USB hubs, Cables & RS232

[RyanParle]

Over the past few years the number of nights where i have been able to image successfully have been rather low, usually there is some technical gremlin that prevents me from getting my rig up and running.

Most of the issues seem to be hardware related, with flaky connections between the computer and the various bits of telescope hardware usually troublesome USB to RS232 adaptors & USB hubs, So i have decided to sort out my connectivity issues for once and for all.

My laptop has 4 USB ports which are configured as 2 USB controllers each with a 2 port internal hub, It also has a single PCMCIA slot.

The devices I need to connect are:

Telescope mount : USB

Canon 10d : USB & RS232

Guide Cam: USB

Focus controller : RS232

PS2 style game pad : 1x USB (the game pad is for mount control via EQASCOM)

Bluetooth interface : PCMCIA (used for GPS)

The 10d needs its own direct USB connection to the laptop as the large amount of data chokes the connection if a USB hub is used, the remainder of the USB connections can go via a hub if needed.

Option 1:

buying a PCMCIA to RS232 adaptor to connect the Focuser & 10D shutter release. Replace the PCMCIA bluetooth adaptor & GPS receiver with a wired USB GPS receiver. Then i would have to find an extra USB port to connect the GPS, so i will need a USB hub, for this i am thinking of getting the smallest most compact 2 port USB hub I can get hold of this can run the GPS & game pad & the remaining 2 ports on the laptop can run the Atik CCD & the Mount.

Option 2:

Buy a high quality USB hub with 3 or more ports & BrainBoxes USB to 2 port RS232 adaptor or FDTI chip USB to 2 port RS232 adaptor

In this configuration the 10d & gamepad will be directly connected to one pair of USB ports on the laptop, the USB hub will then connect to the mount, Atik CCD & the USB to 2 port RS232 adaptor which will connect to the focuser & 10d Shutter release, Leaving 1 free USB port on laptop & PCMCIA slot for GPS

Option 3:

BrainBoxes USB to 2 port RS232 adaptor or FDTI chip USB to 2 port RS232 adaptor Connected to the focuser & Shutter release & 2 port USB extension cable connected to the mount & Atik

Both of these will share 1 pair of USB ports on the laptop & the 10d & game pad will share the other pair of USB ports on the laptop. As in option 2 the PCMCIA slot will control the GPS.

Out of these options which seems better? Option 3 is probably the Cheapest & Option 1 is probably the most expensive

It would be nice to finally get rid of all these flaky bits of hardware and finally come up with something that works and is simple.

[nightvision]

I am just starting on the rocky road to imaging and I have already seen some of the issues you mention.

I recently did some checks on the mass of USB/RS232/Parallel lash-ups I am playing around with. I am trying to decide what set of interfaces to use when I finally build my first obs.

Identifying the cause of the failures and fixing them could be the best approach. Connection problems should be straightforward, consider getting some active USB cables. If you have the electronic skills build a heavily smoothed 5-volt supply for any hubs (or modify an existing supply). Also have a look at the USB over Cat5 converters like this CDL Micro - USB over Cat5e Extender - Product Details

The Cat5 standard is much better for solid connections and high data throughput in a noisy environment (differentially driven pairs). Keep the USB cables as short as possible and your hubs close the Laptop and try Cat5 to the Astro gear, not as neat but more reliable.

[RyanParle]

Well my problems seem to be coming from my USB hub, which works fine during the daytime when it is usually fairly warm & dry, however it gets flaky during the evening when the temperature drops & the moisture levels increase.

The usb hub is a powered type and included a regulated 5 volt 4 amp PSU.

Also my USB to RS232 adaptors can be problematic, One of them is fine, it is made by Magic Control Technology but the other which is a prolific chipset has a mind of its own, it has randomly changed its COM address without even being removed from the computer, and then there is the usual issue of it changing COM address if you plug it in to a different USB port.

I have given this lots of consideration over the last few days and have researched a lot of different USB hubs & USB to RS232 adaptors. Not many give specs for temperature, but a few of the industrial devices are rated to work as low as 0c, i have been advised that many of the consumer devices are only good down to the region of 7-10c, also many of the consumer USB hubs do not handle a mix of USB 1.1 & USB 2 devices very well and often choke when a lot of data is being transferred.

I am probably now going to get a different USB to serial adaptor, provided that the manufacturer can confirm it is fully compliant with the RS232 standard and has the normal 12v signal levels, It is the StarTech ICUSB2322X Professional 2 Port USB to RS-232 Serial Adapter

I am also considering the StarTech ST7200USBM Mountable Rugged Industrial 7 Port USB Hub Which will be able to handle all of my current USB needs as well as provide plenty of room for any additional hardware & with a bit of luck will be capable of running the 10d via the hub as well as the rest. This will be ideal if I can have only the 1 cable between the telescope & computer, but I have a feeling that the 10d will need to be connected direct to the laptop.