A mount controller implementing the Meade LX200 protocol and commanding stepper motors. This allows for any dobson telescope to present itself as an LX200 mount. Support for ASI120MM-S/MC-S cameras is also built in. Using one improves the accuracy of plate solving and allows for accurate push-to capabilities if no motors are used. An optimized solver database has been created for the supported cameras. Note that LX200 mounts generally are RaDec but under the hood this project uses AltAz.
At the moment both the motor support and plate solving support are experimental.
To control a mount, clone the repo, install via pip and then issue
run_lx200_mount
This will run the controller with emulated motors.
In order to run with your own motor controllers, create a
~/.config/pylx200mount/config.json
file according to the configuration JSON schema.
In it make sure to set the module and class_name for your motor controller class(es) and the gear_reduction which represents the angle (deg) for each (micro)step of your motors.
If you use Phidgets motor controllers, like me, then set module to pylx200mount.phidgets.phidgets_motor_controller and class_name to PhidgetsMotorController.
If you want use different motor hardware then create a new subclass of pylx200mount.motor.base_motor_controller.BaseMotorController and implement the following methods:
- connect: connect to a motor
- disconnect: disconnect from a motor
- set_target_position_and_velocity: set the target position [steps] and the maximum velocity [steps/sec] in the motor
Then set module to the python module and class_name to the python class for your motor code.
You can also set the module and class_name for your camera, the focal length of the lens or telescope [mm] and whether or not to save the images taken with the camera to enable plate solving.
Currently only ASI120MM-S/MC-S cameras are supported.
If you want to use a different camera then create a new subclass of pylx200mount.camera.base_camera.BaseCamera and implement the following methods:
- open: open and connect to the camera
- get_image_parameters: get the maximum image size and pixel size from the camera and set and the bit depth
- set_gain: set the gain of the camera
- set_exposure_time: set the exposure time of the camera
- take_and_get_image: take an image with the camera and return it as a numpy araay
Note that the default tetra3 solver database may not work well with your camera.
The idea for using a camera for plate solving came from the PiFinderhttps://www.pifinder.io/ project. The source code is open source and can be found here. For rapid plate solving tetra3 is used, just like in PiFinder. I experimented with plate solving with tetra3 with images taken with an ASI120MM-S camera and a 25 mm CCTV lens. In the end I created a plate solver database using tetra3 for which all those images, that don't show too much trailing due to telescope motion, solve within 150 ms. The name of the db is hard coded in the source code for now but it will become a configuration option soon.
The database was created with:
import tetra3
t3 = tetra3.Tetra3()
t3.generate_database(
max_fov=11.0,
min_fov=7.5,
pattern_stars_per_fov=20,
save_largest_edge=True,
save_as="asi120mm_database",
)It took about an hour on my 2020 Intel MacBook to create the db. Note that the db is not included in this GitHub repo. It can be downloaded here.
As soon as a planetarium application connects to the PyLX200Mount software and the position loop starts, the camera starts taking images. Those images are plate solved using tetra3. The resulting position is returned to the planetarium application.
A sync on a known target with the planetarium application is necessary to determine the camera offset w.r.t. the telescope. As soon as a sync is done in the planetarium position, the sync position in RaDec is converted to AltAz. A picture is taken and solved and the resulting camera position RaDec is converted to AltAz as well. The difference between the two positions is stored. From then on, that difference is applied to the AltAz camera position resulting from yet more images and converted back to RaDec. That corrected position is then returned to the planetarium application which then correctly shows where the telescope is pointing in the sky.
A configuration file for push-to with an ASI120MM-S camera looks like this:
{
"camera": {
"module": "pylx200mount.asi",
"class_name": "AsiCamera",
"focal_length": 25.0
}
}A configuration file for GOTO with Phidgets motor controllers looks like this:
{
"alt": {
"module": "pylx200mount.phidgets",
"class_name": "PhidgetsMotorController",
"hub_port": 0,
"gear_reduction": 0.00005625
},
"az": {
"module": "pylx200mount.phidgets",
"class_name": "PhidgetsMotorController",
"hub_port": 1,
"gear_reduction": 0.00005625
}
}A configuration file GOTO with Phidgets motor controllers and an ASI120MM-S camera for plate solving looks like this:
{
"alt": {
"module": "pylx200mount.phidgets",
"class_name": "PhidgetsMotorController",
"hub_port": 0,
"gear_reduction": 0.00005625
},
"az": {
"module": "pylx200mount.phidgets",
"class_name": "PhidgetsMotorController",
"hub_port": 1,
"gear_reduction": 0.00005625
},
"camera": {
"module": "pylx200mount.asi",
"class_name": "AsiCamera",
"focal_length": 25.0
}
}Here are instructions to set up some popular planetarium applications on the computer or mobile device from which you want to command the mount.
In all cases, the connection must be set to Wi-Fi/Ethernet using the IP address of the computer running PyLX200Mount and port 11880.
In the menu bar click Telescope and select Setup...
Set the following properties:
- Scope Type:
Meade LX200 Classic - Mount Type:
Alt-Az GoTo - Connection:
WiFi or Ethernet (TCP/IP) - Readout Rate:
2 per second
Enter the IP address and port as indicated above and click the Connect button on the bottom left.
Open the settings and scroll down to Telescope Presets.
Press the + Add Preset button.
Select Other.
Set the following properties:
- Mount Type:
Alt-Az GoTo - Scope Type:
Meade LX200 Classic
Press Next... to the upper right.
Enter the IP address and port as indicated above and press Next... to the upper right.
Set Readout Rate to 2 per second.
Enter a name if you like and press Save Preset.
Back in the main screen, press the Scope button and then the Connnect button.
Open the Telescope Resources and either select an exisiting telescope or add a new one.
Under Computerized Mount (if applicable) select Meade: LX200 Classic.
Click the Edit button.
Enable Use WiFi-to-Serial adapter or TCP/IP and set it to Direct TCP/IP.
Set WiFi-to-Serial adapter or TCP/IP address to the IP address and port as indicated above.
Under Coordinates enable both Convert coordinates TO mount to current epoch and Convert coordinates FROM mount to current epoch.
Press OK and close the Telescope Resources dialog.
Select the telescope you just configured and toggle Connect to telescope.
I am working on support for an INDI profile, so it can be used with a stand alone INDI server. Until then KStars needs to be used.
In KStars, press CTRL-SHIFT-D to open the device manager.
Under Telescopes, select either LX200 Basic or LX200 Classic.
Click Run Service.
Open the Connection tab and set the Connection Mode to Network.
Enter the IP address and port as indicated above and click the Set button to the right of them.
Open the Main Control tab and click Connect.
In the menu to the top left, select Observing Tools and enable Telescope Control.
Enter the IP address and port as indicated above.
Toggle the switch to the right of Link.