Wireless Telescope to Computer Interface – A Bluetooth Based Solution by Monroe Pattillo President, South Florida Amateur Astronomers Association (www.sfaaa.com)
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 Bluetooth as a technology solution other forms of RS-232 asynchronous serial to wireless interfaces, both proprietary and Wi-Fi, 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 Bluetooth and Wi-Fi RS-232 to asynchronous serial to wireless interfaces were evaluated.This article covers Bluetooth.A follow up article will cover Wi-Fi.
Bluetooth has several advantages over Wi-Fi.Bluetooth was initially designed as a wireless technology replacement for short length cables.Via its SPP (Serial Port Profile) Bluetooth supports transparent replacement of RS-232 asynchronous serial cables.The computer to telescope interface cable is one such cable.Bluetooth implementations are meant to be inexpensive, physically small, and not consume a lot of power.Think Bluetooth headset for a mobile phone.They’re small, they’re not that expensive, and models exist with a long lasting battery.
There are downsides to Bluetooth versus Wi-Fi.Bluetooth is meant for short range, lower speed (700Kbps or less) communications.In the real world, it’s typically around 30 feet, and it tops out at a little less than 700Kbps.There are Bluetooth version 2.0 withEDR (Enhanced Data Rate) products with a somewhat longer theoretical range of 60 feet and a theoretical top speed of over 2Mbps.Since Bluetooth 2.0 with EDR is somewhat newer, we’ll focus on the more readily available non-EDR version of Bluetooth.The newer version is backward compatible with the older version.The Bluetooth device used in this solution is version 1.1 and the computer uses a 2.0 with EDR interface.
Bluetooth is not meant to operate in a large network with lots of transmitters, which may be of concern for large star parties if the density of telescopes using Bluetooth within a 50 foot circle is in excess of twenty, not very likely under most circumstances.Bluetooth is also typically not routed across larger networks, such as the Internet.Using TCP/IP protocols on top of Wi-Fi affords a better solution for Internet remote control of telescopes.That’s not to say that it is impossible to use Bluetooth, it’s just a bit more complex to do it with Bluetooth because you need a Bluetooth to TCP to IP router to adapt the Bluetooth protocol to something that is Internet routable.
Selecting the Bluetooth Adapter
The Internet accessible documentation for a few brands of Bluetooth 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 it, 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.
After evaluating the available documentation, the range of Bluetooth serial to wireless adapters fell into two classes, interface powered and externally powered.Telescopes have very simple RS-232 interfaces.They are typically classical three wire interfaces, transmit, receive, and ground.As there are no hardware interface signals (RTS, DTR, or RING) from which the Bluetooth interface can be assured to draw its power, so I ruled out product lines and product models that could only be powered by the hardware interface signals.Bluetooth products that could be powered either by the interface or by an external power source were still in the running so long as the interface power source pins could be left out of the connector or cabling adapter.I was also looking for something that had a minimal package size, as well as a minimal price.
The product I chose was the BC-02 by BlueConsole in Orlando, Florida (www.blueconsole.com).They typically supply Bluetooth serial to wireless adapters that directly plug into the console interface of CISCO networking equipment.The device is a little larger than a 9 volt rectangular battery and has a captive RJ-45 plug tail cable which is meant to be plugged into the console port of the CISCO equipment.The BC-02 can be powered by the hardware handshake signals of the RS-232 interface via its RJ-45 plug or it can be powered by a 9 volt rectangular battery plugged directly into the 9 volt battery connector mounted on the back end of the BC-02.Just remember that if you are adapting this Bluetooth solution to other RS-232 interfaces that the BlueConsole BC-02 does not support hardware flow control.So long as your telescope supports a classical three wire RS-232 interface (transmit, receive, and ground) the BC-02 should suffice.
Acquiring the BC-02 from BlueConsole couldn’t have been easier.I ordered the product online, let them ship it USPS ground, paid via PayPal relay of my credit card, and received e-mail order confirmation and shipment tracking updates from USPS.It arrived in five business days.
The product shipping materials are minimalist. It arrived in a brown 7”x9” bubble envelope.Inside the envelope there was a packing slip and the BC-02 inside a zip top plastic bag not much larger than the BC-02.In the plastic bag with the BC-02 was a note indicating I should go to the BlueConsole web site for documentation, firmware updates, and FAQs.A bit slim, but since all the required software was already inside the BC-02 and the computer side software comes with the Bluetooth interface at the computer end, it was really all that was needed.Also, since they don’t need to ship a CD with the BC-02 there is no stale CD contents issue that is typically the case with device drivers.If newer software was needed for the BC-02 it can be downloaded from their web site and uploaded to the BC-02.
