Standalone LX webcam with PHD guiding- NOT!

[theodore]

Hi,

I had already completed my standalone long exposure philips SPC900 project when I saw this post :

http://stargazerslounge.com/diy-astronomer/132517-lx-control-signal.html?highlight=webcam+signal

So NOW I know it can't be done easily becuase you get a load of lost frames - I had tried to control the LX signal with a 555 timer.... didn't work!

I don't have a serial or parallel port and now I need to control the LX from PHD guiding. Does anyone know if there is a cheap USB>parallel cable available to do this? I don't want to fork out for a Shoestring or astronomizer one! There doesn't seem to be any guide on how PHD actually controls the webcam even though it has the menu option.

Thanks for any help,

Theo

[RogerTheDodger]

Why not just use the usb-serial cable mod, that works ok.

[theodore]

Is that a USB>serial cable? Where can I find details of that mod?

Also - I just carked the cam - cracked off a surface component and now its dead

Will start again if I can get another SPC900.....

Thanks anyway,

Theo

[theodore]

Quick thought - anyone tried changing the crystal oscillator in a webcam to 'trick' it into longer exposures?

Theo

[RogerTheDodger]

Try this thread for starters, there are a couple more on the same subject but that'll start to get confusing http://stargazerslounge.com/diy-astronomer/134194-webcam-mod-wiring.html

The interesting bit is from around post #22 it eventually all works ok, and is not as hard as it looks...

[theodore]

Ok, thanks Roger. I think I get it now - I need a USB>serial cable and to make the transistor circuit.

So this works in SharpCap, does it work in PHD guiding is the question I can't fidn any answers to??

Thanks,

Theo

[RogerTheDodger]

Yep, tried it in PHD the other night and it works fine.

[theodore]

That's great, thanks.

Also...managed to fix my SPC900 - switched the trashed surface transistor with one off a junk circuit and amazingly it lives!

[Gina]

Great! Well done.

[theodore]

BTW, tried swapping for lower MHz crystals in a couple of other webcams and it didn't work.

[Gina]

I don't know for sure but it's likely that the crystal determines the timing for the USB. So changing the crystal frequency might stop the USB working.

[yesyes]

I agree with Gina. It's most likely even worse than that. It probably determines the clocking for the whole processor inside the webcam. I wouldn't touch that.

Besides, even if it would work, you would have to slow it down massively in order to get any decent long exposure times. And you would still be stuck with a few fixed exposure times, just longer than the original ones...

[theodore]

Hi,

it was only an experiment with the crystal - It worked once before for me - to get a different range on a digital frequency meter, but that was a much simpler gizmo. You are right - changing the crystal stopped the USB working. At least now we know!

Theo

[themos]

Can't you recreate the LX signal with an Arduino MiniPro and an FTDI cable? I forget what voltage you need for the LX signal...

[RogerTheDodger]

It doesn't have to be an LX modded webcam for PHD, it will just stack the images itself from a standard webcam and use that instead.

[theodore]

I'm going to use it for guiding (to use fainter stars), not imaging, so I don't think stacking is an option.

I have it sorted now - going to use the serial 3 transistor method on the other post. Just waiting for the bits to arrive from Maplin, then I shall place them all in a sealed jar and wait three billion years for them to arrange themselves into a working mod.

Theo

[RogerTheDodger]

You mis-understand, the PHD guiding software if used with a bog-standard webcam will automatically stack the images, so if you select a 1 second loop it will stack the images over that 1 second and use that. If you do have an LX webcam, it doesn't need to do the stacking bit, it just selects a 1 second image from the cam. I have tried it both ways with equal success so far.

[theodore]

Didn't know PHD did that, when I use it with an unmodded cam, the loop time doesn't make the image any brighter. But I only ever use it on 1-2 secs. I'll have a closer look next time.

[RogerTheDodger]

Yeah, I didn't know until I read the post second from bottom here CN FORUMS ARCHIVE Telescope Reviews: PHD Guiding problem that was written by author of PHD.