Adding ST4 to an antic Vixen Polaris MD5 quartz controller?

[Fred_76]

Hi.

I own an antic Vixen Polaris with its original MD-5 Quartz controller.  Does anyone have an idea how I could add ST4 possibility to this controller ?

There are only 3 buttons :

• Stop
• x2
• x8

This idea is to link the Stop button to the RA- ST4 pin, and x2 button to the RA+ ST4 pin. Would this work if I just link the buttons like this, or do I need a more complex electronic mount (with optocouplers, resistors...).

Clear sky

Fred

[windjammer]

Yes, that is about right.  I presume the normal mode if no button pressed is to run at the sidereal rate.

I have been round a similar loop as this.  I would be very wary about attaching bits of kit to each other - eg are there any voltages you don't know about on the Vixen switches when you tap onto them.  I think the ST4 from something like a ZWO cam is just open collector that conducts to the ST4 common but I have no idea what the current limits are.  Which bit of kit do you power up first etc etc.  So a small risk that expensive bits of kit could get fritzed!

I built this ST4 fanout box for just this issue - some pics and a (rather scrappy) circuit diagram attached.  The ST4 signals are buffered and used to switch simple reed relays that can be safely tapped onto other bits of kit with complete electrical isolation.

One other point - you might find the Stop and X2 modes a bit brutal for speed adjustments.  PHD only updates at the end of every guide exposure which could be several seconds apart, so you could end up hunting in RA swinging one side to the other.  If so, you could always synthesise an RA+ and RA- speed.  A simple variable mark/space oscillator switching the mount (for example) x2 to sidereal would enable you create an RA+ just a bit faster than sidereal, and similar a slightly slow RA-.  By varying the mark/space you can fine tune the RA+ and RA- that the ST4 sees.

Simon

ST4 fan out box.PDF