That's what ST4 autoguiding is. It sends corrections to your mount by emulating the button depress.
It should be quite straightforward depending on your model.
you might have to do some soldering to wire it to an RJ11/45 connector so the guide camera can connect to it. but once its done, it should work well.
if you don't have a guide camera with an ST4 port, you can get the shoestring astronomy webcam adaptors that provide an ST4 interface.
are you able to solder/understand/test simple circuits?
Please post some info about your mount with pics of your hand controller
ok, that's completely different from the eq3 hand controllers in terms of what can be done.
can you confirm if the speed controller dial is a simple pot?
What comes to mind is a simple microcontroller based approach that can either increase or decrease the resistance value of the pot based on the ST4 pulse. I've built a similar unit to interpret the ST4 pulses.
The ST4 commands are RA+, RA-, Dec+, Dec-. meaning speed up RA, slow down RA, same with Dec.
since what you have is a speed controller, you can do the same thing.
it goes like this. the ST4 port of a guidecamera or USB-ST4 has 4 pins that are normally held high (+5v). This is after an opto-coupler, so its safe. It is controlled via the Phd autoguiding software ( you set mount type to "on-camera").
So when the guide star drifts east, it pulls down the RA- pin asking the mount to slow down, or the RA+ pin if it drifts west asking it to speed up.
Phd determines the length of the pulse based on its calibration.
you then connect the 4 pins to an MCU (I use picaxe as its very simple to use). The MCU will then monitor the state of the 4 inputs. when a pin goes low, it either raises or lowers an output, your choice, and this can then trigger an opto-coupler that switches a fixed or variable resistor that is across each side of the potentiometer's centre tap or in series to the centre tap. or you could use a digital potentiometer.
you'll have to experiment for the actual resistance value or you could measure the effective resistance after turning your knob by your normal amount and then calculate.
The idea is rather than you rotating the dial, which just varies the resistance, you add or remove a resistor that's either in-line or in parallel to the pot.
Although it sounds complicated, you should be able to assemble this in on a general purpose board and the whole thing should cost you under $30.
if using picaxe, I'd recommend the 20M2 as it has sufficient input and output pins. opto-couplers are only a few dollars each.
i'll see if i can draw up a circuit. I have already written the code for the ST4 interface for the picaxe, so let me know if you need that.
Cheers
Last edited by alistairsam; 10-01-2013 at 12:22 PM.
yes, as long as your polar alignment is good, you can get away with no Dec guiding.
btw, you need to turn off Dec guiding in phd and you'll need to monitor only the two RA pins.
what guide camera do you have?
you can use phd to drift align by disabling the guide outputs and monitoring drift after each adjustment.
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,472
Petr,
I remember those old monsters! Our school bought one for the astronomy club. Memories!
This is probably a very old style of device that uses a timer chip like a 555. The combination of a fixed capacitor and the potentiometer resistance governs the timer speed which is adjusted for siderial (or other speeds) The push buttons either add in or subtract resistance to the timing circuit making the motor speed up or slow down.
Auto guiders as already noted are voltage switching devices. They won't switch resistors. You can do it but you'd have to add some sort of intermediate relay, that switches in those high/low resistors. Simplest low tech method is probably an old fashioned solenoid type relay that physically opens and closes mechanical switches that replace the push buttons or if you want to retain some manual control, hook them up in parallel after verifying the circuit is as I describe of course.
Sounds like an old Sampson Mount. Twenty years ago they were considered top but even the cheapest of the modern mounts will perform better. I think trying to computerise it will be a very frustrating exersize, even if you have access to machinery and are adept with electronics.
The "anolog" control device will need extensive design work to make it work with the output of an auto guider. Do you have a worm and worm wheel drive on both axes. If so can you fit stepper motors to the drives. If so you could use a control system like the Bartell's system.
Twenty years ago I tried to build a mount like that but fitting drives was such a problem even when I have all the necesary machines and tools was so frustrating. I had designed and built a "goto" stepper motor drive system that worked but never got it fitted to the mount. I eventually gave it up and bought a LX200.
Auto guiders as already noted are voltage switching devices. They won't switch resistors. You can do it but you'd have to add some sort of intermediate relay, that switches in those high/low resistors. Simplest low tech method is probably an old fashioned solenoid type relay that physically opens and closes mechanical switches that replace the push buttons or if you want to retain some manual control, hook them up in parallel after verifying the circuit is as I describe of course.
Joe
I'd strongly advise against solenoids, not really required.
Hence my suggestion to use opto couplers as a digital switch. Easy and cost effective.
Replacing the motors with steppers would be good but very expensive as the appropriate gearheads for steppers are not that cheap. I've been down that road. Then you have the problem of an accurate controller for the stepper. I'd say that's a lot more complex.
