Wireless Telescope to Computer Interface – A Wi-Fi Based Solution by Monroe Pattillo
President, South Florida Amateur Astronomers Association (www.sfaaa.com)
This is the second of two articles on wireless telescope to computer interfaces.The previous article focused on Bluetooth.This article focuses on a Wi-Fi based solution.
As in the previous article the goal was to replace the RS-232 computer to telescope interface cable with a wireless interface.The justification was to eliminate a cable trip hazard in the dark and to reduce, at least by one, the number of cables connecting the computer to the telescope (still currently need a cable to connect the camera mounted on the telescope to the computer, but I’ll get to that one eventually).By eliminating the telescope to computer interface cable set up and teardown times are also reduced since you don’t have to take the time to use a long cable so that you can route it carefully down to and along the ground to avoid the creation of a waist height trip in the dark hazard.
This solution is for the RS-232 asynchronous serial interface of the telescope.It is not meant for, nor has it been tested to, replace the cable to the telescope hand paddle (which may also be RS-232).The hand paddle has lights on the buttons and a display which are significant power consumers.A telescope hand paddle is provided its operational power via the interface cable.This makes a hand paddle solution more complicated.The signals can be converted from wired to wireless easily enough, but you still need a cable, or lots of batteries to power the hand paddle.Telescope hand paddle wireless solutions are for future study.
While this article focuses on Wi-Fi as a technology solution other forms of RS-232 asynchronous serial to wireless interfaces, both proprietary and Bluetooth, were also investigated.I have a personal disagreement with all things proprietary.Particularly when standards based (even de-facto, so long as they are commodity product) solutions, such as Bluetooth and Wi-Fi, are readily available and offer brand independent interoperability.The cost to build proprietary solutions may be less for the manufacturer, but the consumer price for proprietary products is typically higher and the products less flexible.The window of production availability of standards based solutions is also typically longer than that of proprietary solutions.This longer window of availability is particularly useful if you ever need replacement parts or have a friend who wishes to deploy the same solution.
Both Wi-Fi and Bluetooth RS-232 to asynchronous serial to wireless interfaces were evaluated.This article covers Wi-Fi.A previous article will covered Bluetooth.
Wi-Fi has several advantages over Bluetooth.The underlying TCP/IP protocols Wi-Fi uses for remote access to asynchronous serial ports have been around years longer than Bluetooth.Solutions for remote access to serial ports based upon Ethernet LANs have been around for some time.Substituting a Wi-Fi wireless interface for the wired Ethernet LAN interface is somewhat new.TCP/IP based Wi-Fi implementations are meant for higher performance solutions than Bluetooth, think tens of megabits for TCP/IP versus hundreds of kilobits for Bluetooth.TCP/IP is also meant be routable across large IP networks and even the Internet, thus addressing in TCP/IP is meant for large populations of directly addressable end devices.Bluetooth is meant for local personal area networking.TCP/IP based Wi-Fi is meant for access across the Internet.Using TCP/IP protocols on top of Wi-Fi affords a better solution for Internet remote control of telescopes.Wi-Fi is also meant to cover large physical areas and often allow for antenna substitution for even larger area coverage.
There are downsides to Wi-Fi versus Bluetooth.TCP/IP based serial adapters, such as the one used in this Wi-Fi solution, are typically more expensive than their Bluetooth counterparts.This is because they are assumed to be used in commercial or industry applications like data centers and communications switching centers and not expected to be sold directly to consumers for end use applications.As a result, the devices are expected by their market to be built more physically rugged, with special built enclosures, connectors for flexibility, and molded cables with industry recognized connector pinouts.The lower product use volume of their market also keeps the price somewhat higher than their Bluetooth equivalents.
Selecting the Wi-Fi Adapter
The marketing name “Wi-Fi” encompasses a collection of IEEE 802.11 wireless protocols (b, a, and g) offer various levels of performance, covering multiple radio frequencies, and products include proprietary mechanisms for increasing the performance.The 52Mbps 802.11g protocol is commonplace in commodity products these days.This article focuses on the most prevalent Wi-Fi protocol, the 11Mbps IEEE 802.11b, which is backward compatible with 802.11g, and avoids proprietary performance improvement protocols.
