Sky Commander changes that worked for me
The Sky Commander is no longer made.
This info may help if you happen to own one.
The Nexus Pro and the Argo Navis have the same encoder pin-out and RJ45 plug that the Sky Commander used for an easy replacement. The serial port wiring is different between all three.
First, I need to say that Sky Engineering made a great Digital Setting Circle (DSC) product called Sky Commander.; I liked enough that I have two - one for my Losmandy German Equatorial Mount (GEM) and another for my Dob mounts. The Losmandy version was bought from Losmandy with their encoder mounting kit. When I built the Dobs I decided to also get the Dob mounting kit ($40 at the time without encoders) from Sky Engineering. After 15+ years using the Sky Commander on the GEM and over ten years with the Dob setup I have found a few areas that could be improved, at least for me.
A Wireless PC to Sky Commander Connection
I liked the connection between the DSC and a notebook PC, but the cable was a pain, especially with the DOB, since the Sky Commander rotated with the Alt axis. This is, of course, not a design fault, just something that annoys me.
I looked into quite a few options for this. WiFi, 900Mhz, and Bluetooth were the leaders. Bluetooth won, mainly because of the low price and power needs. There is little known Bluetooth profile called SPP, or Serial Port Profile. This allows PC software, such as The Sky, to talk to the Bluetooth hardware using a serial port. The problem was that my 6 year old (and used then) notebook didn't have Bluetooth and the Sky Commander wasn't likely to sprout one in the near future either. At least it wouldn't without some help.
Since the PC did have a USB 1.1 port I went for a USB to Bluetooth dongle. Specifically the D-Link DTB-120, which sells for about $20 from Amazon. I've also used models by Linksys, AmbiCom and those built into newer notebook PCs - they all work. The Sky Commander, which only has a serial port was a little more difficult. For that I decided on a BrainBoxes BL-819 serial to Bluetooth converter from TekGear for about $85 (I was told that the price has gone up quite a bit since then). This great little device does all of the work and the serial device that it's connected to thinks that it's shoving bits through a wire. The set-up looks like this:
I wanted to see if there was a less expensive serial to Bluetooth option. I have been using a CableMax RS-232 to Bluetooth adapter and it has worked well and cost about $50. The only bump was that the Cablemax and the Brainbox swap the serial transmit and receive wires. This can be fixed with a Null serial adapter or you can create a new cable. Below is the serial cable that I made.
The wiring to make the DCE cable.
The CableMax RS232 to Bluetooth adapter with a cable to attach it to the Sky Commander.
The BL-819 does need an external power supply. It comes with a wall plug adapter, which is great for testing and setup, but not practical for the rotating Dob in the field (but okay for a GEM mount). I put together a 4 AA cell NiMh pack that should power the BL-819 for an evening before recharging. If not I'll swap batteries. The BL-819 takes a 'B' power tip (4.0mm O.D., 1.7mm I.D.) from Radio Shack, if you should to build your own power pack.
For the Maxx Telescope I made a 12v to 5v regulated power converter using a 7805 IC and three capacitors. It also passes through 12v for the Sky Commander. I needed something light weight since it would be mounted on the secondary cage.
I also made a one foot serial cable to connect it to the Sky Commander. Only pins 2, 3 and 5 are needed on the DB9. The plan is to have all of the parts except the encoders ride on the tube rings of Griffin
I've tested this set-up on with The Sky V5 and V6 at 9600 baud, 8, N, 1 with no flow control and level 2 security on the BL-189. I expect that it would work well with any software that talks to the scope via the serial port.
Newer PCs often have Bluetooth built-in so the DBT-120 wouldn't be needed. If you have a really old PC that doesn't have a USB port you could get the BrainBoxes BL-830 to connect to the PC's serial port, a USB PCMCIA card and a DBT-120, or is such a thing exists, a PCMCIA Bluetooth card.
The DBT-120 has an official peer-to-peer range of 30 Feet and the BL-819 claims a 30 Meter range.
The wireless connection has been tested now to about 40' while going through two concrete walls. Since this is further than I usually have the scope from the computer and there should be considerable fewer electronic gizmos around I expect the range to be good enough. If not, there are other USB/Bluetooth devices with a greater range. There are a few Bluetooth adapters that have a flip-up antenna and tout a 150 Meter range.
