Adding a 2nd Serial connection
via a Modem-to-Modem link
as of Feb 18, 2002
I have discovered the fun of using a separate laptop that is running a planetarium program (like Earth Centered Universe) to control my telescope. The "nominal" configuration for doing this is via a null modem cable. Click here for an example layout.
Why add a second serial connection?
I use encoders with my telescope mounts since the gearing I use for the drive systems results in very slow slewing. Slow slews are OK for short slews, but tedious for longer ones. So, I simply declutch, manually move, and re-clutch. The encoders update scope.exe (the scope control software) on the position of the mount, and I am off and running again.
I also have discovered the fun of using the LX-200 interface that Mel Bartel's scope.exe software supports. You can use a planetarium program (like Earth Centered Universe) or an autoguider program (like Marty Niemi's Guider.exe) to interface to the mount for showing where the scope is aimed, or using the powerful LX-200 interface to control the mount. My plan was to use the laptop that I operate my CCD camera with (Win98, running CBWinCam, the excellent acquisition software Veikko Kanto wrote for Cookbook 245 ccd cameras), and also run Dave Lane's Earth Centered Universe, on the same machine. Then I could just do an Alt-tab to move between the two programs to move to a target, and then take an image of it....
The Problem......(and solution!)
However, the problem is the older laptops I use only have one serial port, and encoders, and LX-200 interfaces are all serial. I needed to add a second serial port to the machine running scope.exe (in a DOS 6.22 environment). The laptop also did not have a PCMCIA slot to add a serial port that way (and unfortunately even my "newer" laptop will not support doing that even thru its PCMCIA slot, since its BIOS does not support the busport protocol required to add a port via PCMCIA).
Both laptops DID have unused modems however!!!! So I asked around to see if anyone had ever connected two laptops via modems, but NOT over the telephone lines.... Lots of folks responded, with a lot of good suggestions, but none seemed to work for me. Then Ben Davies rose to the occasion, and he and his friend Joshua Titus developed a circuit to emulate a dial tone and the modem to modem link was solved (almost). The problem was to get the Windows machine to open the comm port and configure the modem, and then relinquish the comm port to the planetarium program. Dave Lane (Earth Centered Universe) wrote a small program called "Modem.exe" that solved THAT problem...... Then Ben came up with the idea to use "echo" commands on the DOS machine to configure the modem without a terminal program, and we were in business!!!!
The layout:
The configuration I normally use is with 3 laptops. Laptop#1 (a Compaq LTE/Lite 25mhz 486, DOS6.22) runs scope.exe and actually runs the telescope mount. Laptop#2 (a Compaq 5100 90mhz P1, W98se) runs the planetarium program (Earth Centered Universe, by Dave Lane) and also runs my ccd camera acquisition program (CBWinCam, by Veikko Kanto) for my CB245 camera. Laptop#3 (a ZEOS subnotebook, 25mhz 486, DOS6.22) runs the autoguider software (Guider.exe by Marty Niemi) and interfaces with my Greyscale Quickcam.
Click here for a .gif file showing the "Nominal" configuration I now setup...
If you do not use encoders, and do not want to build a UART interface to emulate a 2nd handpaddle, and your autoguider interface supports LX-200 protocol (like Marty's does), you can use a layout like this (click here)
The two keys to getting this approach to work are Ben and Joshua's Carrier Emulator Circuit (see it on Ben's webpage at: http://ben.davies.net/computers.htm ) and the Modem configuration program written by Dave Lane. Download the modem program by clicking here. Unzip the archive and you will find two programs. One is the executable (Modem.exe) and the other is the configuration file it uses (Modem.txt) to configure the modem.
The setup and use:
The exact setup and use will probably vary between systems, since each laptop seems to have its own unique requirements. For instance, my Compaq LTE/Lite allows me to specify that the internal modem is assigned to comm2 from the bios setup. Ben's IBM Thinkpad requires a slightly different approach that he outlines on his webpage.(Click here for his setup).
Initial setup:
I listed a step by step approach below for how I initially set up my
system. It is entirely based on Ben's approach he developed, but due to
laptop differences I lucked out and am able to use a slightly simpler
approach... It looks more complicated than it really is. The *
steps are only required for the initial startup. (DOS:
refers to an action on the DOS6.22 machine, and W98: refers to an
action on the W98 machine):
*DOS: Ensure BIOS setting enabled the internal Modem to
Com2, and the external serial port to com1, Update config.dat
to have LX-200 commands ON listening to Comm2
DOS: Connect modem to carrier emulation box, and then Boot to DOS Prompt.
W98: Insert PCMCIA modem card, connect telephone RJ-11
connector to carrier emulation box, and Boot to W98
---- : Power on the Carrier Emulation Circuit
W98: Run modem.exe (verify there are no errors
associated with "no carrier, but ignore the other error messages)
DOS: at the DOS prompt, type: echo ata>com2
(The modem on the DOS machine will answer the modem on the W98 machine.)
DOS: When the handshake tones go silent, then start
scope.exe on the DOS machine with a c:\scope
*DOS: ensure LX200 commands are enabled on the main menu
screen for scope.exe
W98: Close the window that modem.exe had opened.
Start your planetarium program (Earth Centered Universe, etc.) Configure it to
use Comm2 with no flow control. Then enable the telescope
interface from within the planetarium program (ECU uses Control/Alt/T).
Using the system:
W98 or DOS: Sync the scope and Planetarium program
together (from W98 in ECU, click on a target that the mount is tracking, then
click sync. Or, from scope.exe, call up datafile for target scope is aimed
at, and hit "R").
W98: Enable planetarium program to track scope (in ECU, hit
a "T" and cursor will show where telescope is aimed and change display
when cursor moves off screen to keep it visible). Command
scope.exe to move to a new target (In ECU, click on new target and then click on
"scope" in dialog box. LX200 commands will be issued to DOS machine
running scope.exe and the mount
will move to the new target, with the cursor following along during the slew)
DOS: You can also command the mount to move to a new target
from within scope.exe by calling up datafile with target, and then hitting a
"1" to move to input Eq. coordinates that were called up.
On the W98 machine, the cursor will show where the scope is aimed during the
slew....
I am forever in debt to Ben Davies and his buddy Joshua Titus, as well as to Dave Lane for their expertise in solving the tough technical challenges of getting this approach setup and functional and their spirit of sharing in making their efforts available to everyone. The ability to integrate ideas from Nova Scotia, California, and Texas really points out the power of the internet!!!!
Chuck
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