The Internet accessible documentation for a few brands of Wi-Fi based RS-232 asynchronous serial to wireless adapters were examined.If there was no Internet freely accessible documentation, or it lacked sufficient technical details, or it required a password to access product information, I skipped the product.Much as with proprietary solutions, I avoid solutions for which the technical details of the product are left a mystery until after you purchase the product or make contact with a seller.The worse case solution implementation and validation scenario is to have to call someone in product technical support on the phone, only during normal business hours, for their time zone, and wait in the phone queue, to obtain trivial information such as the wiring pinout of a connector on their product or the commands necessary to initialize or configure their product.
Telescopes have very simple RS-232 interfaces.They are typically classical three wire interfaces, transmit, receive, and ground.There are no hardware interface signals (RTS, DTR, or RING) from which a self-powered interface can be assured to draw its power.I ruled out product lines and product models that could only be powered by the hardware interface signals.I was also looking for something that had a minimal package size, as well as a minimal price.
I was also looking for a TCP/IP to serial adapter that supported a transparent tunnel mode of operation, e.g. characters received at either end are passed to the other end without requiring the data to be enclosed in any sort of protocol by the initiating application.This is great for validation purposes as I can connect a COM port on my PC to the adapter and then establish a TELNET session via Hyperterminal on my PC.I don’t want to be left wondering why StarryNight isn’t controlling my telescope when the problem is with the TCP/IP stack or the virtual COM port software.
It is common for TCP/IP based devices to have a built-in web server for configuration and status management.I also wanted this in the device I selected to avoid requiring the installation of proprietary configuration and status management software applications on my PC.
The product I chose was the AirborneDirect ABSE-100D by Quatech in Hudson, Ohio (www.quatech.com).They supply serial to wireless adapters for a number of commercial application markets, including industrial and medical.The device is about the size of two decks of cards stacked one atop the other.It is powered by an external AC-DC power adapter.The power source is connected to the device via a common 2.1mm barrel jack.For field use it should be easy to locate a 12V DC cigarette lighter plug to 5 V DC barrel plug power adapter for use in the field (if you don’t have a 12V DC battery and 110V AC inverter).
The ABSE-100D includes a captive serial cable terminated by a molded 9 pin D type male connector.This is the connector type and pinout typically found on a PC.The connector supports transmit, receive, and ground, as well as two handshake signals (RTS and CTS) which are not used in this solution as they are not required by the telescope.So long as your telescope supports a classical three wire RS-232 interface (transmit, receive, and ground) the ABSE-100D should suffice.
The device supports optional use of an encapsulated protocol for TCP/IP to serial communications as well as a transparent tunnel mode.I chose to use the transparent mode of operation.
The ABSE-100D also included a pair of software applications for establishing virtual COM ports to the serial device.These came free with the device, but I chose to use a similar port redirector application downloaded from the Lantronix web site.
While I could have acquired the ABSE-100D from Quatech, I chose to save a noticeable amount of money (about $60) by acquiring it from a mail order discounter (Provantage).I ordered the product online and had them ship it UPS ground (I’m patient, and cheap).It arrived in four business days.
The product shipping materials were volume production commercial grade.All the parts, software and documentation CD, and quick start and regulatory documentation came in a well labeled fold over cardboard box.The box labeling included company name, product model, serial number, firmware version, and Ethernet MAC address.That box was then packaged by the discounter into a larger cardboard box filled with packing material.
While the ABSE-100D device has worked well for me, the virtual COM port software was replaced by me with the equivalent software from Lantronix.I didn’t like the DPAC VCOM software provided with the ABSE-100D as it required too many system restarts and it caused hangs, and one crash.There was no newer version of the software on their web site.I had no desire to take time assisting them debug their application, so I replaced it.If the device had performed at this level I would have replaced it with a product from a different manufacturer.
I needed to come up with a way of getting from the DB-9 connector on ABSE-100D to the RJ-14 jack on the LX-200 telescope.I used a common modular RJ-45 to DB-9 female adapter to get from the DB-9 to a standard modular connector.I wired three pins in the adapter, transmit (pin 2, color red), receive (pin 3, color black), and ground (pin 5, color yellow).I also created a two pin jumper and connected the Request To Send signal (RTS, pin 7) to Clear To Send (CTS, pin 8).I’m not sure if the ABSE-100D needed this jumper, but I thought I’d stem the issue before it arose.
