Gerald's Astrophoto Gallery


An ASCOM/RoboFocus protocol compatible focuser driver for unipolar stepper motors

FreeFocusHaving a Hurst stepper motor in spare, I built the stepper motor controller circuit from and rewrote the firmware (Atmel AT90S2313) to mimicry a RoboFocus controller (without temperature compensation). I also added to buttons to allow manual control of the focuser.



Standalone operation using built-in buttons, running the motor at slow or high speed.

  • (Nonlinear) acceleration ramping
  • Half step – high torque stepping
  • All parameters are permanently stored in EEPROM
  • RoboFocus compatible protocol – to control the focuser use the free downloadable “RoboFocus Control Program” (RFCP) which is ASCOM compatible and supports ActiveX scripting
  • Simple and cheap to build

March 1, 2006  

SBIG DC/DC 12V Converter

A cheap, simple, small, secure and lightweight DC/DC converter for SBIG ST7/8/9/10/2000 CCD cameras

This small circuit delivers +12V (direct connection), -12V (125mA) and +5V (3000mA) which are necessary to drive a SBIG ST-X series CCD camera and also supports safety protection like inverse polarity, overload, overcurrent or short circuits. To avoid any noise from other devices, the input is filtered with some caps, totalling in 1600µF.

The original circuit is from Takashi Ohta, Japan but I used other parts which were available in Austria.

Total cost: ~70.00 €SBIG DC/DC Converter

March 1, 2006  

SBIG Optocoupler

Convert the ST7-RC telescope adaptor into an optical isolated optocoupler

When running camera and telescope controller from the same battery - and also connecting the autoguider cable between them - you might toast your thousands bucks equipment. Build this ~5.00 € circuit and prevent yourself from heart attacks!

Optocoupler Optocoupler Optocoupler BoardSchematic

I downsized the circuit from Dave Lakey ( and got it small enough to fit into the ST7-RC adapter (part of every ST camera) and thus converts this piece into an optocoupler.

March 1, 2006  


TupperHubThis replacement for the original Losmandy controller contains:

  • Boxdörfer MTS3-SDI with
    • LC Display
    • Encoder IC with separate 5 Volts supply and DB-9 connector
    • Handbox/Autoguider RJ11 connector
    • External MTS Port
    • USB-RS232 converter
  • 12 to 24V converter (for MTS3-SDI)
  • USB 4-port hub
  • USB 2-port hub + RS232 converter


Because of the vast number of cables between those items I just put them together in a Tupperware box, and mounted it to the Losmandy G-11.

Finally, the number of cable connections have been drastically reduced. I also plan to put the Focuser circuit and the SBIG DC/DC converter into a new and better built version of this box.

March 1, 2006