Andy's Astro blog: April 2012

So one of my projects over the weekend was to extend the cord on my NexStar 8SE's hand controller. It uses a 6pin conductor, so I had to run to radio shack for the right parts (25' cord part # 279-422 and 6c inline coupler part # 279-007, 21.14 total price after tax). It worked wonderfully, eliminating the "snapback" problem of the short, coiled cord that comes with the scope. Feeling adventurous, I decided to tackle computer control. I installed the nexremote software that came with my scope (version 1.6.14) and plugged in my generic usb/serial adapter. To my surprise, the software found my scope and it worked beautifully. Next I decided that I wanted to use a third party starmap program, Stellarium, to control the scope. The idea being that initial alignment of the scope would be handled with the nexremote program, then I could open Stellarium and use "point and click" slewing. This is where it all fell apart.

Since two programs cannot connect to the scope via the same com port, a virtual com port must be started in nexremote to allow programs such as Stellarium a connection to control the scope through nexremote. When I attempted to open a virtual com port, I always received the error message "Cannot open virtual com port #". I downloaded and installed the latest version of nexremote which fixed the virtual com port problem. I activated the scope control plug-in in Stellarium and chose the correct virtual com port for control. I was off to the races, or so I thought. Every time I selected an object in Stellarium, I got the "slew limit" error on the nexremote and the scope would not move. Turns out the firmware in my scope's hand controller, which handles communication between nexremote and the scope itself, is 4.20. Firmware 4.20 has a well known bug which causes communication errors in programs like Stellarium.

At this point, I knew I had to update my hand controller's firmware, either reverting back to stable 4.18 or try the beta 4.21 which is supposed to fix the problem. I downloaded Celestron's HC update program and connected the scope again to my laptop. I set the HC in programming mode until "Transmit Data" showed on the screen (indicating that the hand controller is in programming mode". I selected the correct com port in the HCupdate screen and attempted to connect. No matter what I try, I never get past the "Hand controller not in programming mode" error, despite the hand controller screen clearly showing that it is in programming mode.

I did a little research on the cheap-as-hell serial-to-usb adapter that I got in ebay. Turns out, it doesn't even use the real Prolific PL-2303 chipset, but rather a counterfeit chinese chipset known to cause errors. Boy does it ever cause errors. I tried the Prolific driver that is working on my laptop on 4 other computers without success. I even tried installing other generations of the driver without luck. Inevitably I always get a problem icon in device manager indicating that the device failed to start (error 10). This is common for these counterfeit chipsets, and honestly I do not know by what miracle it is even working on my primary laptop.

So it boils down to the fact that I have a half-assed semi-working adapter that I cannot make work in any capacity on any other system. I cannot update the firmware on my telescope's hand controller without either purchasing a new adapter, or finding someone with an internet connected computer with a real serial port on it. Then I have to haul my mount and hand controller to that computer to complete the update, which should give me Stellarium control via my primary laptop.

Bottom line is that these archaic serial ports have gone the way of the dinosaur. It is a mystery to me why Celestron and other manufacturers still insist on cobbling their products by using interfaces that offer sketchy performance with adapters. I challenge you to find one laptop manufactured in the last 5 years with a native serial port. Get with the program, Celestron, and use USB connectivity.