SPC900 LXmod yesyes style ;-)

[Reggie]

oh nice, that should be fairly simple to implement I guess it depends how much money/time you have as to whether making something for yourself turns out cheap I've been looking around on ebay and found these little boards. I've got 12v versions of those steppers and they're fantastic little units @ 4096 steps per revolution due to the gearing, might be worth a look at for your filter wheel? Might even be able to put them on your X/Y rig, I expect hunting for guidestars on the spc900nc could be made easier if you didn't have to touch the scope at all? Could be very neat making the camera do a spiral search for guide stars

Yesyes, I might have a go at doing your mod today, Iv'e got an spc900nc and 2x880s to mess about with, I won't be doing the full usb hub mod as I don't have one.

Just looking at your mod page and it's not entirely clear where all the connections go on your board, looks like some component legs share a hole but can't be sure exactly which, any chance you could put up a board layout to go with the pictures? I used DIY layout creator last night to knock up a quick stripboard copy of your schematic, mine comes out a bit larger than yours but might be freindlier for those not used to soldering? I've also knocked up a single sided board and schematic in eagle if anyone is interested in etching their own boards?

[DIYASTRO]

Hi Reggie,

Those little boards do look nice! must find time to scan the ebay site you mention a little bit more, some interesting stuff! The big problem at present is trying to get the current / power consumption for the circuit which is the camera, 4 way usb hub, serial/usb converter and the additional circuit for LX amp off. The USB will only deliver 500mA so need to be carefull not to overload it.

Regards

Boyd

[Gina]

Powered USB hub? Or maybe provide your own beefier 5v supply.

[DIYASTRO]

Gina,

Problem with powered usb hub or seperate supply is the extra cables. The real beauty of the Yes Yes mod is the single usb and since I intend to do my PHD guiding with netbook USB ports are few.

However, it may well be that you are right and a seperate supply would be usefull, I have thought about it since a seperate power supply would allow for a 12V fan with greater cooling capacity and a programmable stepper motor driver for the filter wheel.

I also want to keep the whole unit as small as poss and not too heavy.

hope your obsy project gets finished soon

Regards

Boyd

[Reggie]

the powered usb hub is still limited to 500ma as I understand things, or will it actually provide 500ma per port? I guess it depends on the current draw for the webcam, the serial adapter (at least for ftdi) will only ask for 90ma and will be in the low ma for actual consumption, as for the lx mod, the original mods took power from the webcam itself, so it really should come down to webcam and serial adapter power usage.

Adding various voltages for various doohickys is relatively simple and cheap too, you can use a 'low dropout' regulator such as a micrel MIC29152, which are about £2 each from ebay and will give you 1.5a output. or you can go for their beefier versions that do 3a and 5a too, they do fixed versions too and just feed it off a 12v battery, of course you could even supply power to the usb hub from something like that too, which would help the laptop battery life.

[yesyes]

Yes, a powered USB hub does (or should) provide 500mA per port, up to the max current that the power supply can deliver, of course.

The downside is, as Boyd has already mentioned, that you still need another cable in addition to the USB cable, which kind of defeats the purpose of this way of doing the mod.

I'll measure the current that the "yesyes modded" webcam draws and report back. I should be able to do this tonight or tomorrow latest.

[yesyes]

Yesyes, I might have a go at doing your mod today, Iv'e got an spc900nc and 2x880s to mess about with, I won't be doing the full usb hub mod as I don't have one.

Just looking at your mod page and it's not entirely clear where all the connections go on your board, looks like some component legs share a hole but can't be sure exactly which, any chance you could put up a board layout to go with the pictures? I used DIY layout creator last night to knock up a quick stripboard copy of your schematic, mine comes out a bit larger than yours but might be freindlier for those not used to soldering? I've also knocked up a single sided board and schematic in eagle if anyone is interested in etching their own boards?

I see. I assumed everyone would work their way through the strip board layout. The one I made is as small as I could get it as I didn't want it to be larger than the USB hub PCB. There is indeed one hole where 2 pins go in to save some space. There is also some unusual transistor pin bending going on.

