Any Comms experts out there?

[steppenwolf]

Hi folks, I wonder if you can help with an RS232 problem?

I want to drive my telescope from my Sony Clie PDA using a serial port but although the PDA system works fine, I am informed that the RS232 levels are not high enough for the telescope so I need a TTL to RS232 level converter. I have now bought one but I cannot get it to work. The following is part of my email to the supplier:-

"Despite very careful testing, I am unable to get either device to work although they both show identical and repeatable results. I intend using the boards to control the movement of telescope under RS232 PDA control using Sony Clie Palm units. I already have RS232 port 'hotsync' cables for these devices. I know, however, that although the PDAs will connect and work with the PC with the lower level output available from the 'hotsync' cable, the telescope requires full RS232 levels to work hence the purchase of these devices from you.

As a method of testing the units, if Ie connect one of the PDAs to a PC and run a communications package on each device, they 'talk' to one another perfectly. However, if I connect the PDA to the PC using one of your devices, I get incorrect but repeatable results every time no matter what matching baud rate we select! The results are as follows:-

1. Typing text on the PC occasionally results in garbage on the PDA - no repeatability

2. Typing text on the PDA results in the wrong but repeatable character appearing on the PC. If we change the baud rate on each device, we get the same repeatable results.

I enclose two files:-

1. The wiring diagram of how the two devices are connected:- connect.jpg

2. The results of typing a character on the PDA:- binary.jpg

As you can see, I have done some in depth research to try and get these devices to work! CHR is the typed character, RESULT is what appears on the PC screen. I have even done a binary code conversion to see if there is a pattern to the errors. In fact, there is a pattern - note that typing a, b, c etc. results in the alphabet being produced backwards skipping one each time!! i.e. -

a=O

c=N

e=M

g=L

i=K

k=J

Needless to say, the PDA does not drive either of the two totally different Telescopes!

I am at a complete loss now and unfortunately, the whole project is stalled until we can resolve the issue."

Please can you assist?

[melt]

Am I missing something here, but the binary result is the hex value

Mel

[scott beeland]

 too many numbers for me so no help from here.

Kinda makes me glad I didn't listen in school

[steppenwolf]

Am I missing something here, but the binary result is the hex value

Mel

The second binary number is indeed the binary for the output HEX number (but sadly not the input HEX number which is of course what I want out!. I only reproduced the binary numbers as well so that I could look to see if there was a pattern in the individual changed 'bits' of data.

[melt]

Oh well!

Put brain back into relax mode

[steppenwolf]

What that's it - no solution? Come on Melt you can do better than that ...

[Blatman]

*Raises hand*

Look through the telescope, and adjust where you want to look by hand. Reliable, and *almost* totally fool proof, subject to hand/eye co-ordination issues

Or are you going for a look similar to Bruce Willis in "Jackal".

[DavidR]

Have been searching for a link in your problem because as you say "it's a systematic effect".

I think the hex representation of the result is slightly incorrect in your table in that the  hex 61 input you say comes out as a hex 79 but the binary you show is hex 4F.  This then matches the ASCII code for the results. If you go down the list making the adjustment the pattern appears to be

61 4F

62 27

63 4E

64  ??

65 4D

66 26 etc

Whilst it looks like a straight compatibility translation issue I can't yet track down from ASCII to what it is translating. Have tried VT100, UNICODE and ISO etc variations but no joy.

Call me ageek but I used to get paid for this sort of stuff. Now i'm hooked.

keep us posted  and will keep looking.

Good luck

David.

Will keep on looking but your email may get a faster answer.

[corsechris]

Steve,

Is the converter a self-powered device? If not, it'll likely never be any good for anything.  Could you tell me which device it is please (PM me if you'd rather avoid litigation from the vendor) and I'll see if I can come up with any useful suggestions.

Failing that, I can probably knock something together for you that'll work.

[steppenwolf]

*Raises hand*

Look through the telescope, and adjust where you want to look by hand. Reliable, and *almost* totally fool proof, subject to hand/eye co-ordination issues

Or are you going for a look similar to Bruce Willis in "Jackal".

This is a sort of valid point but I didn't get where I am today by not using technology to my advantage ..  

[Blatman]

The human body is the most advanced instrument you will ever own... at least, it was

[steppenwolf]

I think the hex representation of the result is slightly incorrect in your table in that the  hex 61 input you say comes out as a hex 79 but the binary you show is hex 4F.

David,

Now this is embarrasing, in the chopping down to a suitable chart size to post, I made an error in the heading - sorry, that heading should have been DEC, NOT HEX. I have corrected this to show the correct heading and included the HEX table as well - well spotted!

 

I was using VT100 on the PDA for the tests.

Thanks.

[Blatman]

I was using VT100

There's yer problem. Them Honda's are rubbish, especially for PDA/Telescope interfacing...

Have you tried using opposable thumbs?

[steppenwolf]

Steve,

Is the converter a self-powered device? If not, it'll likely never be any good for anything.  Could you tell me which device it is please (PM me if you'd rather avoid litigation from the vendor) and I'll see if I can come up with any useful suggestions.

Failing that, I can probably knock something together for you that'll work.

Chris,

The second item down (ACT-SIB) is the device in question:-

ACT-SIB

The supplier has been excellent in his response - highly recommended. He has suggested that the PDA is supplying more than 5v peak to peak (TTL) but not full RS232 levels which is enough to work correctly with the PC (but not the Telescope) but too high for the input to his device. He has recommended placing resistors in series with the data line but not knowing the current, I cannot use Ohm's Law to work out suitable values to try! Any suggestions.

[steppenwolf]

Have you tried using opposable thumbs?

Would you recommend that I try?