The computer interface of the RJ-14 (three pair or six wires) connector on the LX-200 provides a classical three wire RS-232 interface, transmit, receive, and ground.The jack includes a second serial interface and a 12V DC power source, none of which is needed for this wireless solution.Nothing will be connected to the unused pins in the RJ-14 jack.Modular RJ type connectors are a family of narrow to wide multi-conductor plugs and jacks aligned on a common central tab.The three wires of the LX-200 interface occupy three out of the four central pins of the RJ connector jack on the telescope interface panel.While the connector on the telescope is RJ-14, you can use a commonly available RJ-11 (two pair, four wires) plug in the jack to interface your computer to the telescope.I’ve used the RJ-11 plug in the RJ-14 jack approach for many years as it allows me to use a fifty foot, good quality telephone extension cord to connect my telescope to a RJ-11 to DB-9 modular adapter connected to the RS-232 serial interface of my computer (remembering to wire the DB-9 adapter for use with a cross wired cable which is how a telephone cord is wired).The same RJ-11 plug in the RJ-14 jack approach was used this time.
I now had a Wi-Fi to serial adapter, and I knew the plug I needed to create to connect to the telescope.Rather than build a complete cable from scratch I chose to modify (or maybe not, see Assembly below) a one foot RJ-11 plug to RJ-11 plug telephone cord.With a shorter cable you won’t have a convenient way of getting the device out of the way of telescope fork arm movement above the interface panel or the somewhat heavy ABSE-100D with DB-9 to RJ-45 adapter will dangle in mid-air which is not good for the wiring.With a longer cable, well, you have a long cable.The use of wireless technology was meant to get rid of a long cable.If you build the cable from scratch, or modify a longer cable, you can make the cable length to suit your needs.
To join the telephone cord to the RJ-45 plug on the BC-02 I chose to use an RJ-45 jack to RJ-45 jack straight through coupler.This avoids any modifications to the BC-02, requires modification only to the telescope end of the RJ-11 cable, and provides for a modular solution that can be easily adapted to work with the RS-232 computer interface of other telescopes.
The ABSE-100D comes with a foldable stub antenna.The antenna is connected to the ABSE-100D using a de-facto standard RP-SMA screw type antenna connector.If you need a larger wireless coverage area the antenna can be replaced with a more powerful antenna or you can use a short antenna extension cable to relocate the antenna to where a larger, more power antenna can be connected.Unfortunately, there is insufficient space between the connector and the case for installation of the larger connector nut found on inexpensive 5dBi and 7dBi antennas with RP-SMA connectors.Fortunately, under the majority of circumstances the antenna supplied with the ABSE-100D should suffice, even when the antenna is flipped down along the case.
The power connector of the ABSE-100D is a commonly available barrel jack.The cord of the AC-DC adapter dresses downward alongside the serial cable.You can likely acquire a 12V DC cigarette lighter plug to 2.1mm barrel plug power adapter.Just remember it needs to supply +5V DC at 1.5A, not 12V DC.
The serial port, network, and wireless of the ABSE-100D are configured via its built-in web server.The serial port was configured for 9600 bits per second, 8 data bits, 1 stop bit, no parity, no hardware handshake, and for transparent tunnel mode.
One Quatech ABSE-100D (includes antenna and AC-DC power adapter) – www.quatech.com – $229.00 list – Internet order from discounter (PROVANTAGE) for $168.84 – USPS ground shipping of $5.45 was additional
One 8 wire RJ-45 female to DB-9 female modular adapter – similar to 31D1-17400 CableWholesale.com $1.14 (already had similar item on hand)
One 2 pair (4 wire) stranded copper (not silver satin) telephone cord, 1 foot – RCA TP130 $2.95 list (already had one on hand)
May not be needed – One RJ-11 2 pair (4 wire) modular plug – RCA TP308 modular crimp tool includes four RJ-11 modular plugs $12.95 list (had tool and plugs on hand)
The RCA TP308 is recommended to obtain the one RJ-11 plug needed to adapt the RJ-11 to RJ-11 cable as the TP308 includes a crimp tool and four RJ-11 plugs all in one kit.If you have access to a supply of RJ-11 plugs and can borrow a modular plug crimp tool from a friend it reduces the cost of the solution a little bit.
RJ-11 modular crimp tool – comes with RJ11 plugs in RCA TP308 package or borrow one from a friend
Long nose pliers for insertion of pins in DB-9 connector part of DB-9 to RJ-45 adapter
Tiny scissors or a small utility knife – to work the sheath on the telephone cord
The only tool work that is required is assembly of the DB-9 connector pins of the DB-9 to RJ-45 adapter.If you’re building your own RJ-11 to RJ-11 cable you may need a modular crimp tool for installing the RJ-11 plugs on the telephone cord.Everything else just plugs together as easily as typical RJ type plugs, jacks, and couplers.
