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Re: Onstep Operation

Frank Johns
 

Thanks for the pointers on 3D printing - should be interesting ;-))

regarding pull up resistors on on my Instein OnStep it seems that there are none in the OnStep circuit.
can they be incorporated into my simple hand controller? If so what, how many and where? Please bear with me as I am mechanical not electronic.


Re: Onstep Operation

Dave Schwartz
 

Pull-up resistors are used to raise ('pull up') the voltage level (which equates to the logic level) on a GPIO pin that is expected to be used in a normally high state like the ST4 control lines. When the external device is not requesting an axis movement, the microprocessor should see a consistently high logic level until the device actively grounds the control line to command a movement. The same thing applies for pull-down resistors when the active state is high but we'll ignore that since OnStep doesn't use that mode for user devices.

If there were no pull-up resistors at all, the line would be in what is called a 'floating' state where the voltage could be affected by a great variety of things such as stray electrical or magnetic fields. These fields can induce positive or negative voltages on the line (after all, the wire acts as an antenna too) which could be interpreted as random high or low logic levels causing chaos.

Most microprocessors have internal pullup resistors which can be enabled by the software. For OnStep, that is what the ST4_PULLUP option does. However, the internal pullup resistors are on the chip itself and are necessarily quite small and low power. The ones on the STM32 are in the range of 30k to 50k ohms. This is known as a weak pullup resistor (in this case, very weak). At 5V, a 40k resistor can only pass 125 microamps of current. This means that any transient on the line that induces a negative current of 125 microamps (which is quite easy to do) will overwhelm the internal resistor's capacity to supply current to keep that line held up. Thus the microprocessor will see an uncommanded movement and, again, chaos will ensue.

So we use external resistors to create a strong pullup. For the STM32, I use a 2.2Kohm device. As such, it can pass 2.2 milliamps of current at 5V and thus a transient on the line will have to be much more massive (~20x) to cause an erroneous reading. As a consequence, any device that uses these lines for signalling or communication will have to be able to sink 2.2ma to ground but this is not hard achieve either with switches (can usually sink way more than that) or electronics (microprocessors can usually sink at least 10ma on an appropriate pin).

About the 3D printing... I think that's going to be a good printer for you. It can be addictive though and you'll probably end up spending more on various filaments that you did on the printer (I have... now have 17 different spools lying around which are worth almost twice what the printer cost).

After a bit of a learning curve, I found that designing projects in FreeCAD was quite enjoyable. The most useful advice I have when designing a model with multiple parts (like my SHC case) is to start your model with the part with the largest footprint so that subsequent sketches added on for the later parts don't go into negative offsets or can't be made as additions to previous components. I made such a mistake in my first version and got into a state where there were errors that couldn't be resolved. Starting over from scratch after I had the complete build path in mind made it quite easy. Another FreeCAD tip is to keep all your dimensions in a FreeCAD spreadsheet page. Then its easy to reference a dimension in multiple places, there are no 'magic numbers' and if you change the value in the spreadsheet, the whole model immediately readjusts. I use around 50 dimensions held in a spreadsheet for my SHC case.

On 2019-02-17 6:23 a.m., Frank Johns via Groups.Io wrote:
Dave - senior moments ! I get them regularly.
can you explain the ‘external pull up resistor network’ - perhaps I need such.

you may be wondering what I’ve done about the STM32 kit I had off you (and the Hand Controller). Both are ready but cannot sort a suitable case for them and so have now acquired an Anet A8 3d printer kit in order to (hopefully) make them myself. Brain now under severe pressure - something else new to master!!


Re: Onstep Operation

Frank Johns
 

Dave - senior moments ! I get them regularly.
can you explain the ‘external pull up resistor network’ - perhaps I need such.

you may be wondering what I’ve done about the STM32 kit I had off you (and the Hand Controller). Both are ready but cannot sort a suitable case for them and so have now acquired an Anet A8 3d printer kit in order to (hopefully) make them myself. Brain now under severe pressure - something else new to master!!


Re: Onstep Operation

Dave Schwartz
 

I remember you told me that before - obviously I forgot (I claim 'Senior moment'). I don't know why incorrect information would be knowingly kept.

When I built a 'basic hand controller' for my STM32 project, that is pretty much all I did... pushbuttons that would connect pins 3, 4, 5 or 6 to the ground on pin 2. I didn't use that for very long before we had the ESP32 SHC working but we did find that it wouldn't connect without the external pullup resistor network even when the internal pullups of the STM32 were set to be used ith the ST4_PULLUP setting. Maybe that was just an STM32 thing and the ATMEGA 2560 in the Instein controller can use a handbox reliably without them - I just don't know.

On 2019-02-16 7:14 p.m., Frank Johns via Groups.Io wrote:
Khalid - my Hand Controller is a simple set of buttons connecting pins 3,4,5 & 6. Are you indicating that there should be some resistor in those circuits? If so what is required?

Dave - when I challenged Instein on the wiring he indicated that the diagram on his website is not correct (I have no idea why he keeps it there) - he said the pins 345&6 are for RA and Dec. Pins 1&2 are soldered together to ground


Re: Onstep Operation

Frank Johns
 

Khalid - my Hand Controller is a simple set of buttons connecting pins 3,4,5 & 6. Are you indicating that there should be some resistor in those circuits? If so what is required?

Dave - when I challenged Instein on the wiring he indicated that the diagram on his website is not correct (I have no idea why he keeps it there) - he said the pins 345&6 are for RA and Dec. Pins 1&2 are soldered together to ground


Re: Onstep Operation

Dave Schwartz
 

Looking at the Instein.eu site, I don't see anything that could be pullup resistors in the picture of the PCB.

