Ascom Alpaca Device Driver for 1m Ash Dome at Apache Point Observatory

Implement a simple Alpaca driver for 1m Ash Dome, using the Autoscope dome control box. This box has relays that allow for power on/off to dome rotation motor and shutter motor, and relays that allow for change of motor direction on each of these. The system also has a watchdog input, such that if power is dropped on the watchdog, the dome shutter will close automatically. The system also has relay to switch between manual and automatic mode; computer control only enabled under the latter. Separately from the motor control, there is an encoder on the rotator gearbox, and a magnetic home sensor.

Motor control

Specifically, computer control is implemented through four connectors on the right side of the dome control box:

Relays are triggered by closing circuit to bring relay line to ground. Need to confirm below which pins are ground vs which ones are relay control.

• J805A : supplies power and control for dome rotation power
  • Pin 1: shield
  • Pin 2: dome power relay ?
  • Pin 3: gnd ?
  • Pin 4: +24V
• J806A : supplies power and control for dome rotation direction
  • Pin 1: shield
  • Pin 2: dome direction relay ?
  • Pin 3: gnd ?
  • Pin 4: +24V
• J807A : supplies control for shutter rotation and direction
  • Pin 1: shield
  • Pin 2: shutter power relay ?
  • Pin 3: gnd ?
  • Pin 4: shutter direction relay?
  • Pin 5: gnd ?
  • Pin 6:
  • Pin 7:
  • Pin 8:
  • Pin 9:
• J808A : supplies +24V from watchdog
  • Pin 1:
  • Pin 2:
  • Pin 3:
  • Pin 4:

Encoder

Dome position is read separately from a quadrature encoder, hooked up directly to the Raspberry Pi. This gets +5V from the computer, and returns +5V signals, which must be level-shifted to 3.3V before input to RPi GPIO pins. Changes in level are detected using pigpiod; separation of typical pulse times are several hundred microseconds.

• Pin 1: +5V
• Pin 2: gnd
• Pin 3: Bbar
• Pin 4: B
• Pin 5: Zbar
• Pin 6: Z (index)
• Pin 7: Abar
• Pin 8: A

Home sensor

Setup for Raspberry Pi:

• enable VNC, SPI
• python -m venv venv
• pip install falcon toml ipython pi-plates spidev RPi.GPIO pigpiod
• pigpiod daemon must be running: sudo pigpiod -s 10 (sampling rate of 10 microsec is fine)

Software routines

Alpaca driver implemented in app.py and dome.py

APO routines are implemented in Dome class in APOAshDome.py and Encoder.py