If you buy an off the shelf RJ-11 plug to RJ-11 plug telephone cord first verify the wiring of the cable.If it is a crossover cable with wiring as indicated below you have no changes to make to the cable.If not then you will have to change one end to change it into a crossover cable.Take the foot long RJ-11 plug to RJ-11 plug telephone cord and cut the plug off of one end.Wiring in typical RJ-11 two pair telephone cords are nearly always the same colors on the same pins for the same functions, e.g. Red/Green for the inner pair, Black/Yellow for the outer pair.Whatever the colors in your telephone cord, just match them to the pictures of my adapter cable and you should be ok.
The sheath of the telephone cord is tight against the wires in the cable which makes it difficult to cross wires in the cable.Aside from removing the typical quarter of an inch of the sheath to fit the RJ-11 plug, also carefully slice the down the side of the sheath for another half inch to provide room to swap the wires around and to be able to slide the crossed wires into the replacement RJ-11 plug.Be careful to not nick the wires in the cable when removing the piece of the sheath or when slicing down the sheath.The tiny scissors of a small utility knife is ideal for these cuts.
The wiring pinout of the RJ-11 plug is straightforward.On the end of the telephone cord on which you did not remove the RJ-11 plug, look at the end of that RJ-11 plug (the end of the plug opposite the end into which the cable is inserted).Orient the metal fingers to the top and the tab to the bottom, count the pins facing you left to right 1 to 4.The colors will typically be left to right Yellow, Green, Red, and Black.You want to put the wires in the replacement RJ-11 connector (looking at it end on, oriented the same way) on the other end of the cable as Black, Red, Green, and Yellow.Put the replacement RJ-11 plug on the cable with the wires lined up as indicated previously and use an RJ-11 compatible modular crimp tool to crimp it firmly onto the cable.Afterwards look at the end of the plug and make sure all the wires are in the correct position and that they come all the way to the end of the plug.If the wires aren’t in the correct position or they don’t come all the way to the end of the plug, cut off the plug and wire up a new plug until it is correct.
Plug one RJ-11 plug end of the telephone cord into the RJ-45 end of the DB-9 to RJ-45 modular adapter.Connect the modular adapter to the DB-9 connector of the ABSE-100D.When you’re ready to use the device, connect the RJ-11 cable to the telescope and plug in the power plug into the ABSE-100D.Lastly, plug the AC-DC adapter into an AC outlet, or AC power inverter connecter to a battery.
There are no modifications, changes or software additions needed on the telescope side of the connection.The ABSE-100D will talk to the RS-232 asynchronous serial interface of the telescope just as if it was a cable connection.The telescope should not be able to tell the difference.In reality, there will occasionally be small transmission delays as the device converts the serial data to and from Wi-Fi wireless, and occasional wireless retransmissions to recover from radio noise sources.Given that the interface on the telescope operates at only 9600 bits per second there is plenty of slop time for signal conversion and the occasional retransmission.
Keep the device and cabling neat to the telescope a small square of Velcro was attached to the telescope and to the back side of the sleeve of the ABSE-100D.Two small zip ties were used to dress the excess cable.This keeps everything out of the way of the telescope fork arms and avoids dangling the adapter by the connecting cable.I fold the antenna down to keep it out of the way of the fork arms.
To keep all the parts of the solution together I keep them in a large freezer bag, including the AC-DC adapter.
Bluetooth and Wi-Fi Cohabitation
The Wi-Fi standards accommodate the detected presence of Bluetooth radio signals.This should not be an issue for Bluetooth, however it may occasionally make Wi-Fi interfaces drop from their maximum speed to a lower speed to get out of the way of detected Bluetooth radio signals.If there is substantial sustained Bluetooth use at a star party, Wi-Fi users may complain that the use of Bluetooth prevents them from sustaining the top speed of their Wi-Fi interface.This might only be an issue if they are streaming live video images over their Wi-Fi interface (not the best way to capture quality astronomical images, but someone might attempt it).At high resolution video streaming interfaces require lots of available bandwidth and don’t perform retransmissions if packets are dropped.If the video stream slows down due to the presence of Bluetooth signals, video frames could get dropped and not be recovered.Web page updates, e-mail, and digital camera downloads might occasionally take longer, but there shouldn’t be any loss of information.
