> Unfortunately, much of the ham gear available uses bare, open > inputs and depends on the driving device to provide the voltage > and levels it needs at its inputs.
Let's see ... that would apply to the KRC2 in the "parallel input mode" along with the W9XT BCD-10 and the Yaesu Quadra for starters. On the other hand the TopTen Systems BD-Y, the original microHAM Band Decoder, the Yaesu FL-7000, and Tokyo High Power HL-1.5Kfx, have internal pull-up resistors. 73, ... Joe, W4TV > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Don Wilhelm > Sent: Saturday, March 07, 2009 2:56 PM > To: Roger > Cc: elecraft > Subject: Re: [Elecraft] [K3] Pull-up question > > > Roger, > > That is where the situation gets 'sticky'. It all depends on > what the > circuits at the end away from the K3 have implemented. You have two > pullup resistors on each line and 2 separate voltage sources. > > 1) If the voltage to the pullup resistors in the internal > device do not > match the voltage to the pullup resistors in the K3, there will be a > continuous flow of current through both pullups on any one > line when the > drivers are at their open, non-conducting state). If the > voltages are > close to the same value, this may not cause a problem, but if > they are > quite different (say one is 12 volts and the other is 5 volts), that > could create a big problem. > 2) The drivers in the K3 (when at the low level) must carry > the current > provided by both pullup resistors. Whether that is a problem or not > depends on the value of the pullup resistors and the current > capability > of the drivers. > > In my view of a good design, open collector (or open drain) > drivers are > the only thing to use. The terminating device can determine what > voltage is needed for reliable switching at its input and that device > controls the high level by providing its own pullup resistors. > Secondly, the pullup values can be sized according to the high level > input current required by that device and can control its immunity to > noise by controlling its input conditions. All is under the > control of > the external device designer. Unfortunately, much of the ham gear > available uses bare, open inputs and depends on the driving device to > provide the voltage and levels it needs at its inputs. > > 73, > Don W3FPR > > 73, > Don W3FPR > > Roger wrote: > > Mike Fatchett, > > OK, but what happens when you use > them with devices that already work without them,e.g. Array > Solutions 6 Pack and early band decoders? > > Roger K8RS > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
