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ASCOM driver

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jolo edited this page Nov 12, 2013 · 2 revisions

ASCOM driver is built on the available Visual Basic ASCOM template using Visual Studio 2008. Driver itself has several functions:

  • translates ASCOM commands to the ones that focuser can understand (via RS232 port) and vice versa
  • provides temperature compensation
  • provides simple backslash compensation
  • provides setup dialog where user can set focuser parameters

Driver setup window

COM port serial port where arduino board is connected. Must be configured for 9600 bps.

Max focuser position maximum stepper motor step number achievable when focuser is in the most outward position. Depends on focuser travel length, and actual combined gear ratio. Cannot be negative value.

Stepper speed (pps) maximum allowed stepper motor speed in pulses per second. Cheapest motors can achieve up to 100pps, mainstream motors ranges can be up to 500pps.

Stepper duty cycle (%) when stepper motor is not moving some power can be still supplied, so it prevents motor move under focuser equipment load. If motor does not rotate under load, set it to zero. If it does, usually 10-30% is enough.

Step size (microns) focuser travel length that corresponds to one stepper step. Must be calculated basing on focuser travel length and combined gear ratio. Should be at least 5-10 times less than CFZ of your setup. You can calculate CFZ here http://www.wilmslowastro.com/software/formulae.htm#CFZ. This value is not actually needed anywhere in the driver, but it is required for ASCOM driver conformity.

Temp cycle (sec) temperature compensation cycle period. Probably somewhere between 30 and 300 seconds. Actual compensation is applied when temperature will change more than 0.5 degree (it is equivalent to 6 microns length change of 1 meter steel tube).

Comp. (steps/C) actual temperature compensation coefficient. Positive value means outward focuser move (increase focuser position) with temperature raise, so if tube length grows with temperature we need to put there negative value. Set to 0 means disabling temperature compensation.

Set focuser position valid Com port must be selected before this operation. Sometimes we need to reset focuser position or set to desired value. When we lost synchronization between position remembered in arduino board and actual focuser position, we may want to move focuser to its most inward position and then set this value to 0.

Driver setup dialog does not expose stepper reverse direction option. Since you need to connect stepper motor to the project anyway, you can set up desired stepper direction by proper wiring.

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