark, but it is also useful in the field to leave it on, blinking as a beacon to help avoid someone walking into your scope!

• You may now switch off the GPAS box. (You may also switch off the GPS receiver, unless you are going to synchronise another ‘scope, in which case it will save time if it is left on).

• The GPAS box can now be disconnected from the ‘scope and stored away until needed again. (Or left connected as preferred)

That’s it… the ‘scope / Autostar® has now been set to exactª latitude and longitude of the observing site, and has been set to the exactª date and UTC time (ªas determined by GPS receiver data).

If desired, you can perform as many updates as you wish at any time by repeating from (i) above (please count two seconds between switching GPAS off and then on again to allow the internal microprocessor to reset. If the light is not illuminated steadily, then it has not reset) Please ensure that the GPAS box is switched off when connecting it to a telescope, Autostar® controller or GPS receiver, and switch it on after it is connected.

Troubleshooting:

# The light is not on when I switch on the GPAS box:

• Ensure that battery is good, that you allow two seconds between switching GPAS off and on again. (this interval is to allow a complete reset of the microprocessor)

# My telescope (or Autostar) is not being updated at all:

• Is your GPS set up to send NMEA0183 data? This is usually set to ‘off’ by default, and you will have to go through the GPS instruction manual / GPS set up screens to find the communication option to turn it on.

• Check that your serial cables are working by connecting them between a PC and the equipment. Run up Hyperterminal and check communications through the cable. Most GPS receivers set to NMEA mode sends a data stream continually at 4800-N-8-1 as soon as they are switched on, but some types of GPS receiver do not send NMEA data when there are no satellites visible.
• The Autostar sends an ‘X’ at 9600-N-8-1 when it is powered up. LX200 / Autostar should respond with ‘scope model if you type in carefully (case sensitive, no spaces) # : G V P # <enter>

• Does GPAS light stay on? If so, then GPAS is not receiving valid data from the GPS receiver (either GPS has not locked onto satellites yet, or cable from GPS may be faulty or no NMEA data stream - see above)

# My site’s latitude is not being updated (but longitude, date and time are updated)

• There is a known issue with Meade’s Autostar software versions 27G & 30E that prevented latitude data being accepted. The easy way around this is to update the Autostar software up to the latest version using the freely available MEADE ASU programme. (see www.meade.com)

# I Keep getting the Sun warning / Getting Started message on my Autostar

• Once you understand this message: To automatically skip past the sun warning (and the "Getting Started" message) you can use the Autostar

MODE Þ Utilities Þ Display Options to set the following as defaults:
Utilities Þ Display Options Þ Sun Warning Þ OFF <enter>
Utilities Þ Display Options Þ Getting Started Þ OFF <enter>

# My GPS receiver doesn’t communicate with my PC anymore

• Because you set the GPS receiver to NMEA mode to operate with the GPAS, you will have to set it into PC communication mode to communicate with a PC. Terminology varies here, but typically, it will be available under the GPS receiver setup screens as "Garmin mode" or "RS232 mode" or similar (See your GPS handbook). Remember to set it back to NMEA mode for use with the GPAS.

# Other problems

• In case the above suggestions do not solve your GPAS problem, check all batteries are good, re-check RS232 serial cabling and consider resetting your Autostar, via the screens SETUP – RESET (N.B. you will need to retrain the drive motors if you take this step).
  

• Read through this set of instructions again, and if you are still having trouble, contact the maker of your GPAS unit for further advice (info@botsky.co.uk)

The GPAS box is warranted against all manufacturing faults for 3 years, and it will be repaired or replaced (at manufacturers decision) free during this period. Faults arising in equipment connected to the GPAS are not covered, irrespective of cause.