Before you start, I have been using this mod for sometime now and have experienced HC bootloader errors. It only happens when SkySafari is connected to the HC and SkyAlign is selected then when local time is displayed and back button is pressed the HC will black out and power cycle will have Bootloader Pkg Error 0040 displayed. The only way to bring the HC back is to reflash using CFM.
I don't know if the HC firmware or SkySafari has a bug that causes this, but it will only happen when SkySafari is connected. When using the HC by itself or when the mount has been aligned and SkySafari is connected there are no problems. I believe it has something to do with time and location sync between the two.
I managed to get myself a Celestron Nexstar 90GT for cheap. The scope works and so is the handcontroller, alignment was easy and its Go-To capabilities seems ok.
I've seen that nexstar scopes can be controlled by a PC using RS-232 interface and programs like NexRemote, skychart and others.
This instructable shows how to use garden variety slave bluetooth modules from ebay, particularly the HC-06 module.
1. Opening and/or modifying your HC will void your warranty
2. Be aware of ESD damage on sensitive components while working inside your equipment.
2. This instructable requires soldering small components/wires and cutting thin PCB traces. If you're not into it then might as well leave your HC as is. Any damage you do on your HC is your responsibility.
What you need:
1. Celestron Nexstar hand controller (HC)
2. HC-06 slave bluetooth module
3. Wirewrap wires
1. Soldering iron suitable for SMD work
3. Screw driver
4. Xacto hobby knife
The image shows the HC06 with an RS-232 converter connected to the HC. This setup works without problems but if you dropped the HC the module might get damaged. What we intend to do is to put the module inside so that it can be protected and make the HC look stock.
Signals at the HC bottom connector is actually standard RS-232 level. You can gain access to it via an RJ-22 connector. Celestron sells this cable that will allow a PC to control your telescope and update the HC's firmware.
Inside the HC there is a chip that generates this RS-232 level (Sipex SP3232ee). Since the bluetooth module operates on logic level serial, we need to get around this chip. The best way is to check the datasheet.
The board uses pins R1OUT, T1OUT, R1IN, and T1IN on SP3232 for the interface and RX1 (pin38) and TX1 (pin37) pins on PIC18F85J10 MCU.
We could not connect directly to the RX1 (pin38) on the PIC chip. Doing so would short both SP3232 and bluetooth output pins and one of or both them might get damaged. The best solution for this is to cut the PCB trace.
Start by scraping the solder mask on the trace (under D22 label on the picture), then cutting the trace so that the RX1 on the PIC and R1OUT on the SP3232 is isolated. Cut carefully so that you do not damage any other trace nearby, I would suggest doing this under a well lighted magnifier so that you can see clearly what you're doing.
T1IN pin on the SP3232 is an input we can tap the bluetooth module RX pin to it since it is also an input line.
Next we solder small wires to the scraped PCB traces in order to gain access to the PIC pins and allow us to connect to the bluetooth module.
Complete the module wiring. 5V power is taken from one of the regulators (U9) on the main board to supply power to the module.
Currently the unit works with SkySafari app for Android. The RS-232 interface at the bottom of the HC is currently not connected. I plan to put a small sliding switch between the bluetooth and SP3232 chip so that I can switch between wired and wireless connection.
Some future plans:
1. Switch between wired and wireless connection
2. Replace the SMD LED on the bluetooth module with a 3mm LED and drill a hole on the case so that the HC-06 status can be viewed externally.
3. Change the Bluetooth name from HC-06 to Nexstar ( should have done it before wiring the module)