Wednesday, 25 February 2015

Give your telescope some teeth

I recently bought a new mount for my Celestron C6 telescope. I am now the proud owner of a Celestron Advanced VX mount. I've not had it outside yet (its still a balmy -10C outside!) but I'm very pleased with its stability and ease of use. I have it set up in my basement and have been getting all the remote control software organised for it so that I can try my hand at some astrophotography when the weather breaks.

As you can see it has a hand controller that will allow me to manually drive the mount to any of over 10000 objects. But for taking pictures I need to have computer control. Luckily this mount comes with that already enabled by way of a RS232 cable that plugs into the bottom of the handset. Only 2 problems here; 1) I have no serial port on my laptop, 2) I must be "tethered" to the mount. I dunno about you but I'd rather have the least amount of cables dragging around my equipment especially when its dark and I can't see them. So wireless is my goal.

One can buy a WiFi enabled remote control device that plugs into the mount but its $100 and as it's WiFi it'll quickly kill the batteries of any mobile device I use with it in place of the PC. Bluetooth is the solution that springs to mind. It has a serial port emulation ability and uses much less power than WiFi.

Other owners have had this idea too. I've seen some interesting attempts to add Bluetooth abilities to this mount. Most of them are a lash up of common off-the-shelf parts and added wires. This solution costs over $130. So whilst sitting on the pot the other day (I do my best thinking in there) I had an idea , "why not connect something directly to the Aux connector on the mount?". Looking at the wiring diagram for the connector we can see that there is 12V of power and 5V TTL serial data available. Indeed, this is what the WiFi adapter uses for it's power and comms as does the GPS receiver addon.

This is what I came up with. One adds a 6 pin telephone cord between the adapter and the Aux socket at which point it'll spring to life. The missing part on the board rendering above is an HC-06 Bluetooth interface. The rest of the stuff is power conversion and such like. Following the "howto" I installed the relevant software and was able to control my mount from my PC. I've also tried it with Sky Safari on my Android tablet too. Works perfectly! I can even remove the hand controller from the mount which will help when up at the club site preventing visitors from playing with my scope when I'm not looking.

False Teeth under test
I'm calling the project "False Teeth" as the device is not blessed by Celestron.

Files in Eagle format ...
False Teeth.pdf
False Teeth.sch
False Teeth.brd


  1. Hiya Mark i hope you maybe able to offer some advice,

    Im curently trying to set up an ESP8266 serial wifi module to connect in the similar way the bluetooth does,

    I have a Nexstar+ and would like to use the celestron sky portal app on my iPhone however it only supports Wifi and not bluetooth.

    Hope you can help,

    Thank you Rick

  2. Hi Mark. I decided to undertake a similar project but am using the SparkFun BlueSmirf as the base unit as the level conversion is already taken care of on the board. Everything is wired up and running from the +12V provided at the AUX port, but the hand controller seizes up randomly and I can't talk to the scope via BT either. When I disconnect the TX line from the BT module the HC comes back and I can read data from the scope in hyperterminal. I'm hoping you could give some insight on any additional configuration you made to the HC-06 in order to get comms working. Thanks.

    1. Look at my diagram. You'll see that not only do I do signal level conversion but there is a sort of RTS/CTS mechanism too. I _think_ your HC issues are caused by concurrent conversations on the serial bus. You need to make sure that only one device is using the comms bus at the same time.

    2. Hi Mark, I cannot see that you are using RTS/CTS on your board! Anticipating you are running over AUX port, the doc tells 19200 baud. Is this correct ? also what software are you using to pilot your telescope over BT ? (I am able to remote control over RS232 cable, but not over any wireless). Tks for any hint !

  3. Hi Mark. Brilliant design. So much better than the other ideas out there. Any chance of buying one of these off of you? I’d be happy to solder one up myself, but don’t have ready access to board and components where I live (Philippines).

    One side thought - is there a board mountable plug (rather than jack) available, so the unit could be plugged straight into the Aux jack without the little patch cord? Regards, Peter

  4. Hi Mark, any chance to send one of this adapters to me?

    I am very interested on your device, please send me a message and we could talk about it.

    thank you in advance

  5. Hi Mark. I was finally able to obtain the boards and all the components and finished assembling the unit. It powers up fine and no problems with pairing. Initially it connected with my phone and tablet after the initial pairings, but after that it won't connect to either any longer even if I unpair, reboot and start again. I can run a bluetooth terminal program on the tablet and it will connect (steady led), however it doesn't output OK in response to AT. As soon as I leave the terminal program the led returns to blinking and won't connect to either device, but will reconnect to the terminal program once run again.

    Would you have any idea as to what the problem is and how I should go about addressing it? I've read everything I could find on the HC-06 module, but found no clues as to this problem. Any guidance you could provide would be greatly appreciated.

    Thanks & regards, Peter

  6. Hi Mark,

    I was able to get the board to connect to my PC and configured it in Stellarium, however the scope still doesn't respond to commands. Upon observing the HC I note that within 20-30 seconds after the board is plugged into the Aux port the HC displays a No Response 17 error, even with no other actions done. Clearing this (pressing back a couple of times) it just happens again after another 30 seconds or so. Either 17 or 16 error. If I clear the error and try to slew the scope with the board plugged in it keeps going in whatever direction I start it in (even after releasing the slew button on the HC) until I hit the back key. I perform an alignment first before plugging the FT board in.

    I also tried with the HC unplugged from the scope (after aligning) and no response to slew commands from Stellarium.

    Does this behavior indicate that there is something wrong with my board, or perhaps the connector cable? If not, what would you suggest as trouble shooting please?


  7. Mark, another possible clue - if I have the board plugged into the aux port when I turn the scope on, in addition to the "No Response 17" error it says "Invalid model" and after hitting Back a couple of times it displays Nexstar GPS at the top. It appears that the scope thinks my board is an incorrect version of the Nexstar GPS module that can be used in the aux port. Don't know if that's a useful clue or not. Regards.

  8. One more clue - with the board plugged in if you try to display the firmware version numbers on the HC you will see the HC version correctly, but the MC version reports as all question marks. Unplug the board and redisplay the version numbers and they report just fine.

  9. Interesting. I notice you aren't using the hardware flow control (RTS/CTS) pins. Does this mean the Celestron's AUX port supports software flow control?

  10. Man, and I thought my bench was bad!