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.
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
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.
- 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
- Install ASCOM Platform 6.2 or later.
- Run
NGCAT Focuser Setup.exe. - In your ASCOM astronomy software, select "ASCOM NGCAT Driver for Focuser" from the Chooser.
- Configure the COM port (and optionally a CW weather server URL) in the setup dialog.
- 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
- https://github.com/indilib/indi/blob/master/drivers/focuser/robofocus.cpp
- https://github.com/jbrazio/ardufocus-ascom
GPLv3 — see LICENSE.
No support, no guarantees. This project is only here to help those who want to build their own driver.