It also shows the ST4 pinout (snip attached) which is not compatible with anything I know of.

On 2019-02-16 6:04 p.m., Frank Johns via Groups.Io wrote:
I checked the ST4 settings and it is ST4_PULLUP

Tonight I tried it with the ST4 plug in and a few minutes after doing a Sync after the align, Onstep stopped tracking.

I then restarted and tried it with the plug out and after Sync the star was held for just over 15 minutes when the clouds came over and I had to stop, although I could see the RA motor turning.

Both motors cold to touch.

The conclusion is some conflict with the ST4??

On another point - I find the control boxes on the GOTO page quite small, especially when at the eyepiece. Is there a way to make then larger, or perhaps use the page which comes up when pressing the Guide/Focus button?

.


Re: Conversion of LX200 Classic

 

This is amazing stuff - very much along the lines of what I plan to do.   Question:   Are encoders required for these builds?

Thanks

Tom


Re: Onstep Operation

Khalid Baheyeldin
 

On Sat, Feb 16, 2019 at 06:04 PM, Frank Johns wrote:
The conclusion is some conflict with the ST4??
Do you have a network resistor soldered inside the controller on the ST4 lines?


Re: Onstep Operation

Frank Johns
 

I checked the ST4 settings and it is ST4_PULLUP

Tonight I tried it with the ST4 plug in and a few minutes after doing a Sync after the align, Onstep stopped tracking.

I then restarted and tried it with the plug out and after Sync the star was held for just over 15 minutes when the clouds came over and I had to stop, although I could see the RA motor turning.

Both motors cold to touch.

The conclusion is some conflict with the ST4??

On another point - I find the control boxes on the GOTO page quite small, especially when at the eyepiece. Is there a way to make then larger, or perhaps use the page which comes up when pressing the Guide/Focus button?

.


Re: Showcase: Built With OnStep

Dave Schwartz
 

For the people who I've been sending OnStep ESP32S SHC's to, I've got an update to the 3D-printable button cap for the 5-way switch.

I am planning to experiment with 3D-printing a harmonic drive reducer and the material recommended for the flex spline is 'Soft PLA'. This stuff is sort of mid-way between regular PLA (completely stiff) and TPU (really rubbery). I had planned to make the 5-way cap with TPU but it was a failure because my printer (Anycubic i3 Mega) couldn't feed it properly. Although the vendor has an upgraded extruder drive that theoretically supports TPU (now called the Anycubic Mega-S), I decided to retry the 5-way cap in the soft PLA even after installing the upgrade.

The result is that it worked really well. I found I had to lower the extrusion temp even a bit below recommended (my hotend always seemed to run a bit above what was indicated anyway), turn off the heated print bed and set the travel speed to 20mm/sec (reduced even further to 75% with a setting in the printer AND use an external fan. It was a thing of beauty.

However, in making the design even better, I tweaked the FreeCAD design so that the button is 2mm taller (much easier to feel and push around) and tightened up the fit of the switchpost pocket since it now prints even more accurately than the orignal PLA design (although that may be due to the upgraded extruder drive).

The new STL file and FreeCAD source are in the same place as the earlier files.


Re: TeenAstro an Onstep device

Gilles Gagnon
 

Bonjour Charles,

I was on the road, the reason why my late reply. :-)

Superbe! I should post better pictures and a video or two of my AP400 modifications.

What was the material used for the housing? I assume ABS but there may be better 3D printer material for motor housings.


Re: TeenAstro an Onstep device

Charles Lemaire <Charles_Lemaire@...>
 

I am not the inventor Stephan is the maker!
http://www.astrobin.com/users/Sonixx/

The design is indeed very good, and use all the advantage of 3D printing.

Charles


Re: TeenAstro an Onstep device

Peter Dulowsky <peter.dulowsky@...>
 

Would love to have something like that for EQ5. Very good job Charles.


Re: Motorizing Vixen Porta Mount II

Charles Lemaire <Charles_Lemaire@...>
 

Hi Pete,

This is a great modification of the Vixen Porta! I love it.
I will buy a Vixen porta mount and prepare a motor kit :)

Thanks for sharing 

Charles


Re: tcm 2130 v 1.1 ?

Alin Tolea
 

Let me get them and see if they're coming with tape, you're my saviour once more :)

Alin

On Sat, Feb 16, 2019 at 12:32 PM George Cushing <pinyachta@...> wrote:
Alin, let me know if you need some tape I have a roll.



--
Alin Tolea, Ph.D.


Systems Engineer, Omitron Inc.

cell (202)-550-2401
office phone: (301)-474-1700 x 624
office fax: (301)-345-4594




Re: tcm 2130 v 1.1 ?

George Cushing
 

Alin, let me know if you need some tape I have a roll.


Re: TeenAstro an Onstep device

John Scherer
 

Love those covers Charles.  I need to figure something like that out for my G11!


Re: Minipcb 2 pcbs available.

John Scherer
 

minipcb 2s”.  Email me the shipping address 


Re: TeenAstro an Onstep device

Charles Lemaire <Charles_Lemaire@...>
 

Maybe here you can better see how it is made...


in the field:

in the field:


Re: OnStep Software Development

Howard Dutton
 

The Alpha OnStep's Smart Hand Controller code now has:

An OnStep logo on the splash screen.
All user settings in a single Config.h file.

Under the hood some obsolete (and inactive for us) TeenAstro related code was removed.