I also tried out an AmbiCom USB/Bluetooth adapter. Both it and the D-Link use the same WIDCOMM Bluetooth software, but since they renumber it I don't know if it's the same version. The D-Link has dimmer green LEDS and the AmbiCom uses a bright blue LED. The Blue LED would be a problem at a dark-sky star party.
Reading the Sky Commander RA and Dec via a PIC
This was an interesting exercise. Originally I was going to use this to control a go-to Dob mount. It's unlikely now that Sky Engineering is not selling the Sky Commander any longer. Note the red on black LCD display. I would have liked the Sky Commander to have switched to that instead of the black on green.
I found that the data from the Sky Commander came over in the native HC11 binary floating point bias format. This was close, but not a match to the binary floating point format of the PIC. So it took some rearranging of the bits within the four bytes of the floating point value to make the PIC happy. In the end I was able to read the data and found that the Sky Commander actually output the values to two decimal points, even though the Sky Commander only displayed one decimal point.
In the example above the Sky Commander displays 321.0 and 47.0 where the PIC displays (with the red display that the Sky Commander should have had) -38.98 and 47.03. While the first numbers don't appear to match the -38.98 any value less than zero should be subtracted from 360 degrees to make it positive, so 360 - 38.98 = 321.02, which, when truncated to one decimal point, matches the Sky Commander.
Below is some info about the difference between the floating point data to feed your inner nerd.
Inside the Sky Commander
Here's the inside of the Sky Commander XP4. The left side controls the display and buttons and the right side houses the power, serial and encoder interfaces and the CPU. It's powered by a Motorola MC68HC11F1CFN3 CPU (12MHz Max). The socketed memory chip is a M27C1001-12C1 with 128K of flash ROM.
At the top of the right side in the silver casing (ECS H 7.37-S) is a 7.37 MHz Ceramic Resonator, the clock that controls the CPU speed. The dark chip to its right, a Maxim MAX231CWE, converts 5v 'chip' power signals to 12v signals used by the serial port and back. At the bottom is a LM317T, which is an adjustable voltage regulator likely used to drop the incoming 9-12v power to 5v for the system to operate.
Slipping Pivot Bolt Fix
On the Dobsonian The pivot bolt slipped against the ground board, not just on my scope, but on three others as well (all built by different people). The symptom is that you move the scope but the Alt encoder numbers don't change, or seem to slip.
I ran into this the first night out. The temporary field fix was to drill a small hole in the large fender washer on the underside of the ground board and epoxy the pivot bolt to the fender washer and smaller washer (see photo below). This worked, for about two nights. A more permanent fix was needed. It was found in the form of a Torque Washer. A Torque washer is, in this case a stainless steel washer with a square center hole and spikes that dig into the wood to prevent it from twisting. The square hole fits the square part of a carriage bolt. The 3/8" x 1-1/2"x carriage bolt screws into the machined Sky Engineering machined part that goes into the telescope's base board replacing the 3/8" bolt that came with the kit. I intentionally said that the Sky Eng part screws into the bolt because the bolt can no longer turn. It is IMPORTANT that you use some thread lock when you screw the Sky Engineering part onto the new bolt or the threads will turn and you will be back to where you were. Stainless torque washers are a somewhat unusual item and the only place that I've found them is McFeeley's
The original part with the field fix on it. It worked long enough (with additional epoxy) to get me through the star party.
The Torque washer with the hole for the old lock screw next to it. Since this is the bottom of the scope no one will see it, but it still looks better. You can see the hole from the previous attempt with the washer and wood screw.
The final version used a stainless carriage bolt welded to a stainless torque washer to prevent any motion. Otherwise if the bolt backs out, even a little, it will move side to side and throw the encoder off. This has worked for many years.
Other solutions that were discussed were a jam nut on the top of the ground board and one-piece Delrin bolt/washer combo with a lock screw hole in the oversized head.
Coiled cable between Sky Commander and Encoders on a GEM
The cables that came with the 2003 Losmandy were the long straight type used for Dobs so there was quite a bit of coiled up cables lying around. This was not a design problem, especially since the cables were from a Dob kit and resold by Losmandy, just something that I didn't care for.
The GEM cables were shortened by taking a 25' black coiled phone 4-wire handset cable and cutting it into two parts. One end of each cable has a RJ-11 end and the other end of each come together into a RJ-45 end. The end that connects to the RA encoder can be pretty short (on the Losmandy G11 anyway). The seam on the wire goes into the RJ-11 the same side on both, but it alternates on the RJ-45 end. Look at your existing cable when you make this and it will make sense.
