DIY Virtual Electronic Finderscope

StarPointer is a virtual electronic finderscope for astronomical telescopes. This device works with Stellarium and helps the observer identify objects in the sky.

This unit can be attached to the telescope without modifications and connects with the computer through the USB port. The StarPointer uses a few onboard sensors to determine its angle and position. After obtaining that information, the unit calculates the RA (right ascension ) and DEC (declination) coordinates of the telescope and transfers those details to the Stellarium.

• 1MΩ (SMD 0805) : Quantity - 1
• 100KΩ (SMD 0805) : Quantity - 2
• 10KΩ (SMD 0805) : Quantity - 1
• 680Ω (SMD 0805) : Quantity - 1
• 1.5KΩ (SMD 0805) : Quantity - 1
• 22Ω (SMD 0805) : Quantity - 2
• 22pF (SMD 0805) : Quantity - 2
• 15pF (SMD 0805) : Quantity - 2
• 0.1μF (SMD 0805) : Quantity - 9
• 0.01μF (SMD 0805) : Quantity - 1
• 1μF (SMD 0805) : Quantity - 2
• RED LED (SMD 0805) : Quantity - 1
• 5mm Axial Ferrite Bead : Quantity - 1
• 32.768kHz Crystal (AT-310) : Quantity - 1
• 8.00MHz Crystal (HC-49) : Quantity - 1
• CR1220 Battery Holder : Quantity - 1
• XM7D-0512 - USB Mini-B connector : Quantity - 1
• STM32F103C8T6 : Quantity - 1
• USBLC6-2SC6 : Quantity - 1
• RT9193-33GB : Quantity - 1
• ADXL345 Module : Quantity - 1
• HMC5883L Module : Quantity - 1

In addition to the above components, the following modules and tools are required to flash and test this unit:

• ST-Link/V2 programmer
• 3.3V USB to TTL serial adapter

The printed circuit board (PCB) of this module is designed using KiCAD. The dimension of the PCB is 82.5mm × 22.5mm. To build this PCB we used, 1.6mm FR4 board with a 1oz thickness of copper.

PCB of this project is fabricated by using PCBWay. The original version of this PCB is available to order at the PCBWay project directory.

The StarPointer printed circuit board uses both surface-mounted and through-hole type components. To minimize soldering difficulties, we recommended soldering all the SMD components first.

All the above soldering steps are clearly shown in the video available in this section.

The StarPointer builds around the STM32F103C8 microcontroller, ADXL345 3-axis accelerometer, and HMC5883L 3-axis magnetometer. This unit communicates with the PC using the inbuilt USB peripheral of the STM32F103C8 microcontroller. The firmware of the StarPointer is developed using the LibOpenCM3 library and built using GNU ARM Embedded Toolchain.

The compiled firmware binary is available to download in the release section of the project repository.

To flash the firmware connect ST-LINK/V2 USB programmer to the J2 ICP port.

This unit can attach to any astronomical telescope or binocular regardless of its type or mount. After attaching the unit, the user needs to calibrate the StarPointer using the configuration software. This configuration software allows StarPointer to set the latitude and longitude of the observation location, RTC date/time, and RA and DEC offsets. After performing the above steps, the unit is ready to use with the Stellarium.

StarPointer sync tool is a GUI application and it supports both Linux and Windows operating systems.

Compiled binaries of the StarPointer sync tool are available to download at the release section of this project repository.

The StarPointer is designed to work with Stellarium's telescope control plugin. Its firmware has been developed to work with the Meade LX200 communication protocol, and no additional modifications are needed for Stellarium to work with this sensor kit.

The configuration steps are listed below:

1. On the main screen, press the Configuration Window button (or F2).
2. Select the Plugins tab.
3. Find the Telescope Control plugin and tick the Load at startup checkbox.
4. Restart the Stellarium.
5. Click the telescope icon at the bottom of the Stellarium screen. (or press Ctrl + 0)
6. On the "Slew telescope to" window, press the Configure telescopes... button.
7. Click Add a new telescope button.
8. Enter the following values to the "Add new telescope" window:

• Telescope controlled by: Stellarium, directly through a serial port
• Telescope name: StarPointer
• Coordinate system: Equinox of the day (JNow)
• Serial port: select the serial port which connects the StarPointer sensor kit
• Device model: Meade LX200 (compatible)

The above configuration should be done only once. After setting up the StarPointer as a telescope, the user can start the sensor kit as follows:

1. Click the telescope icon at the bottom of the Stellarium screen. (or press Ctrl + 0)
2. On the "Slew telescope to" window, press the Configure telescopes... button.
3. On the "Telescopes" window, select StarPointer and press the Start button.

We also design a suitable enclosure for this project, and its design files are available to download at tinkercad.com. This design can be 3D printed using either ABS or PLA. To get the optimal results, we recommended attaching this enclosure to the piggyback bracket of the telescope.