The BC-02 has worked well for me.The documentation, which was fully available prior to purchase, has provided all the required information.The product has also performed well.For the initial validation testing I did not need to contact anyone at BlueConsole.It was great.No e-mail.No phone calls.No snail mail.The end result is no waiting to complete the implementation of the solution and no waiting for problems to be resolved before proceeding to use the solution.
After the initial validation I did exchange a few e-mails with them to get updated firmware to support multipoint connections and to confirm the operating voltage range of the device.Multipoint functionality is atypical for commodity Bluetooth devices.This allows both my PDA and my PC to simultaneously interface with the telescope.This is also convenient should the focusing or tracking application be on a different system than the planisphere telescope pointing software.Confirmation of the operating voltage range information was needed to determine if the BC-02 could be powered by a source other than a 9V battery, such as by splitting the 12V to 18V DC power of the telescope.My contact at BlueConsole was quite responsive, providing firmware, an application note, and wanting my feedback.Maybe they’ll find they have a new market for their product – astronomers.
So far, so good, but I need to come up with a way of getting from the CISCO console specific wiring pinout of the RJ-45 plug on the BC-02 to the RJ-14 jack on the LX-200 telescope.
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, however the signals were not crossed in the connector as the cable plugs directly into the telescope.
I now had a Bluetooth 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 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 BC-02 and battery out of the way of telescope fork arm movement above the interface panel or the BC-02 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.
One BlueConsole BC-02 – www.blueconsole.com – $129.00 list – Internet order, direct from manufacturer – USPS ground shipping of $6.00 and Florida Sales tax of $7.74 were additional
One 9 volt rectangular battery – used easily acquired alkaline battery
One 8 wire RJ-45 female to RJ-45 female straight-thru modular coupler – RadioShackpart number 279-444 $7.99 list (already had one 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)
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
Tiny scissors or a small utility knife – to work the sheath on the telephone cord
The only tool work that is required is replacement of one of the RJ-11 plugs on the telephone cord.Everything else just plugs together as easily as typical RJ type plugs, jacks, and couplers.
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 Yellow, Black, no connection, and Red.Use the scissors to clip the Green wire off back into the sheath of the cable with no connection on the RJ-11 plug.This is done to avoid connecting a ground signal from the BC-02 to the Miscellaneous interface transmit wire of the telescope.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 the unmodified end of the telephone cord into one end of the RJ-45 modular coupler.Plug the BC-02 into the other end of the RJ-45 coupler.When you’re ready to use the interface plug a 9 volt rectangular battery onto the 9 volt battery connector on the end of the BC-02, making sure you correctly mate the DC voltage polarity of the battery to the BC-02 to avoid shorting it out by attempting to connect the battery backwards.To increase the longevity of the battery disconnect the battery from the BC-02 when not in use.
A readily available alkaline battery was used only because I couldn’t locate a Lithium battery in the store I happen to be in when the thought occurred to me that I’ll need a battery for the BC-02.An evaluation of battery longevity in telescope applications has not been performed.I’m still working with the first alkaline battery so battery life is not currently an issue.If it becomes an issue, a Lithium 9 volt rectangular battery should solve the issue.Packing a spare battery with your equipment also makes sense.If battery life becomes a serious issue, a power adapter (DC or AC to DC) could be used.As a fallback include the original wired cable in case anything goes awry with the wireless approach, not that it will, but it’s best to be prepared.
Telescope ChangesThere are no modifications, changes or software additions needed on the telescope side of the connection.The BC-02 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 Bluetooth interface converts the serial data to and from Bluetooth 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.
To keep the BC-02, cable, and battery neat to the telescope a small square of Velcro was attached to the telescope and to the back side of the BC-02.A small zip tie was used to dress the excess cable length into a small loop.This keeps everything out of the way of the telescope fork arms and avoids dangling the BC-02 and battery by the connecting cable.
To keep all the parts of the solution together I keep the BC-02, with disconnected battery, the RJ-45 coupler, and the modified telephone cord in a zip top sandwich bag in my equipment bag.
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.
