---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 03/12/20: 18 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:01 AM - Re: Two coms mic switching (Alec Myers) 2. 05:26 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III) 3. 05:58 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III) 4. 06:41 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Bill Boyd) 5. 07:52 AM - Re: Scan Mar 11, 2020 at 9.05 AM (user9253) 6. 08:26 AM - Re: Re: Scan Mar 11, 2020 at 9.05 AM (Bill Boyd) 7. 08:34 AM - Re: Two coms mic switching (Robert L. Nuckolls, III) 8. 08:39 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III) 9. 09:06 AM - Re: Re: Scan Mar 11, 2020 at 9.05 AM (DeWitt Whittington) 10. 09:47 AM - Re: Re: Scan Mar 11, 2020 at 9.05 AM (Charlie England) 11. 10:22 AM - Re: Scan Mar 11, 2020 at 9.05 AM (Bill Boyd) 12. 10:30 AM - Re: Two coms mic switching (cofford) 13. 10:44 AM - Re: Re: Two coms mic switching (Alec) 14. 11:15 AM - Re: Re: Two coms mic switching (Charlie England) 15. 11:36 AM - Re: Re: Two coms mic switching (Alec Myers) 16. 11:37 AM - Re: Re: Two coms mic switching (Carlos Trigo) 17. 01:36 PM - Re: Scan Mar 11, 2020 at 9.05 AM (Robert L. Nuckolls, III) 18. 02:04 PM - Re: Re: Two coms mic switching (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 05:01:28 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: Two coms mic switching I dont think you need to switch either side. Run the mic in parallel into both radios, and allow the appropriate PTT to select which transmits. > On Mar 11, 2020, at 19:31, cofford wrote: > Hello all, I'm sure this has been answered before, but I'm planning to use two com radios without an audio panel, so I need to switch the mic input. My current plan is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch the mic automatically. Does only the "MIC HIGH" side need to be switched, or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just a ground reference for the mic input, but I'm looking for the lowest noise solution. Thanks, Casey Read this topic online here: http://forums.matronics.com/viewtopic.php?p=495242#495242 ________________________________ Message 2 _____________________________________ Time: 05:26:32 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Scan Mar 11, 2020 at 9.05 AM > > >To the other questions, I have engaged Advanced >Flight to build one of their Advanced Quick >Panels for me, and those are based on their >Advanced Control=C2 Module just as others >sometimes build around an Approach Fast Stack >hub or a Vertical Power ECB box.=C2 I discussed >getting a legacy ACM with fuses from Rob >Hickman's inventory, and also having him wire a >panel without the ACM as a hub and using acres >of breakers or the modular fuse block bus >approach, and the ACM with ECB's won the >day.=C2 My purse, my calendar - my call. > >The airplane is an RV-10 with 17 feet of fat >wire to the starter spinning an IO-540.=C2 The 2AWG seems appropriate to me.=C2 =C2 > >The shunt, alternators and regulators are items >I've already purchased and installed in my >airframe.=C2 I'm here to make sure I'm about to >wire the regulators correctly for their intended use.=C2 Okay, plan-C: Put put a limiter in each b-lead with the limiters as close as practical to the alternator end of the shunt. Make shortest practical connection between battery end of shunt and the contactor. Agreed . . . 2AWG is a better choice for this distance. Sorry for the floobydust . . . I didn't recall our earlier discussions. I think you're good to go! Bob . . . ________________________________ Message 3 _____________________________________ Time: 05:58:59 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Scan Mar 11, 2020 at 9.05 AM >>>I assume=C3=82 that if sharing a Hall sensor is >>>permissible it is also permitted to share a 60A shunt. >> >>=C2 This is a 'real' shunt . . . not a hall-effect >>=C2 sensor? Yes, you can tie both b-leads to the >>=C2 anti-battery end of the shunt. > > Can't imagine where my head was at with that . . . > Obviously, this causes two alternators to share > a fault protection device at the far end of > the b-lead . . . a failure in one alternator takes > down both alternators. > > My bad. I owe you a six-pak . . . On further reflection, why run the aux alternator through this shunt? You have 'overload' monitoring with the SB1 controller. An alternator ammeter is of no value as a flight instrument . . . your voltmeter(s) tell you everything you need to know from a pilot's perspective. Besides, you can't 'overload' the aux alternator from the perspective of damaging it. 