Standard Autoguider port to relay interface
Posted 18 March 2013 - 09:00 PM
I have a classic 12" f4.5 Cave astrola newtonian with 2 axis motors but the dec motor is 110vac reversable and the polar axis has a synchronus clock motor that uses an old criterion dyna tracker drive corrector.
SO I have Dec left, Dec right and Polar slow, polar fast.
I have 12 vdc available. I want to drive some isolation relays to switch the motions. 5 watts is max current for the dec so I may use reed relays as they are cheap.
But I dont know if the ST-4 guider port expects to output 5 volt logic level or if its dry contacts. Yes, I know, go look and see, but I'd hate to burn up an autoguider if there is a ready spec for this. Thanks if anyone knows. I have the port pinouts but thats about all I find.
Posted 18 March 2013 - 09:12 PM
Posted 18 March 2013 - 09:27 PM
The Shoestring Astronomy web site has a pretty good paper on the ST-4 interface...
Posted 18 March 2013 - 11:11 PM
Posted 18 March 2013 - 11:51 PM
open collector TTL,
Open collector, yes - but TTL, no. Most mounts present 12VDC to the open circuit so the internal switch is something that can handle 12V at the collector; usually CMOS or an opto-isolator.
Posted 20 March 2013 - 06:02 PM
Posted 20 March 2013 - 06:44 PM
for the op amp circuit when powered by AC. The other would be the inverter stepping up the 12vDC to 120vAC.
In either case the op amp changes the RA drive AC frequency in response to the joystick commands. Joysticks usually have a variable pot for each axis, hoever I was able to wire an Atari joystick up to a Nexstar hand controller to provide manual control for a fellow with MS just using four axis conductors and ground.
Posted 20 March 2013 - 07:19 PM
It assumes a low voltage DC Dec motor, controlling your 110vAC Dec would probably require a couple more circuits like these: http://downloads.deu..._PWM_Line_Vo...
I'd be tempted to look for a DC motor.
This is the Covington Circuit on Veroboard.
Posted 20 March 2013 - 11:18 PM
The Declination motor on a cave astrola has twin opposing synchronus motors on the same shaft. Common neutral lead. 110vac to one coil slews clockwise, voltage to the other gives counter clockwise rotation. the dec hand controller is a box with two buttons that conduct line voltage to one or the other coils.
There is a 110vac synchronus clock drive motor on the polar axis. This is the factory standard configuration.
I also have the optional drive corrector, which has a transistor oscillator with fast and slow buttons in a seperate handset. it takes 12v and inverts it to variable frequency ac. The fast and slow buttons add resistance / capacitance for the one or the other speed to vary the oscillator fast or slow fron the normal 60 hertz tracking rate. So I definitely need two general purpose mechanical relays to switch the 110vac for dec and two small reed relays close to the buttons mounted inside the handset to switch the R/C network for the drive inverter.