Return to Home Index
Return to Electrical Index
Return to Plug Cable Details

Miscellaneous Information About the LX200 Classic Ports

A number of ports on the LX200 control panel are described below.  In some cases these are not clearly described in the instruction manual.

There is a port labeled AUX.  This port was originally designed to be used with encoders which were available for the LX200 many years ago when it was introduced.  When the encoders did not sell, they were eliminated and the port was relabled AUX.  A very modest power is available from this port.  It only provides +5 volts at some unknown, but modest current.  I believe that a modest logic circuit could be operated from it if it required only tens of milliamps. There is no other known use.  The signals which might be available at this port are undocumented.  They seem to be logic level input and output signals such as one would expect from standard encoders.

There is a port labeled RS232.  This is a standard 232 port but it contains connections for two 232 ports.  One is connected with the standard 232 cable which in turn connects to a computer. To use both of the ports, a special cable must be made up.   The connections for this cable are as follows.   The pins are numbered from the left to the right looking at the front of the LX200 control panel.  (Note this is NOT the strange numbering shown in the Meade operation manual.)

pin  1    +12 volt power
pin  2    Ground   Note that this ground is not the same as the return power socket ground, there is a 0.1 ohm resistor which is used to measure power supply currect between the two and thus some 0.05 volts potential.
pin  3    Misc. Transmit
pin  4    LX200 Transmit
pin  5    LX200 Receive
pin  6    Misc. Receive

The normal LX200 transmit and receive lines go to the computer receive and transmit lines.  The second set of lines on pins 3 and 6 then can go to another serial port on the computer.  They go to the computers receive and transmit pins respectively.  DB type connectors which connect to most computers are either DB9 or DB25 types which fit the serial connectors on the computer.

Modular plugs and the necessary crimper as well as wire are available from electronics supply houses such as Radio Shack or Newark Electronics.

There is a port labeled Focuser.   This port provides power to the Meade focuser with two speeds controlled from the keypad.  It might be noted that the low speed works ok if the telescope is powered from 18 v but may not work for 12 v.  Some other, non-Meade,  focusers will also work from this output.

There is a port labeled Reticule  This port provides both variable intensity and blinking modes for the Meade 9 mm illuminated eyepiece.  (or similar eyepieces)  Note that the ground terminal on this connector is not at the same potential as the return ground on the power supply socket.  There is a 0.1 ohm resistor between the two which is used to measure the power supply current.

There is a port labeled Keypad.   This port of course goes to the Keypad.   The keypad should not be plugged in or unplugged when the telescope power on.  Permanent damage can be caused to either or both the keypad and computer boards.  Excessively long cables, greater than 50 feet, should not be used unless a heavier ground wire is supplied.  The four wire cable carries ground, power to the keypad and the two signal lines.  The signals to and from the keypad are serial digital signals.  These are discussed in detail elsewhere on this web site.

There is a port labeled Power  On earlier telescopes this port was labeled 12 volts DC.  It is now labeled 18v DC.  The scope seems to work with 12 volts but the higher voltage is recommended by Meade so as to get full power out of the drive motors.  Note that the return line from this socket is not at the internal circuit ground.  There is a 0.1 ohm resistor between the socket return connection and the internal ground which is used to measure the power supply current.

There is a port labeled CCD which is to be connected only to a CCD imager to control the telescope in the guiding mode.   The cable for this connection is special.  One of the wires in the cable must be cut or a connector pin removed and the cable itself is reverse order from a normal 6 wire cable.   Take great care to use the correct cable.

It is not only possible but convenient to guide the LX200 through the CCD port.  The PEC training of the worm irregularities can also be done through this port.

In order to do this a keypad must be made which has four momentary switches.  The CCD port takes a standard 6 pin modular plug.  This is connected to a standard 6 wire telephone type cable and four momentary switches are connected between the four control lines and ground.  The control lines are normally high (+5volts).  The N, S, E, W motions are activated by shorting one of  the four control wires to ground through one of the momentary switches.  The pins in the socket are numbered from the left to the right looking at the front of the LX200 control panel.  The keyway is to the bottom and the pins in the socket at the top.   These pins correspond to the following connections.  Note this is NOT the strange numbering used in the Meade instruction manual.

pin  1   Do Not Use (do not connect external wire)
pin  2   This is the Ground pin  Note this pin is not at the same potential as the return groun for the power supply for reasons described above.
pin  3   This is the WEST motion pin
pin  4   This is the SOUTH motion pin
pin  5   This is the NORTH motion pin
pin  6   This is the  EAST motion pin

A wire of almost any desired length can be used.  Mount the four momentary switches on a small control box and connect the wires to the switches in the order suggested above.  Connect the other side of each of the switches to ground.  The control box can be a small plastic box like those found at Radio Shack.  Switches can also be found there.  The 6 wire cable can be made up by attaching a modular plug to a length of cable if you have the crimper tool.  Otherwise, a 25 foot extension cord can be used with one end cut off and stripped back appropriately.  The advantage of using the CCD port is that the keypad is very simple to construct.

There is a port labeled Dec Motor which takes the  cable that goes to the declination connector on the fork.  Note that there is a second connector on the inside of the fork which should be checked from time to time to avoid intermittent circuits.  The wires in this cable carry the power to the motor, the power to the demodulator circuit board on the declination drive and the encoder signals from the encoder wheel to the computer.
 

Return to Beginning

Go to Home Index for Doc G's Info Site