I once had the same problem with users voices falsing the DTMF decoder and causing the cover tone to be activated during voice conversations just like the original posters problem. I contacted the controller manufacturer, Peter at NHRC I think. He told me it is a comon problem with that decoder chip and to change a resistor to cause the time needed to reconize a valid digit to be longer. I dont remember the value or what resistor to change but it took care of the problem. I did a search for a data sheet for the decoder and the controller manufacturer followed the original circut to the letter so it wasn't their fault it falsed when set up properly and I took great care setting up levels with a scope so I know the problem was not on my end.
Hope this helps someone. tom > [Original Message] > From: Ron Wright <[EMAIL PROTECTED]> > To: <Repeater-Builder@yahoogroups.com> > Date: 3/30/2008 9:37:14 AM > Subject: Re: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller > > Nate, > > Chill out...take a pill, hi. > > The 3 V p-p is for the 8870/8880 internal op-amp level. Is it in stone? No, but found to be good level. This is not an input level to the circuit or IC, but is the internal op-amp output at pin 3 and what the internal parts of the IC is going to be decoding. > > How one obtains this is another design issue. The op-amp, as with any diff-amp, uses external resistors to set the gain. Simple op-amp design. Based on a given controller or other input if the gain needed is 2 then select the 2 resistor values correctly...if gain of 100 needed do the same. Again the 3 V p-p on pin 3 is a good measure to go for and again pin 3 is not an input from the outside world. > > I was responding to the post you sent to me and I made comments on it. Sorry you took it so hard. > > 73, ron, n9ee/r > > > > >From: Nate Duehr <[EMAIL PROTECTED]> > >Date: 2008/03/30 Sun AM 01:37:15 CDT > >To: Repeater-Builder@yahoogroups.com > >Subject: Re: [Repeater-Builder] False DTMF Muting On CAT-1000 Controller > > > > >Ron Wright wrote: > >> Nate, > >> > >> I've been designing 8870s and 8880s in things for over 15 years. Good chip and it has lasted. > >> > >> Pin 3 is simply the output of the internal op-amp and using a feed back resistor to 2 and driving with another one can set the AC gain over a wide range. The gain is feedback/driving resistor unless you wish to drive the non-inv input. The 1/2 Vcc source, pin 4, was cleaver by Mitel to simply use with a single 5 V supply. > >> > >> As to the other gain pins it is best not to use these for some other manufactures of the chip do not provide them. California Micro Devices, probably one of the biggest manufacture, does not. Really with the op-amp and allowing of adjusting its gain one does not really need these. > >> > >> For the 8880 the analog input is the real easy part. The CPU interface is much more difficult, but really simple design. The only same pin out of the 8870 to 8880 is the input op-amp. After that all changes. > >> > >> I normally do away with the steering circuit for RC adjusting the attack/decay decode times. I do both in software and tie pins 16 & 17 together on 8870, 18 & 19 on 8880. This give instant decode/release time, but use software for the timing. > >> > >> As with any op-amp using a dif amp, as the 8870 & 8880 do, single ended or dif input can be done. > >> > >> Looks like you cut and pasted your posting, hi. Referred to figures not included. Oh well. > >> > >> 73, ron, n9ee/r > > > >Sorry I'm going to lose it here for a moment... > > > >What does any of this have to do with the original assertion that 3V > >P-t-P is always right for a CONTROLLER, Ron? > > > >Drop the 8870/8880 debate. The information WAS cut and pasted, because > >it was directly from the datasheet for both devices. I figured anyone > >could find them with a Google search and read them. > > > >But I was letting you drag me down the rabbit hole anyway. Let's go > >back to the topic I asked about. > > > >You said 3V P-t-P is what you shoot for. > > > >I still assert that 3V P-t-P is... wait for it... > > > >NOT ALWAYS RIGHT ON EVERY CONTROLLER! > > > >No one talking about the a controllers is hooking their rigs directly to > >the damn Mitel chip. > > > >Maybe 3V P-t-P is right for a CAT. I don't know (nor care). > > > >If the CONTROLLER MANUFACTURER says: > > 2V P-t-P > > or 3V P-t-P > > or 10V P-t-P... > > > >*** THAT is what they designed to and what should be used. *** > > > >What does the CAT manual say? > > > >If the performance sucks at that level, the manual is wrong, or the > >controller is built wrong. Either way, doesn't matter for sake of the > >comment I was "correcting". > > > >----------- > > > >So... > > > >The discussion went from why DTMF doesn't always decode on a CAT > >controller properly... > > > >To a bunch of folks saying they usually lower the level going into their > >CAT controllers... > > > >To me saying "if the controller is done right, that's not necessary"... > > > >To you talking about 3V P-t-P and it was worded in such a way as it > >sounded like you meant ALL controllers want 3V P-t-P... > > > >To me saying the way you worded it made it sound like ALL controllers > >want 3V P-t-P... and there's usually manufacturer recommendations for > >setting such things properly in each controller. > > > >To us discussing the details of the Mitel 8870 and 8880... > > > >To us debating the details of how to put an 8870 or 8880 into a circuit! > > > >------------ > > > >HAHAHAHA... WHO CARES?! > > > >My point all the time has only been this: > > > >1. Feed your controller with what the MANUFACTURER recommends. > > > >2. If the controller doesn't decode well at the MANUFACTURER'S > >RECOMMENDATION, then they didn't design it right or they're clueless > >about their own decoder and their documentation is wrong. > > > >(NOT saying that about CAT... just saying it.) > > > >THAT'S ALL I was getting at. > > > >-------------- > > > >Maybe I should have just said... > > > >"My S-Coms when set to their recommended levels, don't false or do any > >of that strange DTMF wonkyness! Nyah nyah nyah! Pbbbbt!" > > > >Hahahahahaha... there. That better? More like a regular Internet > >mailing list, I suppose! > > > >(I was trying to avoid stooping to that level by instead pointing out > >that there are standards for levels published in good controller > >manuals. And those levels aren't ALWAYS 3V P-t-P!) > > > >The first way was much less likely to cause a mailing list flame-fest! > > > >Oh well. Flame away! I'll take Bob and Virgil's audio/analog > >engineering over a LOT of other things out there, any day of the week... > > > >So is the consensus that levels into a CAT have to be lower than what's > >recommended, or what? We never really got to the conclusion of that > >part of the discussion... what's causing all the DTMF flakiness for the > >original poster and other CAT owners that chimed in? > > > >I might find myself working on someone else's CAT someday (cough! > >haha... I won't buy one!) and need to know! (BIG GRIN) > > > >Nate WY0X > > > > > > > Ron Wright, N9EE > 727-376-6575 > MICRO COMPUTER CONCEPTS > Owner 146.64 repeater Tampa Bay, FL > No tone, all are welcome. > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > > -- > No virus found in this incoming message. > Checked by AVG. > Version: 7.5.519 / Virus Database: 269.22.1/1348 - Release Date: 3/28/2008 10:58 AM