I will try to make a board layout. That DIY Layout Creator looks quite good for that. Let's hope it supports UTPB (unusual transistor pin bending)

[Reggie]

Ok, hub first, the reason I ask about power is that I had assumed that it would be 500ma per port but I had issues in the past, any idea what the IC is on your hub? I'd much rather have an extra cable going to the unit than have an unstable setup, especially if that non-powered hub is also sharing with the other usb socket in it's 'pair' on the motherboard.

As for the stripboard layout, the schematic is fine but as you can't see a lot of connections it's not clear from the pictures what is going where With the layout I did, it only comes out at 11x10 wuth a bit of extra judicious placement I could probably lose 1x1 from that, maybe 2x2 if I move the cut points, so it's still less than 1" square.

with regard to your cabling comment, I am totally with you on the amount of cabling going on, it's starting to get a bit silly, I'm wondering whether it would be prudent to leave 2 of the cables attached to the hub to allow yourselves to plug in extra devices, such as focusers, heaters etc? It seems that everything is running via USB these days, on 2m or less cables, so you end up either running extenstions for each device, which starts to get to the limits of usb cable length at 5m, or a 4port/7port usb hub on th eend of an extension.

[yesyes]

OK, I've tried to make that strip board layout (attached). Could you have a look see if this is clear now, please. If so, I'll add it to the articles on my website.

As for the hub, the one I'm using doesn't do any power management at all. The 5V from the USB input is routed directly to the outputs. So in this case all devices together are limited to 500mA. I guess that is within specs for a hub that doesn't have any provision for external power.

On this photo you can just about make out the writing on the USB hub chip:

https://picasaweb.google.com/117034922665750406576/201110SPC900LXmod#5666706195272688914

I've tried to find this chip as a separate part but with no luck. There was a moment when I thought about putting everything on a single PCB (hub, serial adapter and LX circuit) that would just plug between the 2 boards of the SPC 900. But I dropped that idea. Too much hassle and it would actually turn out more expensive than building it the way I did.

[Reggie]

Hi Chris, that's great, much easier to understand what's going on.

with regard to the hub, that is my main issue, there are oodles of bits and bobs that want usb, and they all require some kind of power, so if I go a hub in a box route, I'd like to utilise all 4 ports. more investigation on the hub/power part is needed. At the moment I'm currently looking at the following usb connections:

eqmod

qhy5

dslr

focuser (maybe 2)

spc900nc (2 ports)

dew heater

that's 5,6 or 7 usb ports needed depending on the configuration.

It's starting to get silly, especially as my laptop only has 3 ports :/

eqmod, dslr, focuser, 1 of the spc ports and the dew heater are all on usb to serial adapters, I wonder if there's a 4port usb to serial adapter out there, I know there's a 2x serial to usb adapter.

*edit* turns out there is a 4 port usb to serial adapter at £17, I think I'll get everything up and running first, see what I need to deal with, only got 1 focuser working atm, dew heater isn't made and still waiting for resistors for the spc900nc mod

Cya,

Reggie.

[DIYASTRO]

Where do you find the 4port USB serial adapter (£17) Reggie?

Chris,

It would be great if you could get that current consuption figure for your camera mod.

Nice to know we have aggreement that it would be a shame to have to resort to more cableing when your wounderfully simple yet elegant solution to one USB cable is working out so well.

Currently working on another Yes Yes mod with built in filter wheel which I am determined to get working without using external power supplies if poss.!

Boyd

[yesyes]

Boyd, I will have to do this tomorrow. When I wanted to add the board layout (posted above) to the article on my website quickly, the website crashed.

Got it working again now but that scared the hot place out of me. (note to self: MAKE BACKUPS)

Not in the mood for soldering and also got a few other things to do...

