CHEAP… Bluetooth Wireless Interface for Meade LX-80 Mount
by Fred Wegener
I’ve never been a fan of cables dangling all over the place; especially at night when the possibility of both personal and equipment-related entanglement is very real and potentially dangerous. There are several blogs online where fellow amateurs are discussing wireless control of their mounts using Bluetooth, but most involve considerable equipment cost and/or complexity. Being an electronic engineer by profession and an avid ham radio operator/electronics tinkerer by avocation, I decided I would see just how cheaply and simply I could do this. The entire setup described in this article was built for less than $40.
(We assume you already have items A and B, or something similar to. If not, the cost just went up a bit!)
- Meade LX-80 mount
- Laptop with Windows XP, Vista, 7, 8
- Homemade equivalent to Meade 505 cable (http://www.weasner.com/etx/autostar/as_cable505.html)
- Serial I/O to Bluetooth converter (figure 1), ordered from a reliable Ebay dealer, (got mine from Ebayer “Scrou9”). On Ebay, search “serial Bluetooth master slave.” You will find several listings, but the unit I ordered was the one that also had the onboard 5v usb input. There are a few Ebayer’s selling these, but I can vouch for Scrou9, and his unit – at the time - was only $17.86 with free shipping!
- Bluetooth dongle for the laptop (figure 2), available from Ebay dealer “Yallstore” for about $2/each with free shipping. Mine worked right out of the package in Windows XP and Vista, but required a software update to work in Windows 7. The dealer supplied the link. Maybe your laptop already has Bluetooth capability?
I chose to run the serial adapter off the external 12 volt battery supply I use for my mount. If you would like to do the same, you will require a way to convert the 12 volts from the battery to 5 volts for the adapter. This may be done using the following parts from Radio Shack:
- Qty 1, 7805 regulator IC - $1.99
- Qty 1, NTE NEV22M25AA, 22mfd @ 25vdc electrolytic capacitor - $0.40
- Qty 1, 10K Ohm, ½ watt resistor (comes in a 5 pack) - $1.19
- (Optional) 276-148, dual, mini project board - $2.49
- (Optional) 270-1801, 3x2x1 plastic project enclosure - $3.49
- SPST switch – I used a small toggle type.(275-324) - $3.69
- Small red LED 276-026 - $1.99
- Qty 1, 1K Ohm, ¼ watt resistor (five pack) 271-1321 - $1.49
Here is the wiring for the regulator circuit:
Be careful to get all polarities correct as shown in figure 4.
Should you choose to go with the mini project board and specified enclosure box, you may cut the board to any dimension that will work for the regulator circuit. If you keep it small enough, you can then creatively mount that circuit and the serial Bluetooth adapter into the 3x2x1 enclosure. Bluetooth is very low power/short range, so be sure whatever enclosure you choose is plastic, or the signal may suffer. The picture below (figure 5), shows my finished adapter.
The only signals necessary for control of the Meade 497 (or Audiostar), are TX, RX and Ground, so I chose to use a 1/8th inch stereo phone jack for my data output to the handbox and wired it directly to the underside of the DB9 connector on the motherboard of the serial-bluetooth converter. A 1/8th inch mono phone jack is used for my 12 volt DC input. Referring back to figure 1, there are two holes, labeled + and -, in between the USB power port and the master/slave switch. USB power is hard to come by in this particular application, so I wired the 5 volt output from the regulator circuit directly to these two holes.
A WORD OF CAUTION: My Bluetooth adapter had a mistake on its motherboard: the TX/RX lines were actually reversed in the board artwork. When powered up, it appeared as though it wanted to work, but would not! Not expecting this sort of behavior on a production device, this one took me awhile to figure out, but once I did, it was easily remedied; I simply reversed the two lines on the “homemade” 505 cable and it worked like a charm.
To further relieve the cabling mess, I built a “box,” using furniture grade plywood, that sits on top of my mount to hold the external battery, Bluetooth adapter and the Autostar handbox (see figures 6&7 below).
All required cables now ride on the mount and are out of the way, with no possibility of tangling.
Both the Bluetooth dongle and the serial I/O adapter are self-installing. Install the dongle first. As mentioned previously, the dongle drivers have to be updated for use with Windows 7 and 8, but worked fine as received in the previous two versions of Windows. After installation, the dongle software installed two icons on my desktop: one for “Bluetooth places” and another for file transfers. Go into “Bluetooth places,” right-click the icon for the dongle device, and turn bluetooth “on.” Next, set the master/slave switch on the Bluetooth/serial adapter to “slave,” then turn it on. It will link through the dongle to your computer and install what it needs to. It sets itself up as Bolutek, (on port “COM 9” on my installation). Now go back to “Bluetooth places,” right click the Bolutek icon, and select “pair.” When asked, the pairing code is simply 1234. The next time you power up, you should only have to right click Bolutek in “Bluetooth Places,” then select “connect.” Assumoing you have the adapter and voltage regulator mounted in a box with an on/off switch, you simply leave the switch on the adapter I the “slave” position, and use the on/off switch for future use. Incidentally, there is a lot of configuration programming capability built into the Bolutek adapter, but its default settings are exactly what the Autostar handbox is looking for.
I use Stellarium as my planetarium software. If you are not familiar with this fine piece of work, it is a very user-friendly, open-source freeware application available at www.stellarium.org . Open the program’s configuration window and select “Plugins – telescope control.” At the bottom of the window you have the option to check a box that will allow Stellarium to automatically load the telescope info on powerup. Once you have made that decision, click “configure.” Under type of telescope, select “Autostar compatible” and tell it to address port “COM 9,” (or whatever port the serial I/O adapter loaded itself as). Once out of that screen, select “telescope 1” (assuming this is the only scope being controlled), and “connect.” You may now exit all screens other than the planetarium screen itself. You can find out more about Stellarium’s telescope control options at: http://stellarium.org/wiki/index.php/Telescope_Control_plug-in
At the telescope, use the handbox control to perform the initial alignment, making sure that its time and date coincide with the ones set in Stellarium. Once alignment is complete, connect the serial adapter’s output to the RJ22 port on the handbox controller and you should be ready to go. Go back to your computer, click an object you would like to view, then depress “ctrl 1,” (where 1 is the number of the telescope in your configuration menu). The mount should slew to the object selected. If so, mission accomplished!
About the Author:
AC5TF (Fred) is a 60-ish kid (the law defines when one becomes an adult, but biologically, we’re all just older children ;<), who has been playing with telescopes and astronomy since he was 8 years old…and still is. By day, he is employed as an electronics field engineering representative for a major DoD contractor. In his spare time, he enjoys ham radio, collecting and restoring vintage two-way radio equipment, tinkering with electronics in general, and wishing he was about twenty years younger and independently wealthy.