'Overloading' it only depresses bus voltage which is easily detectable on other instruments. I think I'd let the aux alt b-lead run right to the contactor and bypass the shunt. Current values are predictable and accounted for in your load analysis and plan-b protocols. Alternator load meters are limited to some troubleshooting studies on the ground. Bob . . . ________________________________ Message 4 _____________________________________ Time: 06:41:41 AM PST US From: Bill Boyd Subject: Re: AeroElectric-List: Scan Mar 11, 2020 at 9.05 AM I agree, Bob. Never had load meter on the 6A I built and flew for 22 years. Only added this because it was a standard feature on the new glass EFIS stuff. I like the idea of moving the standby alternator to the contactor because it gives me standby power if the shunt were to fail. I must say, the Dynon shunt appears well-constructed and the terminals and shunt bar beefy enough to withstand any expected loads "short of a short." In that event we have other more pressing problems best dealt with by opening the battery contactor... I have one other question - well, actually two: first, my original intent question from yesterday - do I have the wiring for these two regulators properly crafted as shown, for my goal of auto-switching and annunciation of standby alternator taking the load (despite this being otherwise deducible from EFIS voltage readouts and programmable alarms)? Secondly, what happens it the voltage sense to either regulator (terminal 3) is lost by a wire fault or a breaker trip? Seems like the regulator would sense an undervolt (namely, zero) and drive its alternator to max available output voltage. Will the OVP built into these units function off the other possible voltage sensing pathway (terminal 6 to the switch that brings power to the regulator circuitry), or will a loss of this voltage to terminal 3 result in a runaway overvoltage condition that nothing else in the Z-diagram can mitigate once the battery has soaked up all it can? I'm pondering the apparent vulnerability of this one wire (bus to sense terminal 3) to failure, especially adding additional failure points by running it to a breaker vs. a fusible-link. An inadvertent "open" on this wire just doesn't sound good. What can you tell me about that? Thank you for your time and tutelage, Bob. -Bill On Thu, Mar 12, 2020 at 9:05 AM Robert L. Nuckolls, III < nuckolls.bob@aeroelectric.com> wrote: > I assume=C3=83=9A that if sharing a Hall sensor is permissible it i s also > permitted to share a 60A shunt. > > > =C3=82 This is a 'real' shunt . . . not a hall-effect > =C3=82 sensor? Yes, you can tie both b-leads to the > =C3=82 anti-battery end of the shunt. > > > Can't imagine where my head was at with that . . . > Obviously, this causes two alternators to share > a fault protection device at the far end of > the b-lead . . . a failure in one alternator takes > down both alternators. > > My bad. I owe you a six-pak . . . > > > On further reflection, why run the aux alternator > through this shunt? You have 'overload' monitoring > with the SB1 controller. An alternator ammeter > is of no value as a flight instrument . . . your > voltmeter(s) tell you everything you need to know > from a pilot's perspective. Besides, you can't > 'overload' the aux alternator from the perspective > of damaging it. 'Overloading' it only depresses > bus voltage which is easily detectable on other > instruments. I think I'd let the aux alt b-lead > run right to the contactor and bypass the shunt. > > Current values are predictable and accounted for > in your load analysis and plan-b protocols. > Alternator load meters are limited to some > troubleshooting studies on the ground. > > > Bob . . . > ________________________________ Message 5 _____________________________________ Time: 07:52:27 AM PST US Subject: AeroElectric-List: Re: Scan Mar 11, 2020 at 9.05 AM From: "user9253" Do not forget a fuse or current limiter between the "B" lead and battery contactor. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=495255#495255 ________________________________ Message 6 _____________________________________ Time: 08:26:52 AM PST US From: Bill Boyd Subject: Re: AeroElectric-List: Re: Scan Mar 11, 2020 at 9.05 AM Good catch. Thanks! On Thu, Mar 12, 2020 at 10:57 AM user9253 wrote: > > Do not forget a fuse or current limiter between the "B" lead and battery > contactor. > > -------- > Joe Gores > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=495255#495255 > > ________________________________ Message 7 _____________________________________ Time: 08:34:08 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Two coms mic switching At 06:59 AM 3/12/2020, you wrote: > >I don=99t think you need to switch either side. >Run the mic in parallel into both radios, and >allow the appropriate PTT to select which transmits. > > > On Mar 11, 2020, at 19:31, cofford wrote: > > > > >Hello all, > >I'm sure this has been answered before, but I'm >planning to use two com radios without an audio >panel, so I need to switch the mic input. My >current plan is to use two PTT switches on the >stick, and tie the COM 2 PTT to a relay to >switch the mic automatically. Does only the >"MIC HIGH" side need to be switched, or do I >need to switch the "MIC LOW" side as well? I >think "MIC LOW" is just a ground reference for >the mic input, but I'm looking for the lowest noise solution. A DPDT switch routes PTT and MI HI to each radio independently. An example of this is shown in Figure 18-11 of the 'Connection http://www.aeroelectric.com/Books/Connection/18_Audio.pdf Bob . . . ________________________________ Message 8 _____________________________________ Time: 08:39:03 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Scan Mar 11, 2020 at 9.05 AM At 08:39 AM 3/12/2020, you wrote: >I agree, Bob.=C2 Never had load meter on the 6A I >built and flew for 22 years.=C2 Only=C2 added this >because it was a standard feature on the new glass EFIS stuff.=C2 =C2 > >I like the idea of moving the standby alternator >to the contactor because it gives me standby power=C2 if the shunt were to fail. They don't >=C2 I must say, the Dynon shunt appears >well-constructed and the terminals and shunt bar >beefy enough to withstand any expected=C2 loads >"short of a short."=C2 In that event we have >other more pressing problems best dealt with by >opening the battery contactor... true >I have one other question - well, actually >two:=C2 first, my original=C2 intent question from >yesterday=C2 - do I have the wiring for these two >regulators properly crafted as shown, for my >goal of auto-switching and annunciation of >standby alternator taking the load (despite this >being otherwise deducible from EFIS voltage=C2 readouts and programmable alarms)? yes >Secondly, what happens it the voltage sense to >either regulator (terminal 3) is lost by a wire >fault or a breaker trip?=C2 Seems like the >regulator would sense an undervolt (namely, >zero) and drive its alternator to max available >output voltage.=C2 Will the OVP built into these >units function off the other possible voltage >sensing pathway (terminal 6 to the switch that >brings power to the regulator circuitry), or >will a loss of this voltage to terminal 3 result >in a runaway=C2 overvoltage condition that nothing >else in the Z-diagram can mitigate once the >battery has soaked up all it can?=C2 =C2 Loss of sense lead shuts the alternator down. >I'm pondering the apparent vulnerability of this >one wire (bus to sense terminal 3) to failure, >especially adding additional failure points by >running it to a breaker vs. a fusible-link.=C2 An >inadvertent "open" on this wire just doesn't >sound good.