Just to get the Bluetooth impacting Wi-Fi issue out of the way I’m also investigating a Wi-Fi based RS-232 asynchronous serial to wireless solution for telescopes.This is to avoid the potential for wireless implementation technology battles at star parties.I haven’t yet heard of astronomers banning Bluetooth enabled mobile phones and PDAs from star parties due to Wi-Fi performance impact, but I like to have solutions before problems take root.
Computer Side of the Solution
The computer will need a Bluetooth interface to communicate with the BC-02.Some computers come with a Bluetooth interface built-in to the computer.For other computers you will need to acquire a Bluetooth interface.They come in a number of interface solutions, including USB and PCMCIA or CardBus.Whatever your approach to getting a Bluetooth interface on your computer, just make sure it supports at least Bluetooth version 1.1 or 2.0 and that it supports client connections to SPP (Serial Port Profile) server devices so as to provide virtual COM port emulation to connect to the Bluetooth SPP server inside the BC-02.
Once your Bluetooth interface has been installed on your computer, configure a connection profile to connect the virtual COM port emulation of the Bluetooth interface in your PC to the SPP server in the BlueConsole device.This usually involves telling Bluetooth on your PC to discover available services on other devices and computers.You should discover the SPP server interface within your BC-02.If it doesn’t appear, resolve that problem first.
If your computer requires a secure Bluetooth connection the PIN code of the BC-02 defaults to 1234.This can be set to a different value on the BC-02.The documentation available on the BlueConsole web site will walk you through this change.I recommend leaving it at the default unless you are required to change it.Bluetooth devices have a manufacturer provided worldwide unique hardware address, similar to the MAC addresses of Ethernet devices.This ensures the uniqueness of the Bluetooth device connection.You do not need to change the Bluetooth connection PIN to make it unique.The PIN is for security, not device identification.
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
BlueConsole BC-02, software version 3.5 and 3.7 for multipoint connections
Bluetooth 2.0 EDR interface (manufactured by Cambridge Silicon Radio) inside of a Toshiba Qosmio G35-AV650 laptop computer.The Toshiba Bluetooth software stack version is 4.00.25.(T).
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 Bluetooth interfaces should be possible so long as the Bluetooth interface supports at least version 1.1 and virtual COM port emulation for connection to SPP (Serial Port Profile) devices.
To make use of your Bluetooth wireless PC to telescope interface go through the following steps, in the following order.
- Connect the RJ-45 coupler to the BC-02
- Connect the modified telephone cord between the telescope and the coupler
- Connect the battery to BC-02
- Turn on the Bluetooth interface on your PC
- Tell the Bluetooth software on your PC to connect to the BC-02
- Launch your telescope control software
- Tell it to connect to the port associated with your Bluetooth 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.The first time I connected to my BC-02, I was on COM40.A Bluetooth configuration adjustment was made soon after to my PC.
Make sure you turn off any hardware (modem) signal flow control on the Bluetooth virtual COM port, or telescope application software.
If for some reason your Bluetooth 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 Bluetooth to BC-02 connection on your PC, and restart your telescope control software.
Going Truly Mobile
I own a Windows Mobile based Hewlett-Packard iPAQ 2215 PDA.It has a built-in Bluetooth interface.This Bluetooth solution has been validated using Software Bisque’s TheSky Pocket Edition (version 1.10.014) controlling the LX-200 telescope – wirelessly.Owners of Bluetooth enabled Palm OS based PDAs take note, TheSky Pocket Edition runs on Windows based PDAs.
A PDA controlling a telescope via Bluetooth, that sounds a lot like a telescope wireless hand paddle – with built-in planetarium software.Telescope setup is still performed with the wired hand paddle of the telescope.Once set up, my laptop, or my PDA, can control the telescope.
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.I’ve seen an advertisement for a product that uses Bluetooth technology and is only about $20 more expensive than the BC-02.This product knows its purpose in life is telescope control, its packaging is somewhat larger, and you don’t have to make a cable, but it didn’t indicate that it supported multipoint connections.I was looking for something that was generic Bluetooth on both ends and didn’t know that it was working with a telescope let alone a particular brand or model of telescope, and I liked the plus of Bluetooth multipoint support, 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 Bluetooth version 1.1 or later interface on your computer that supports SPP.The BC-02 shouldn’t be able to tell the difference.
Software Bisque – TheSky Pocket Edition
912 12th Street
Sales Phone 800-843-7599
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)
Fox Observatory is open to the public Saturday evenings until at least midnight