Tag Archives: lx200

How to upgrade the GPS module in a Meade LX200GPS telescope for much faster GPS fixes

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The 25 year old GPS module in my LX200GPS telescope has great difficulty getting a GPS fix. (My telescope is on a wedge, so the antenna is facing north instead of “up”, plus the backup battery died and is extremely difficult to replace without removing the telescope from the wedge. The biggest reason is that it is 25 years old.)

So I bought a modern BN-280 GPS module ($25) and a $10 USB->Serial TTL programmer, and replaced it. There are some technical details you need to get right to make it work (4800 baud, sending only $GPRMC messages, getting the wires hooked up right) but the overall process is relatively straightforward. Above is my howto video, and below is my big text dump:

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Flashing the One Time Programmable (OTP) eFlash fuses on an u-Blox M8Q GPS to default 4800 baud and GPS only mode

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To issue an One-Time Programmable (OTP) eFlash message in u-blox u-center use the “Messages View” to send specific binary commands to configure or flash the device.
This is done by opening the message view, selecting the CUSTOM type, pasting the command string, and sending it.

WARNING: This is a one time only, non-reversible procedure. After you blow the eFuses with these commands, the M8Q device will ALWAYS default to 4800 baud and GPS only mode on startup. (You can connect to it at 4800 baud and issue configuration messages to change this, but the next time the device is powered down without backup memory power, it will revert to the 4800 / GPS mode only defaults.)

To program 4800 baud default:
B5 62 06 41 09 00 01 01 30 81 00 00 00 00 FC FF 20

To program GPS only mode (disables GSV messages about individual satellites, reducing the total amount of data sent each second):
B5 62 06 41 09 00 01 01 31 81 00 00 00 00 01 05 2C

The above eFlash commands are not published by uBlox (they probably don’t want random people permanently changing the startup default behavior of their GPS units without understanding the irreversible nature of the command) but were provided by u-Blox technical support upon request.

WARNING to LX200GPS users: The uBlox M8Q can ONLY handle 3.3 volt TTL signaling. The Meade LX-200 holds the GPS TX pin high to 5 volts (but uses a level shifter to 3.3v for the GPS RX pin???), which has killed my TX pin (latch up) on a SAM-M8Q unit. So I’m switching over to using a Beitian BN-220 module.

Telescope dolly alignment jigs to repeatedly return to polar alignment

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I want my telescope to be polar aligned when using it. To do this, I need to have the base accurately pointing exactly towards the north pole (in the Azimuth direction) and the Altitude of the wedge the same as my latitude. [This essentially means that I need the tripod base to be exactly level.]

Getting the tripod level is easy, as I have 3 leveling bolts built into the ends of my home built rolling dolly and a bubble level on the telescope wedge.  However, to get the AZ orientation correct, I need to reliably place at least 2 of the alignment bolts in the exact same spots on my patio every time I wheel the telescope outside to use it.

To make this easy, I built these alignment jigs. They consist of a square piece of 2×4 (3.5″ by 3.5″) which rest inside a white square of gaffers tape. The square gaffers tape lets me put these wood base blocks at the exact same point each night. But, I really need to align the 3 leveling bolts, not just the wood blocks. So I designed and printed two 3D printed jigs. One to align the anti vibration puck to the center of the wood spacer block, and one to align the bolt to the center of the anti-vibration puck. The combination of jigs allows me to place the three leveling bolts (and hence, the dolly, and tripod) at the exact same location every night.

You can watch the video below to see how this works in practice.

Focal Reducers f/3.3 and f/6.6 with native Meade f/10 LX200 telescope

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I have a Meade LX200GPS – 12″ SCT telescope, which has a focal length of 3048mm (305mm aperture) and a focal ration of f/10.  This telescope is great for planetary imaging (what I’m mostly limited to, living in a Bortle 7-8 light pollution area, but there exist optical accessories called Focal Reducers which allow you to get this telescope down to a quick f/6.3 or an incredibly fast f/3.3.

I’ve purchased both an Anteries f/6.3 and a Meade series 4000 CCD f/3.3 focal reducer for my telescope, and have been playing around with them and my Sony A6300 crop sensor camera.

f/3.3 Meade Series 4000 Focal Reducer, 10 second exposure, ISO 400


Antares f/6.3 focal reducer, 20 second exposure (unknown ISO, possibly 400)

 

Native LX200GPS – 12 inch f/10, 20 second exposure

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Upgrading the firmware on a Meade LX-200 AutoStar II system

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I recently purchased a used Meade LX-200 telescope, which uses an AutoStar II handbox.  Unlike the  Meade #497 AutoStar controller used on my ETX-125 telescope the LX-200 uses a 6 pin plug for the RS-232 port, and it’s located on the main box, not on the handbox. So if you have a Meade #505 cable (4 pin) it won’t fit correctly. I purchased a Meade #507 cable, which is electrically the same (a RS232 to USB connector) but has the proper 6 pin (larger) plug for the LX200 GPS RS-232 ports.
[Having this cable will also let me control the telescope via software on my computer if I want, so I think it was worth the $20.]


It already had the latest 4.2g (note the lowercase g) firmware from Mead installed (which is good, as Mead is now out of business).  However, I used the starpatch software along with the PatchLX42ggv22.spf and BuildLX4.2g.rom files from the very helpful StarGPS company to patch the 4.2g firmware with a few bug fixes, including the GPS date rollover fix.  [They are very generous in that the trial version of their software will patch all the bugs, although if you want to use it to add in support for a GPS receive to a telescope that doesn’t normally come with it like my LX-200 GPS does, then you have to buy the license key.]


This process took me a full hour of downloading time, because I set the speed to the lowest 9600 baud to give it the best chance of being successful on the first shot. (I ran into issues with my previous firmware upgrade of the #497 handset that was fixed by using 9600 bps.) When it was done, I had the  4.2G (note the uppercase G) firmware installed with patches.  This also enabled the “Smart Mount Technology” option from Meade, which is nice to have available, even if you don’t use it.