Simple usb autoguiding hardware

[samtheeagle]

Very nice lynol1000 Rather more professional than my effort! If only I new of this before I started work on my gizmo... Still, I've got it all finished and working now, and it's very satisfying to have crafted something from scratch

[lynol1000]

Sam, thanks for the kudo's! Which ASCOM scope driver base did you start with?

If anyone is a Mac/OSX type, PHD just added support for the unit

Pre-Release

Meade 909 clone: assembled and kit version, full specs, schematic, source

Gene

[samtheeagle]

The ASCOM support of .NET provides a Visual Studio template for a basic driver, so I developed from that... In C#.

[lynol1000]

Ok. I started with the 4.1 scope simulator as a base earlier last year, in VB6. It is for the Meade 909 clone that could use the FTDI USB-TTL232R serial cable as direct input. Darn cable cost near as much as the qty 10 price parts for this USB-ST4 one, even forgetting shipping. I do make heavy use of the cable though, comes in real handy with so many different PIC chips for direct input.

[samtheeagle]

I assume that you will have seen this already, but just in case... http://stargazerslounge.com/diy-astronomer/81238-simplegpusb-home-brew-auto-guider.html That's the write up I did for this little project, all the source code is included as well.

About the only marginally clever thing in the software driver is a simple queueing class for the pulse guide calls. Apparently if dual axis control is supported the PulseGuide() method must return immediately, so I had queue the requests up, and run separate threads to execute them sequentially. I'm fairly certain that the queue never has more than one guiding command in it at a time, but it's written to adhere to the interface specification...

[lynol1000]

Nice!

Did you implement the 'IsPulseGuiding' ? Lets the application poll till all guiding complete.

Any sign of ground loop issues without an isolated interface or is this the only connection to the scopes electronics?

There was quite a long thread end of May on sct-users (Yahoo egroup) on isolation requirements. The two chips I picked, one (ps2501-4 open collector) allows for only negative gnd systems and the photo fet's (TLP227A-2) are ground agnostic.

[samtheeagle]

Yes, I implemented the IsPulseGuiding() method. If the PulseGuider helper class is currently executing a guiding instruction then it returns true.

I couldn't honestly say I have a clue what you're on about with the other questions! I'm no electronic engineer... My initial intention was to use a quad opto-isolator as the switching chip, but I never got it to work. As I mention in my write up, there was a very important configuration setting on the USB->Serial interface board which was the actual cause of all my woes. So the opto-isolator circuit probably worked fine and was just scuppered by the other problem This is the one I was trying to use: Opto Transistor Isolator > Maplin

In the (sadly) very limited opportunity I have to use my guider it appears to have worked without a hitch, but that's not to say that it wont in the future? This device is the only thing tapping into the hand controller circuit, it uses the ShoeString modification to connect in.

Feel free to keep asking questions, just use small words

[lynol1000]

There are 3 basic type of isolated coupling (that do not cost an arm and a leg). The old tried and true mechanical relay, energize a coil and it causes contact closure. There is not a voltage reference for the contacts, current can pass in either direction. The modern version are back to back FET's whose gate it driven by a photo transistor excited by an internal LED, again current can pass in either direction. The open collector type, again LED exciting a photo transistor that drives the base of a single or darlington array, this one does have a unidirectional current flow, GND must be on one side and one side only.

The big thing is how much current you need to pump in to either the coil or LED to get the 'contacts' to close. With the solid state types there is a relationship to how 'bright' the LED is to how much current can flow through the 'contacts'. Many are very inefficient, 5-10ma in and the voltage across the contacts will only go so low based on how much current is flowing. 5ma in to LED, 5V @ 1ma across contacts and you get down to 0.5V across contacts, 10ma in to LED, it goes down to 0.25V across contacts. The tlp227a is quite efficient. With 3-5ma in to the LED you can switch 100ma@5V down to well less than <0.1V. This same 3-5ma in to the PS2501 can only take 10ma down to less than 0.1V(@ 5V). Try to feed it 50ma across the contacts and the voltage will be 2V+.

Now the current available to drive the LED's can come directly from the output pin of a chip (through a resistor in most cases) but the chip itself is only capable of supplying so much current out unless used to drive say a transistor that will then drive the LED.

In the USB-ST4 I did I use the PIC chip output through a 1k resistor for 5ma out to the LED then either the PS2501 or tlp227, which have exactly the same pinouts so either drop into the coupler socket.

USB to ST4 output guider

[Lord F]

Hi, i just want to say thanks for sharing this project, it works great! I used the opto coupler from maplin, it works as well as the darlington array. (i tried both)

Just a quick question if i may, i already have an st-4 guideport, and the fastest guidespeed my mount can do is only 1x sidereal rate. So i had a look at the driver.cs file in visual studio, could i just alter the degrees per second values in the axisrates function to fit?

[lynol1000]

Lord F,

I saw your post a while ago but not sure who it was addressed to?

A guess would be the firmware in your mount controls what rate is used when the ST4 inputs are asserted. Some firmware can be patched to change the rate (e.g. Meade) but I think you are using an EQ6? Does the EQ6 allow serial guide commands and is there a value for the guide rate? If there is it may also alter the rate used when ST4 is used.

Also, back in May Reggie commented on bluetooth, here's the latest gadget to pop out:

Bluetooth Telescope Serial Adater

Gene

[samtheeagle]

Hi Lord F, sorry I missed your post, I only just saw it now as lynol1000's response popped the thread back up on the new posts...

If I'm understanding your question correctly then yes, you should be able to tweak the code to use whatever guide speeds you want. As you have already figured out the bit you'll want to change is the AxisRates Then you might want to do some cosmetic stuff to change the 2X references to 1X etc, but the AxisRate value is the important bit that the guiding software uses to determine what command durations to issue.

Hope that helps Feel free to PM me if I don't respond promptly to other questions in the future!

Glad you like the project, it's good to know that it's of use to people

[Stub Mandrel]

Is the Ascom serial to ST4 protocol available without installing the entire framework?

Surely it can't be that complicated I need a 66Mb download to get hold of the four commands?

Edit: I should say that the link http://stargazerslounge.com/diy-astronomer/81238-simplegpusb-home-brew-auto-guider.htmlseems to be broken :-(

I've made my own RA drive, I want to add DEC as well and if I have two steppers under uP control it's an obvious step to put a couple of FTDI USB-serial chips* on it to give me autoguidiing and goto. The protocols for GoOTO were easy to get but the open-source ASCOM ones are eluding me!

Neil

*Actually do the protocols let you send GOTO and guiding data over the same link?

[Stub Mandrel]

Well, I downloaded the ASCO platform developer framework and it seems the only way to find the command set from it is to work it out backword from the source code.

The ASCOM email is broken - my email asking if there's a simple summmary bounced :-(

But...  iOptreon have guide:

https://ioptron.com/images/up/iOptron%20Mount%20RS-232%20Command%20language%202014%20V2.0.pdf

Unfortunately it's incomplete (it only covers mount commands), but at least that's all I need to start with. It is not well explained (for example guide rate is given as 'n.nn'  which can only be in the range 10 to 90 (0.10 to 0.90, I assume) but with no idea of units... ho hum!

Can anyone shed some light on this.