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ASCOM.NGCAT.Focuser

RoboFocus controller through ASCOM — a custom IFocuserV2 driver for the RoboFocus serial protocol.

Having a RoboFocus, I ran into a few problems with the various drivers I could find:

  • v1 drivers didn't have access to temperature.
  • v3 drivers have temperature but don't save settings well and are a bit unstable.

Lack of development from the manufacturer for many years means the focuser is abandoned. So I found old documentation that mentions the protocol and implemented my own.

Architecture

Architecture Diagram

The driver implements the ASCOM IFocuserV2 interface as a COM-visible .NET assembly (C#, .NET Framework 4.8). It talks to the RoboFocus over RS-232 serial at 9600 baud with 9-byte checksummed messages. Temperature can be read either from the focuser itself or from a weather server (via an optional CW HTTP endpoint providing cloud, temperature, humidity, dew point, etc.).

Interactive HTML version: architecture.html

Protocol

The RoboFocus serial commands are:

Command Direction Description
FG ↕ Get current position / Set target position
FT ↕ Get temperature (raw ADC steps)
FV ↕ Get firmware version / Start ADC reading
FQ ↓ Stop motion (emergency halt)
FP ↕ Power module status
FB ↕ Backlash compensation (mode + amount)
FL ↕ Maximum travel limit
FC ↕ Configuration (duty cycle, step delay, step size)
FS ↕ Sync position (set current position counter)

Messages are 9 bytes: 2-byte command + 6-byte payload + 1-byte checksum (sum of ASCII values mod 256). Responses begin with F (+ a two-letter command code) followed by 6 numeric bytes.

Features

  • Absolute positioning — position range 0 to 10,000 steps, maximum 10,000 steps per single move
  • Temperature reading — from the focuser directly, or optionally from a remote weather server if a CW URL is configured
  • Temperature compensation — not implemented (the RoboFocus hardware doesn't support it natively)
  • Multi-client serial — shared serial port with reference counting, so multiple ASCOM clients can connect without fighting over the port
  • Position sync — manually set the current position counter from the setup dialog
  • Tracing — file-based logging to C:\temp\Focuser.log (enable via setup dialog)
  • Inno Setup installer — 32/64-bit COM registration via regasm /codebase

Setup

  1. Install ASCOM Platform 6.2 or later.
  2. Run NGCAT Focuser Setup.exe.
  3. In your ASCOM astronomy software, select "ASCOM NGCAT Driver for Focuser" from the Chooser.
  4. Configure the COM port (and optionally a CW weather server URL) in the setup dialog.

Requirements

  • Windows (COM / .NET Framework 4.8)
  • ASCOM Platform 6.2+
  • RoboFocus unit connected via RS-232 serial
  • The CW weather server is optional — only needed if you want weather-based temperature readings

Sources

License

GPLv3 — see LICENSE.

No support, no guarantees. This project is only here to help those who want to build their own driver.