Wednesday, February 08, 2012

rebuilt cable

Why hadn't Phil and I been able to command (nay, order) the Losmandy mount from our computers?

I don't like being stymied by electronics, hardware, or software. It had been in the back of my brain all day. Distracting me. Tugging. Whispering, just out of range. Or maybe that's just early tell-tales of the encroaching madness. Reading and research 'round midnight, before I passed out, had fueled thoughts. Left me with ideas. Things I wanted to try. Things to be explored. More to-dos. That my brain wouldn't let go of. I couldn't take it any more. I quit work early. And resumed my investigations via the web. I was buoyed by many reporting that it worked!

One notion was to see what the Losmandy Gemini System was receiving from my computer. Upon a more thorough reading of the documentation, I noted that one could monitor the Gemini console to see what data was being received.

Another thought was to verify the communication settings were correct. Certainly in the days, many moons ago now, where I was regularly tuning modulator-demodulators and battling PC-to-PC null-modem exchanges, I worried about these things. Did I have the rate set correctly? Did I have the data bits, stop bits, parity right? The handshaking?

And, somewhere in my user guide perusals, I now had the impression that there was a possible application I might use, a Losmandy-specific software product that would talk to the mount. If this was true, if I could find this software, if I could legally acquire this tool, perhaps it could be used to test things, using a known-good utility.

And then I stumbled across a very interesting note. The manual suggested using Hyper Terminal to issue commands and monitor responses from the mount. Cool! Here was an elegant solution employing a tool I already had. Good ole' HT! Wow.

I tested a bunch of things. Including altering the FIFO buffer settings. And was not seeing anything. Nothing was working...

It was around this time that I came upon, once again, the wiring information and photo for the Gemini-to-PC cable. Simple. Three wires. We had been careful making our little test cable. Let's check it one more time, I thought. So, off to the work bench I went. After an SMS tip from Phil as to the location of the DMM, and after fabricating a small test lead, I probed the pins... and found something strange.

Pins 2 and 3 on the DB9 female plug were reversed. I checked it again. I checked for shorts. And re-read our notes in the little notebook. Yep, backwards. We had wired the cable correctly, according to our notes. But it was not matching what was in the Gemini Level 4 manual. Didn't make sense. It just didn't make sense. We had been slow and methodical. And I saw that it wasn't a complete reversal, that is, pin 5 was right. We had not transposed pin 5 from 1. How the hell did we get the Tx and Rx lines wrong then?! Baffled, I cut the wires. Redo!

I returned to the mount. Attached the patchwork cable. Powered the mount. Verified the virtual COM address allocated to the USB converter. Fired up Hyper Terminal. Set the COM port parameters as required. And typed some of the strange Gemini commands like :P# (Toggle High Precision Pointing) and :GR# (Get Telescope RA). Crikey! Something came back! It was working!

The damned cable. We built the damned cable wrong!

Booted Stellarium. And slewed the mount to Albireo. It was a thing of beauty. At long last I could complete my notes on how to drive a 'scope from Stellarium.

I thought of James from TANDBERG. Invariably the fault is with the wiring...

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