usb to rs232

[Staffy]

I have the same problem trying to link up my GOTO to my PC. I found a RS232/USB adaptor lead on Amazon for just £1.65 which I ordered a couple of days ago. I'll let you know how I get on when it arrives.

[NickK]

I think the problem is that whilst older RS232 interfaces do genuinely run at 12V, whereas some modern ones and USB converters seem to run at 5V. When I'm running the signal over a fair length of cable it looks like the voltage drop is sufficient to make signal transmission unreliable.

This is the crux of most of the RS232 issues. Chips such as the FTDI FT232BM are natively 5V so attempting to drive 12V won't work unless there's a driver chip handling the 5V<->12V problem.

There's also speed. RS232 isn't the fastest thing out there, for example here's what the RS232 supports:

Data transfer rate of 300 Baud => 3M Baud (TTL)

Data transfer rate of 300 Baud => 1M Baud (RS232)

Data transfer rate of 300 Baud => 3M Baud (RS422/RS485)

So that's 1M baud, or about about 122 Kbytes/sec (not including protocol overheads or error correction). The FT232BM is a USB 2.0 Full Speed device (12Mb/s) so will not make any additional use of USB high-speed (480Mb/sec).

Oddly enough with my work on AOSX, I'm currently writing a transport plug in (a direct driver) for the FTDI FT232BM on the Apple Mac. The Atik camera I'm awaiting uses the FT232BM. I've also used it many moons ago for a seperate robotics project, so I know a shameful, freaky amount about this chip..

[irishcelt1962]

when i bought my serial to ubs no disc with drives came along with it. Does anyone know where i can download the drives . I have a EXT90 MEADE scope

thanks

irishcelt

[NickK]

when i bought my serial to ubs no disc with drives came along with it. Does anyone know where i can download the drives . I have a EXT90 MEADE scope

thanks

irishcelt

Ok it's normally possible to identify the chip that does the usb<->serial bit (normally hidden in the plug). From that we can see if there's a OS driver and then if your applications (or ASCOM/INDI) support it.

What operating system are you using?

If it's WindowsXP then go: Settings > Control Panel > System > Hardware tab in System > Device Manager.

Scroll down the list and if the cable isn't recognised then it's probably under "Other Devices" with an exclaimation mark against the name of the device (which may be something like "USB<->Serial Cable").

Select the unknown device and use the menu mouse button to bring up a small menu - select Properties from this menu. Next goto the Details tab. It should show you a drop down list and some text in the white box.

Select "Device Instance Id" from the drop down text and then copy'n'paste the text line in the white box, it should look something like this:

USB\VID_0403&PID_E548\22345821

This means:

USB - it's a USB device

VID - this is the manufacturer's identity 0x0403 (ie FTDI in my case)

PID - this is the product id 0xE548 (ie FT232BM chip)

The long number starting 22.. is the serial number of the FT232BM chip.

It's possible to get the same information form linux and OSX but I figure you're probably running windows xp.