If you want to roll your own focuser controller, it uses the same commands as the motor controllers (including goto, get position, and backlash settings) as the motor controllers. The AuxBus address of the focuser is 18 (0x12). There are 3 additional aux bus commands you might want. CALIBRATION_ENABLE 0x2A // takes 8 bit data value. Clears calibration data. If Value != 0, also starts calibration process. IS_CALIBRATED 0x2B // returns 8 bit data. true (0x01) if calibration is complete, false (0x00) otherwise. GET_CALIBRATION_POSITIONS 0X2C // MC returns 2 uint32_t (8 bytes total) for the low side and high side limits. (typically < 65535). Big endian.
One benefit is not needing to occupy another USB port, especially if you are running on a RPi (or Rcok64 in my case) and already taking up a lot of ports. On nights when I am not imaging, I’d still be able to motor focus without needing to hook a computer or battery up to the focuser. I also like to tinker, which is probably the best/honest reply.
ChrisRowland wrote: ... but I don't see any benefit, especially as the Arduino already has a perfectly good USB interface that allows it to connect independently. The internal protocol uses the same commands but is different to the passthrough protocol used by the HC.
ChrisRowland wrote: Yes, using the same port as used by the telescope in much the same way as the Meade does.
Yes, it's the same passthrough commands as the telescope axis motors. I chose not to implement backlash and calibrate, I see calibrate in particular as something that's better done by the Celestron software. What it does is to move to each end of the range looking for the hard stops. When it finds them it remembers their position.
For the question about using an Arduino based focuser, in theory it would be possible to connect it to the mount internal bus and reverse engineer Celestron's internal bus protocol but I don't see any benefit, especially as the Arduino already has a perfectly good USB interface that allows it to connect independently. The internal protocol uses the same commands but is different to the passthrough protocol used by the HC.
Scanner001 wrote: I have this focusor and do not use it with a Celestron mount so independent focus control outside the mount is needed.
I will manage the focusor via USB connect directly to my RasberryPi running StellarMate.