Computing#

telescope-pi#

The telescope-pi computer is a Raspberry Pi located inside the white electronics box in the telescope tube. Currently it provides a small TCP server that controls the filter wheel. The Raspberry Pi is connected over USB to a Phidgets motor controller that moves the filter wheel, and over USB-to-serial to an Arduino that reads the Hall effect sensors that encode the position of the wheel.

Setting

Value

IP

72.233.250.84/26

Hostname

telescope-pi.mro.cwu.edu

Gateway

72.233.250.65

User

mrouser

Password

<usual-password>

Software#

telescope-pi only runs the evora-wheel as a Docker container. The container is configured to always restart. The wheel server can be accessed on port 9999 and accepts the following commands

Command

Action

get

Returns the 0-indexed position of the wheel

move X

Moves the wheel to the X position

home

Homes the wheel (after homing the wheel will be at position 0)

After a command has been accepted, the server returns OK followed by comma-separated return values, if applicable. For example, get will return OK,5. If an error occurs, the server will return ERR,<error-description> where <error-description> is a human-readable description of the error. After a command has been processed, the server always closes the connection to the client.

Updating and restarting the software#

The easiest way to restart the software is power cycle the Raspberry Pi. The server will start again after booting. To update the software or restart it from the command line, ssh to mrouser@72.233.250.84 and execute run-wheel. This will stop the current container, pull for new Docker images, and create a new container that with restart policy always.

Setting up telescope-pi#

To set up a new telescope-pi from scratch, start with a blank micro SD card (16 GB should be enough). Flash the desired OS. The current telescope-pi uses the headless server Raspberry Pi OS 22.04 LTS which can be installed using the Raspberry Pi Imager. During this stage you may want to click on the gearbox icon and set up the hostname, enable SSH, and defined the username and password.

You will need to connect the Raspberry Pi with the newly flashed memory card to a router with a DHCP server and determine the assigned IP. With a computer in the same network ssh to the RPi with ssh mrouser@<assigned-IP>. Once inside the computer, follow these steps:

  1. Set up Docker. Generally follow these instructions. Once you have confirmed that sudo docker run hello-world, allow the mrouser user to access the Docker daemon by doing sudo usermod -a -G docker mrouser.

  2. Edit ~mrouser/.bashrc and add the following line at the end

    alias run-wheel='docker stop evora-wheel; docker rm evora-wheel; docker pull ghcr.io/uwmro/evora-wheel:latest && docker run -d -it -p 9999:9999 --name evora-wheel --restart always ghcr.io/uwmro/evora-wheel'

    This alias will stop the currently running evora-wheel container, remove it, pull for a new image of the product, and then run it with restart policy always and expose it to port 9999 of the host computer.

  3. Log out of the RPi and log in again. Then run run-wheel. It should pull a new image and finally run the container. Connecting to the server at this point will fail since it is not connected to the filter wheel.

  4. Change the network configuration. Edit the file /etc/dhcpcd.conf and add the following at the bottom

    interface eth0
static ip_address=72.233.250.84/26
static routers=72.233.250.65
static domain_name_servers=8.8.8.8 8.8.4.4

    Note that once you restart the RPi with this configuration you won’t be able to access it again unless you’re at MRO or you configure a network in the 72.233.250.0/26 range.