I haven’t yet heard of astronomers banning Bluetooth enabled mobile phones and PDAs from star parties due to Wi-Fi performance impact, but being based upon Wi-Fi this solution should alleviate the issue before it arises.
Computer Side of the Solution
The computer will need a Wi-Fi (IEEE 802.11b or g)interface to communicate with the ABSE-100D.Some computers come with a Wi-Fi interface built-in to the computer.For other computers you will need to acquire a Wi-Fi interface.They come in a number of interface solutions, including USB and PCMCIA or CardBus.Whatever your approach to getting a Wi-Fi interface on your computer, just make sure it supports at least 802.11b.
Once your Wi-Fi interface has been installed on your computer, configure a connection profile to connect the virtual COM port emulation of the Wi-Fi interface in your PC to the serial port IP address and port number of the ABSE-100D.
This solution has been validated in the following equipment and software environment.
RS-232 asynchronous serial computer interface of an 8” Meade LX-200 Classic SCT telescope, running software version 3.34L/p>
Quatech AirborneDirect ABSE-100D, firmware version 22.214.171.124
Wi-Fi IEEE 802.11a/b/g interface (Intel PRO/Wireless 3945ABG) inside of a Toshiba Qosmio G35-AV650 laptop computer.The Intel driver version is 10.1.0.13.
Space.com’s StarryNight Pro 4.5 interfacing to the telescope via ASCOM 2.2.
Some might prefer that a newer Meade LX-200 telescope, a different brand of telescope application software, a newer version of Starry Night, or a newer version of ASCOM were used in the validation.The goal was to validate the solution for my environment, so the validation didn’t cost more or take longer.If it works with stuff this old, it’s likely to work with newer stuff as well.Given the opportunity it will be validated it with equipment at our observatory.If they let me, and they so desire it, I’ll also validate it with the software and equipment of the other astronomers in our local group.
So long as the computer interface on the telescope is a classical three wire RS-232 asynchronous serial interface, this solution should be usable on other telescope brands or models and may only require a change to the RJ-11 adapter cable (the pinout and/or the connector).Use of this solution with other brands of Wi-Fi IEEE 802.11b compatible interfaces should be possible.
To make use of your Wi-Fi wireless PC to telescope interface go through the following steps, in the following order.
- Connect the RJ-45 to DB-9 adapter to the ABSE-100D
- Connect the telephone cord between the telescope and the DB-9 to RJ-45 adapter
- Connect the AC-DC adapter to the ABSE-100D
- Plug the AC-DC adapter into a 100V power source
- Tell the COM port redirector software on your PC to connect to the ABSE-100D
- Launch your telescope control software
- Tell it to connect to the port associated with your Wi-Fi virtual COM port
Make sure the Bluetooth software on your PC configures the telescope interface COM port as COM1, COM2, COM3, or COM4 to allow it to be used with a wider range of telescope control applications which might not support COM port numbers greater than COM4.
Make sure you turn off any hardware (modem) signal flow control on the Wi-Fi virtual COM port, or telescope application software.
If for some reason your Wi-Fi wireless connection drops long enough to time out, the virtual COM port on your PC may become non-responsive.If this happens exit your telescope control application on your PC, reconnect the Wi-Fi to ABSE-100D connection on your PC, and restart your telescope control software.
This solution works and I’ve yet to see any issue that would stop it from becoming generally usable in the astronomy community.There exists other wireless PC to telescope solutions in the market, some proprietary, some Bluetooth, none of which were Wi-Fi.I’ve seen an advertisement for a product that uses Bluetooth technology and is only about $60 more expensive than this Wi-Fi solution.This Bluetooth solution knows its purpose in life is telescope control and you don’t have to make a cable.I was looking for something that was generic Wi-Fi on both ends which didn’t know that it was working with a telescope let alone a particular brand or model of telescope, so I didn’t mind making a cable to achieve that goal.
For those of you on systems other than Windows based PCs, you just need a Wi-Fi 802.11b compatible interface on your computer and virtual COM port software that supports transparent tunneling.The ABSE-100D shouldn’t be able to tell the difference.
President, South Florida Amateur Astronomers Association, Inc. (SFAAA)
c/o Markham Park
16001 West State Road 84
Phone (Saturday evenings) 954-384-0442 (other times, leave voice mail)