an old hand controller

Questions about hardware and software not obtained from Shoestring Astronomy, but related to our products
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mhamburg
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an old hand controller

Post by mhamburg » Mon Oct 15, 2007 8:00 am

:?: I have an old Meade Research Grade dual-axis drive controller with a joystick. Is it possible to modify it for autoguiding using the GPKIT-EQ?

dpanderson
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Post by dpanderson » Mon Oct 15, 2007 12:07 pm

I don't know the specifics of this particular hand controller, but in general, most hand controllers that have four-button movement capability can likely be modified worst case by adding relays in parallel with the switches. This document:
http://store.shoestringastronomy.com/do ... idance.pdf
provides additional information.
Doug Anderson
Shoestring Astronomy
http://www.ShoestringAstronomy.com

mhamburg
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help in electronics

Post by mhamburg » Tue Oct 16, 2007 11:12 am

Thanks for the answer, Doug. I looked at the schematics but really have no experience in wiring these units. Any suggestions would be most appreciated.

Michael Hamburg :?: :?:

dpanderson
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Post by dpanderson » Tue Oct 16, 2007 12:34 pm

Perhaps you have a friend, coworker, or astronomy club member that would be more comfortable doing this kind of work.
Doug Anderson
Shoestring Astronomy
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mhamburg
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electronics wizard

Post by mhamburg » Tue Oct 16, 2007 8:45 pm

Thanks for the reply, Doug. If only I had!

Michael Hamburg :cry:

Brisley
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Old Meade Controller

Post by Brisley » Sun Oct 21, 2007 1:12 am

I have the same controller and I am also looking to make it operate with a relay driven interface.
Here are some tech specs:
There is a joytick with 2 pots (one has an offset control available to the user, the other one is present, but not available to user) and a small circuit board in the hand controlt.

12v/gnd to handset, 2 returns, 555 circuit on board in handset. 7474 on main circuit board, total of 4 either tip30/31 transistors on main board, with a pair of tip30's in the output circuit to the transformer that are mounted to the case for heat.
The Dec appears to be a simple case of taking the +12v (On ac, it is about 16.8v or so, on battery it will be direct battery voltage) on one side of a pot, the grnd on the other, with a center output running about 8.6 when centered, 10.8 when going North, 6.2 for south. They are then evidently comparing the voltage offset from center voltage and amplifying that up to 12v+- range.
The pot measurements were in the 1.6k range +- 200k.

RA is using the 555 circuit, with the pot getting 12v going through a 27 ohm resistor on one of the outside legs of the pot, the center leg coming back to the trigger/threshold circuits and a 5.6kohm resistor crossing between the legs of the pot.
There is a 10uf 25v cap from gnd to the center leg lead.
The pot when disconnected was giving a centered reading of 1300 ohms, with a low reading of 600 and a high reading of 1900. There is an offset control that actually allowed the pot center range to be shifted +-200 ohms with corresponding shifts on the high/low settings. This is used for fine manual speed control.

Not being an EE, I can look at circuits and build them from plans and expand them when I understand them, but I can't explain exactly what mode and timing is happening with the 555.

What I need is some help understanding what I need to build in the way of a control to effectively mimic the pots being thrown fully in any of the directions. It would also be nice to possibly be able to adjust the amount of the offset, as one may not want full speed for guiding.

Brian

dpanderson
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Post by dpanderson » Mon Oct 22, 2007 7:45 am

This might be hard to assist with, unless you have a schematic diagram you could send me.
Doug Anderson
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Brisley
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Old Meade Controller

Post by Brisley » Mon Oct 22, 2007 9:07 am

What do you need? Just the hand controller circuit or the whole thing?
I can lay out the hand controller to some extent. (Remember, I am not an EE :) so I could get some symbols off. ) I hand did a rough one so I would know where everything went in case a wire came off.

Basically with the Dec, I would think either adding in +12v (maybe through a pot for speed control and gnd (hooked up through pot so I can set how low to go) would suffice as we are wanting to control the voltage without interrupting it.

What I don't know is how to properly play with the 555, as we appear to be changing the frequency by changing the resistance.
Don't know if it would be proper to 'interrupt' the resistance by adding some more resistance in serially, which would cause a momentary break when switching, and if hooking up a parallel resistance load for the other direction that could be switched in when we wanted to lower the resistance.

Brian

dpanderson
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Post by dpanderson » Mon Oct 22, 2007 10:42 am

Just the hand controller would be fine.
Doug Anderson
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mhamburg
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Post by mhamburg » Mon Oct 22, 2007 8:34 pm

:roll: Amazing! I've just read your posts and replies and I am very certain I am in deep waters. Please keep me in your loop and throw me a lifeline. Thanks.
Michael Hamburg

Brisley
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Old Meade Controller

Post by Brisley » Sat Oct 27, 2007 12:21 am

Ok, I mapped the schematic. The Dec side is straightforward. There is a pot on the joystick, with Ground on one side, +12v on the other, return from center. The pot reads about 1k ohm when centered, with about a+-300 ohm shift for each direction.

The RA uses a standard 555 Astable Oscillator circuit.
These can be found on
http://home.cogeco.ca/~rpaisley4/LM555.html#2

Go down to the Astable Oscillator circuit. C1 is 10 microfarad, R1 is 270, R2 is a bit more interesting. There is a 5.6k ohm resistor in parallel with the pot. The pot reads about 1.2k with about a +-400 ohm shift. This gives about 1k ohm, which if you plug in these values and use about 1060 for R2, you get about a 60hz value. (Pins 4/5 use the standard setup, visible higher up on the site, with C2 as a 4.7 uf 25v.)

Now I can see dec controls adding in some resistance tied either to 12v or ground, depending on direction. This could be done with a pot for speed adjustment, with the relays controlling whether to add in ground or +12v.

What do we need to do for RA? I am not good at figuring the resistance values when paralleling. Also, do we need to be concerned about breaking the value to add in resistance in series? We need to keep the pot in the circuit, as it does the fine tuning of the RA speed.

Is this enough info?

I have my hand schematic, but don't know how to get it up here.

Brian

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Post by dpanderson » Sat Oct 27, 2007 7:55 am

If you have access to a scanner, you could scan them and send to us via email. I could probably reconstruct it from your description, but getting your scanned hand-drawn schematic would be much better.
Doug Anderson
Shoestring Astronomy
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mhamburg
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an old controller

Post by mhamburg » Sat Oct 27, 2007 11:31 am

:roll: I am truly impressed at the progress you are making. How am I ever to make sense out of it?

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