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.