But will do it tomorrow. ;-)

[Reggie]

Boyd, it was £17.99 on ebay

I've just had a look around chris's site, some very nice mods on there indeed. Unfortunately right now I'm going to have to settle for what's at hand, maybe I'll get round to building a decent multi/variable voltage bench supply.

[yesyes]

Excellent find Reggie. I think I'll have to get myself one of those...

I wonder if all the curcuitry is in that small box in the middle or if that's just a USB hub with serial converters in each DB9 plug.

And thank for looking round my website. I'm always glad to hear that some of the info there might be useful for someone. Makes it worth doing... ;-)

[yesyes]

Reggie, regarding the USB hub, I would recommend getting a good quality powered USB hub and a beefy 5V power supply for it. Have a look at my Power and Data Box

That has 2 7-port USB hubs powered by a 5V 5A voltage regulator which in turn is powered by a 12V 20A power supply. You could get a separate 5V power supply and use that for the hub. That should be enough for all the things you listed I guess.

Most of the things need very little power, such as the USB to serial converters. The QHY5 and the webcams probably take the most (the QHY5 is USB powered, isn't it?). The DSLR has it's own power supply so only needs very little USB power for communication. For the focuser(s) and dew heater it depends on whether they get their power from the USB. I doubt the dew heater does?

[Reggie]

Oh sure, I appreciate that the ftdi range of serial adapters will require 20ma etc. per pin, it's really dependent on how much the underlying device requests, if that adds up to > 500ma then I'm stuffed. A powered 7port hub seems the way forward.

The focuser will get some power for the microcontroller(s) from USB but the stepper will be supplied seperately. The dew heater may or may not get power for the microcontroller from usb, I really haven't decided, the dew heater in theory will be automatic, so serial is really only for logging as it might allow for profiling of settings. I haven't decided entirely what I want to do yet

[yesyes]

Chris,

It would be great if you could get that current consuption figure for your camera mod.

Good news!

Just finished my (crude) measurements. I took a USB plug and a USB socket, connected 3 wires straight through and soldered 2 separate wires to both Ground pins. Then I put an amp meter in series with the ground. Then I used that rig to connect one of my LX modded SPC880 to USB.

here are the measurements:

160mA - plugged in but not showing video

190mA - showing normal video 640x480 @ 5fps

210mA - taking 10 sec LX exposures in SharpCap 640x480

220mA - showing normal video 640x480 @ 15fps

230mA - showing normal video 640x480 @ 25fps

240mA - showing normal video 640x480 @ 30fps or 60fps

The highest current draw I was able to measure trying various combinations of settings was 240mA. So there is still 260mA left for other things. And you might not always need all of the devices at the same time...

[DIYASTRO]

Cris,

BRILLIANT! Best news I have had for days! Nice to see the peak at 240mA regardless of doubling frame rate from 30 to 60fps.

the 'spare' 200mA ( since I would not like to push the limit) should drive my filter wheel with care. It will need good bearings and have to be well ballanced though so as not to strain the motor but on the whole very possible. THANKYOU

Boyd

[Reggie]

Well done on measuring the current draw Chris Another thought might be on the USB bandwidth too? I'm deviating from your design slightly here but if we use all 4 ports on the hub, a usb 2 hub going into a single USB 2 socket will still only have 480Mbits of bandwidth.

Another question while we're on LX mods, they use rts and dtr for the signal lines, are there any other pins we could 'hijack' that are usable in phd/sharpcap? Just thinking a 3rd pin would be mighty useful to do away with/compliment the physical switch to turn the LX mod on/off?

On a slightly side note, I have a dual port usb to rs232 dongle here, I took it apart last night to see what it was up to, the chip itself is a moschip 7720 which is TTL levels. Unfortunately, it's also got 2 RS232 to TTL level converters which put the IO voltage somewhere around the 10-11V point

So if anyone is thinking about using a 2/4port usb to serial adapter, ask the seller to confirm voltage levels. Of course I could use max232 chips to re-convert the levels back to TTL but it seems excessive, I might see if it's viable to remove the onboard converter chips, although the usb to serial chip is a small qfp package by the looks of it, so not particularly easy to tap all the necessary wires to.

