HOWTO: Upgrade the GPS unit in a Meade LX200GPS telescope for extremely fast GPS fixes

Parts & Detailed Instructions: 1. Beitian BN-220 GPS Module TTL w/Flash NMEA-0183 9600bps 1Hz for Arduino RC FPV Drone Flight Control $24 Amazon Affiliate link: https://amzn.to/3M9GxxR 2. FT232RL USB to TTL Adapter for Development Projects, USB to Serial Converter with Genuine FTDI USB UART $10 Amazon Affiliate Link: https://amzn.to/3ZynzEx 3. I bought my female JST SH 1.0mm pitch connectors for $0.95 each at Sparkfun (but had to pay shipping). Update: If I were to do this again, I'd buy this breakout board with the 6pin JST SH connector on it to make the job much easier: https://www.pololu.com/product/4773 You can also get them on Amazon, for example this 20 pack comes with male connectors with wires, and the same surface mount female connectors that are a bear to solder to: 20 Pairs Mini Micro 6 Pin JST SH 1.0mm Cable Connector, JST SH 1.0mm Pitch 6 Pin Male Female Connector Plug with 150mm 26AWG Wires Cables, for LED Strips Lights, RC Toys, Batteries $10 - Amazon Affiliate Link: https://amzn.to/4qYaIYe The Beitian BN-220 GPS unit has a 4 pin header, and provides 3 sets of cables that plug into it (1 male pins for a breadboard, 1 female sockets to go over pins, and one double ended connector which you can cut off to solder to your own things) Pinout from left to right is: 1 - Black Wire - Ground 2 - White Wire - GPS TX 3 - Green Wire - GPS RX 4 - Red Wire - + 3.3 volts to 5.0v power The BN-220 unit is capable of 5 volt TLL signaling on the RX/TX lines, which I believe is important, because another unit that I tried which only does 3.3 volt signaling failed in my testing. [I can't say for sure it was because the telescope RX line is pulled up to 5 volts (at very low current) but that is the only thing I can think of that would have caused the UART line to fail the way it did.] U-Blox software settings: Baud rate is 9600 by default, so you need to change it to 4800 at Configure - PRT (ports) 4800 Configure - RATE (rates) - 1 sec (default, works for limited messages) 3 sec (may work without limiting messages, not tested) The Meade LX200GPS REQUIRES the $GPRMC message. [It ignores any others.] NOTE: The newer BN-220 defaults to a "GN messages (Global Navigation) instead of GP (GPS) messages, which the LX200GPS won't recognize, so to change this to GPxxx messages (USA GPS default, vs global GNSS default) you need to changes the "MainTalkerID" to GPS so it will produce the messages that the LX200 is expecting. Config- NEMA- MainTalkerID to 01-GP (GPS) After you make the changes, you must also save them to flash memory so that the unit starts up with the correct configuration after power is lost. Configure - CFG (Configuration) - Save current config (bbr/flash + I2C & SPI for safety) HOW TO LIMIT UNNECESSARY MESSAGES: Instead of changing the rate (which worked for others, but I haven't tested), you can reduce the amount of data that is sent so 4800 baud works fine at the 1 second refresh rate. To make it work at the default 1 Hz rate, I disabled all of the extra NEMA packets that the telescope doesn't look for or need (GGA, GSA, GSV, VTG). We NEED the $GPRMC messages for the telescope (but nothing else) Can Disable: GGA, GLL, GSA, GSV, VTG To do this, you go into Config - MSG (Messages) And then select each of the following and uncheck all the checkboxes (clicking send for each message) F0-00 NMEA GxGGA F0-01 NMEA GxGLL F0-02 NMEA GxGSA F0-03 NMEA GxGSV (This one reduces the most bytes....) F0-05 NMEA GxVTG You leave ONLY the F0-04 NMEA GxRMC message enabled. This allows the telescope to easy process the $GPRMC message as there is a lot of "down time" after it gets sent each second. Of course, you still need to save all of these configuration changes to FLASH so they persist across reboots. Configure - CFG (Configuration) Save Current Config (I selected the I2C and SPI flash options in addition to the default BBR/Flash/Eprom ones, as I'm not sure if the BN-220 module has built in flash, or if it uses a separate I2C or SPI flash chip, so I figured it was best to attempt to save everywhere, and it doesn't hurt.) After this, I confirmed that the BN-220 GPS unit works when powered by the telescope and the LX200GPS successfully gets a GPS fix from it. The minimum set of wires needed for the telescope to get a GPS fix is: +3.3v, GPS TX (to Telescope RX) and Ground wires. Looking at the front (plug in side) of the connector that comes out of the top fork arm (or looking at the back of the receptacle I purchased to plug into it) the pins to use are: Far Left: Ground [GPS black wire] Not Connected (Battery Backup?) Not Connected (GPS RX/Telescope TX, measures 3.3 volts when telescope powered up) (GPS green wire) GPS TX / Telescope RX (Measures +5 volts when telescope is powered up!) [GPS white wire] Not Connected (Enable line?) Far Right - +3.3 volts power [ GPS red wire]