In a message dated 05/06/2010 16:18:06 GMT Daylight Time, dan...@verizon.net writes:
> 3...The series input and base to ground resistors on the RS232 interface > are both 180 ohms, rather than 10K and 3K3 respectively as in Didier's > circuit. > > If one wanted to use the RS232 interface to a computer at the same time as the ko4bb monitor in parallel, which I often do, then you would be well advised to stick to Didier's original values there. RS232 is quite robust, but still... I built one here quite early on to the original design and it has performed flawlessly ever since. I can not for the life of me figure out what oriental logic dictated these changes in the first place. ------------------ Hi Dan Many thanks for the comment. I was going to leave it as is, on the grounds that it worked ok up until now, but hadn't taken parallel operation into account and that's something I'll be wanting to do too so will take your advice and revert to the original. I also tried to figure out the logic for the change but with similar lack of success, and even searched via Google hoping I might at least find evidence of it being done that way before but found nothing. The last similar circuit I put together was a level shifter for interfacing RS232 to a 3.3 volt supplied Trimble Mini-T and on that I used a pair of 4K7s with the transistor accepting data from the RS232 port, "normal" values do seem to be around 10K each. ---------------------- And well done Nigel for getting to the bottom of this! --------------------- Much as I'd like to I can't really take the credit for this, it was Bob Mokia after all who alerted Leigh to the fix and I just followed on from there. If I'd taken one apart a few months back as intended, instead of dismantling everything in sight for a rebuild, we might have had a quicker answer, but that's the beauty of hindsight for yer:-) It would also have made life a LOT easier if the board had been designed such that it mounted with the component side uppermost. I'm sure then that somebody would have spotted and resolved this problem ages ago but unfortunately there seems to be an obsession with concealment in some quarters on the assumption that the world and his granny will rip off anything that's not nailed down. Of course that might be a fair assumption but, given the origins of this one, quite ironical too:-) regards Nigel _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.