[yesyes]

regarding bandwidth. as far as I know the SPC900 registers as a USB2.0 device (you do get the "this device could perform faster..." message when you use a USB1.1 hub) but it only uses USB1.1 speeds (12Mbit/s). So there should be plenty bandwidth left for other stuff. I would worry only if you are also using another USB2.0 full speed device. The bandwidth needed by the serial adapter is virtually zero, especially as we are not even using any serial data but only the handshake lines.

Funny you should mention the extra pin/line. I did ask Robin (the SharpCap developer) that exact same question for the exact same reason here. It might be possible but not really required. He said we could use the AmpOff line (DTR). That seems to get activated when you select the LX mode cam. So it could be used to enable AmpOff as well as switch the cam to LX mode.

However, I found out that the switch might not be necessary at all. If I use a modded cam with the switch in LX mode (open), then it behaves perfectly normal in any software that uses the cam (e.g. Skype). When I switch to LX mode in SharpCap (not changing the switch on the cam), it does long exposures. So at the moment it looks like the switch is not needed and can be left open. Would be good if you could confirm that with your cam.

The serial adapters I currently use are RS232 levels, not TTL levels. That's not a problem for the transistor based LX circuit. That's what the diodes are for, to block the negative voltage. It is a bit silly to convert TTL levels to RS232 levels only to use them as TTL signal levels again. But that's how most USB to serial adapters come. And they are so cheap that it's not worth it building your own with TTL levels.

[Reggie]

I'd forgotten that the spc cameras only run 12Mbit Definitely wasn't planning on reconverting the rs232 back down to ttl, it is a bit daft to say the least but if you're not experienced with soldering to small pitch stuff it may be your only way to convert back down to ttl, I just thought it was worth mentioning, I wouldn't want someone to buy an rs232 usb to serial adapter, expecting TTL @ 5v and then frying an arduino, or having to buy extra components to fix the levels

As for the extra pin/line, I have another reason for asking, I have some bluetooth to serial boards here but as standard, rts/dtr don't work, but they can be switched on using the mfrs tools, or at least rts can, so if I may only have 1 trigger line from the bluetooth adapter.

I also seem to recall something about when the camera is in 5fps mode then you didn't need the switch but it's been a while since I messed with any of this.

I'm still waiting for my resistors to turn up.

I did wonder about the transistor circuit, if everything was actually necessary or not in there? I thought the diodes might've been for reverse connection protection and thought as we're only switching 5v on/off and the serial adapters I use are either 3.3v or 5v that the amp off transistor would only be necessary for switching q3 through the zener diode?

I couldn't find 2n4148 diodes but I do have a bunch of 1n4148s and I also didn't have BC547 transistors, I subbed those out for 2n3904s (both pnp, broadly similar). I think that should be ok?

Reggie.

[RogerTheDodger]

BC547 is NPN.

[yesyes]

argh... my schematic says 2N4148 but it should of course be 1N4148. I will have to correct that. Also, any NPN transistor should do.

If you had TTL level serial, you wouldn't need the diodes in-line with RTS and DTR. They are only needed if you use real RS232 levels that have negative voltages.

However, I'm still not sure what the function of that zener diode is. Do you happen to know?

I would also have a few questions about those Bluetooth modules (I ordered some for a different non-astro project) but don't want to go too off topic here.

[Gina]

Chris, do I gather that you have managed to separate out the LX frame? Last I remember, there was a problem.

[Reggie]

hehehe, I'm glad it was a typo, even though I did spend 20mins on google trying to find 2n4148s!!

I think the zener is to lower the actual voltage from q3, iirc the zener is supposed to be an 11v zener, I don't think the amp off mod is truly off, it's just reduced by the zener.

as for the bluetooth, pm me or start a new thread My thoughts are to get it working for long exposure and do away with any extra hubs etc. would just be the lx and amp off circuit + a bluetooth module.