Convert ST-4 to Celestron RS-232

[sgazer]

hi all,

not been on for a while, but I was hoping you could help me please.....

I have a Celestron SE4 which I would like to try to auto guide without using a laptop. The SE4 mount doesn't have an ST-4 port, only the RS232 port in the handset which I currently connect to the laptop to control the mount.

All the standalone auto guiders only seem to interface to ST-4 ports. Is there anything which can convert the ST-4 signals to Celestron RS-232 signals and commands to move the scope? It's a relatively simple thing to do, but I can't find anything ready made.

Many Thanks.

[kalasinman]

Would this work?

http://www.optcorp.com/celestron-rs-232-cable-for-nexstar-cge-mounts.html

-Jack

[sgazer]

Thanks but unfortunately not, it just takes rs232 from the laptop to the celestron handset, I need to convert st-4 signals to rs232.

Probably something like this, but for celestron

https://docs.google.com/viewer?url=https://www.ioptron.com/images/up/ST-4_Adapter1.pdf

[kalasinman]

Although I haven't done it, I've read this sort of cable is plugged into the handset plug on the mount and the ST4 plug on the guider. Just a thought, sorry I can't be more helpful.--Jack

[Cornelius Varley]

The reason the mount doesn't have a st4 port is because it is an alt az and as such isn't suitable for auto guiding. The mount does has a built in wedge which should allow for longer exposures ,but I doubt that it is capable of being auto guided with any degree of success.

[sgazer]

hmm, yes, but it's basically a slightly lower end version of the SE6/8 which do have guide ports. It has pretty good tracking and I've used in EQ mode fairly successfully up to about 400mm FL and 60s exposure, which is the max I can use with my FZ200 camera (at F2.8 it captures quite a bit). I tried autoguiding though the handset, which also worked well, but I wanted to do away with the laptop and use a standalone auto guider.

It seems there isn't going to be anything off the shelf. I can either convert the camera port into an ST-4 port and control the motors directly using some FETs or it might be possible to (get someone to) programme a simple device we have at work which should be able to read in the 4 digital (ST-4) states and spit out RS-232 commands to the handset. I've found the Celestron protocols and messages on the internet. But that's all a bit of work and a few favours needed. It would be nice if something already did it.

[sgazer]

hmm, yes, but it's basically a slightly lower end version of the SE6/8 which do have guide ports. It has pretty good tracking and I've used in EQ mode fairly successfully up to about 400mm FL and 60s exposure, which is the max I can use with my FZ200 camera (at F2.8 it captures quite a bit). I tried autoguiding though the handset, which also worked well, but I wanted to do away with the laptop and use a standalone auto guider.

It seems there isn't going to be anything off the shelf. I can either convert the camera port into an ST-4 port and control the motors directly using some FETs or it might be possible to (get someone to) programme a simple device we have at work which should be able to read in the 4 digital (ST-4) states and spit out RS-232 commands to the handset. I've found the Celestron protocols and messages on the internet. But that's all a bit of work and a few favours needed. It would be nice if something already did it.

Just quickly looking at a few teardowns in the internet, it seems the motors are stepper motors, which would be a bit more difficult to control. So I think the ST-4 to RS232 conversion might be the best way.

[Cornelius Varley]

You may be able to find a bit more information here http://www.nexstarsite.com/ . I think the motors are DC servos not steppers.

[sgazer]

You may be able to find a bit more information here http://www.nexstarsite.com/ . I think the motors are DC servos not steppers.

yes, you're right, I just opened it up and they are indeed DC servos, the other wires I saw must have been for the position sensors. In which case, it would make it relatively easy to switch over from mount controlling the motors to the ST-4 port controlling them (via a driver interface). It would still maintain it's position reference too, it just wouldn't be moving the mount.

Another option I thought of is; I've got a Windows 8 tablet on it's way from China. If this is powerful enough to take a video input via USB and run EQmod to control the mount (USB to serial - serial to handset), it could be another portable option. I did succeed with this using a 700MHz Pentium III laptop several years ago, and I reckon Intel's new Bay Trail CPU is better than that! I've not used Windows 8 before with all this astro gadgetry, so I'm sure that will be a challenge too, with stuff that worked on XP not working any more!

[orly_andico]

use an Arduino.  The ST-4's are just pull-downs, you can read them using the Arduino digital input lines (just enable the internal pullup).

e.g. RA+ to Arduino pin D7

RA- to Arduino pin D6

DEC+ to Arduino pin D5

DEC- to Arduino pin D4

the ST-4 ground should be connected to Arduino ground.

Now in your loop, just digitalRead(D4... D7) to read the ST-4 inputs.

You will need to attach a MAX232 level converter to D0 and D1 (which are the Arduino RX and TX).  Also you will need to do a bit of poking into the Celestron serial protocol.  The concept is, use the Arduino to read the ST-4 inputs, then output the appropriate PulseGuide serial commands to the serial port.

Note that you will need to have the MAX232 on a separate shield (because D0 and D1 are also used to program the Arduino, you will need to program the Arduino with the MAX232 disconnected, then power off, attach the shield, and power on again).

The whole process is a pain and you'll have to do some soldering, but it is fairly straightforward.

[sgazer]

thanks, that's another good option, similar to the little programmable device we have at work. I'm an electronics engineer and haven't done programming for a while, the guy who programme this device is on holiday for 3 weeks. Another guy at work is a fan of Arduino's though.

The Celestron protocols seem pretty simple, basically 4 commands to slew in each direction with a specified speed.

In the mean time, as my Windows 8 tablet is arriving this week, I think I'll pursue this method initially and see how it works out. A 10" tablet would be a good replacement for a laptop, sitting on nice bracket and running carte du ceil to control the camera direction. I used to use Guidedog for guiding, not sure if it will work on Win8, but it seems PHD has been updated to do so, so I might switch to that.

It looks like Ascom will work with Win8 too, so it's the USB-serial adapter drivers and video capture drivers that I need to check, plus of course the capabilities of the tablet.