=C2 What can you=C2 tell me about that? That was covered in the FMEA for the original design. Virtually ALL TC qualified alternator controllers are required to shut the alternator down if either (+) or (-) sense leads are opened. Bob . . . ________________________________ Message 9 _____________________________________ Time: 09:06:40 AM PST US From: DeWitt Whittington Subject: Re: AeroElectric-List: Re: Scan Mar 11, 2020 at 9.05 AM And then he shook Pence=99s hand. Dee > On Mar 12, 2020, at 11:23 AM, Bill Boyd wrote: > > Good catch. Thanks! > > On Thu, Mar 12, 2020 at 10:57 AM user9253 > wrote: > > > Do not forget a fuse or current limiter between the "B" lead and battery contactor. > > -------- > Joe Gores > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=495255#495255 > > > > > > > > > ________________________________ Message 10 ____________________________________ Time: 09:47:47 AM PST US From: Charlie England Subject: Re: AeroElectric-List: Re: Scan Mar 11, 2020 at 9.05 AM Heh heh heh.... Virus-free. www.avast.com <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Thu, Mar 12, 2020 at 11:20 AM DeWitt Whittington < dee.whittington@gmail.com> wrote: > And then he shook Pence=99s hand. > > Dee > > On Mar 12, 2020, at 11:23 AM, Bill Boyd wrote: > > Good catch. Thanks! > > On Thu, Mar 12, 2020 at 10:57 AM user9253 wrote: > >> >> Do not forget a fuse or current limiter between the "B" lead and battery >> contactor. >> >> -------- >> Joe Gores >> >> >> >> >> Read this topic online here: >> >> http://forums.matronics.com/viewtopic.php?p=495255#495255 >> >> >> >> >> >> >> ========== >> ========== >> Forum - >> class=""> href="http://www.matronics.com/Navigator?AeroElectric-List " >> rel="noreferrer" target="_blank" class=""> >> http://www.matronics.com/Navigator?AeroElectric-List >> ========== >> WEB FORUMS - >> rel="noreferrer" target="_blank" class="">http://forums.matronics. com >> ========== >> LIST WIKI - >> rel="noreferrer" target="_blank" class="">http://wiki.matronics.co m >> ========== >> Web Site - >> -Matt Dralle, List Admin. >> rel="noreferrer" target="_blank" class=""> >> http://www.matronics.com/contribution >> ========== >> >> >> >> > ________________________________ Message 11 ____________________________________ Time: 10:22:42 AM PST US From: Bill Boyd Subject: Re: AeroElectric-List: Scan Mar 11, 2020 at 9.05 AM Very reassuring. Thanks! On Thu, Mar 12, 2020 at 11:45 AM Robert L. Nuckolls, III < nuckolls.bob@aeroelectric.com> wrote: > At 08:39 AM 3/12/2020, you wrote: > > I agree, Bob.=C3=82 Never had load meter on the 6A I built and flew for 22 > years.=C3=82 Only=C3=82 added this because it was a standard feature on the new > glass EFIS stuff.=C3=82 =C3=82 > > I like the idea of moving the standby alternator to the contactor because > it gives me standby power=C3=82 if the shunt were to fail. > > > They don't > > =C3=82 I must say, the Dynon shunt appears well-constructed and the term inals > and shunt bar beefy enough to withstand any expected=C3=82 loads "short o f a > short."=C3=82 In that event we have other more pressing problems best de alt > with by opening the battery contactor... > > > true > > > I have one other question - well, actually two:=C3=82 first, my original =C3=82 > intent question from yesterday=C3=82 - do I have the wiring for these tw o > regulators properly crafted as shown, for my goal of auto-switching and > annunciation of standby alternator taking the load (despite this being > otherwise deducible from EFIS voltage=C3=82 readouts and programmable ala rms)? > > > yes > > > Secondly, what happens it the voltage sense to either regulator (terminal > 3) is lost by a wire fault or a breaker trip?=C3=82 Seems like the regul ator > would sense an undervolt (namely, zero) and drive its alternator to max > available output voltage.=C3=82 Will the OVP built into these units func tion > off the other possible voltage sensing pathway (terminal 6 to the switch > that brings power to the regulator circuitry), or will a loss of this > voltage to terminal 3 result in a runaway=C3=82 overvoltage condition tha t > nothing else in the Z-diagram can mitigate once the battery has soaked up > all it can?=C3=82 =C3=82 > > > Loss of sense lead shuts the alternator down. > > > I'm pondering the apparent vulnerability of this one wire (bus to sense > terminal 3) to failure, especially adding additional failure points by > running it to a breaker vs. a fusible-link.=C3=82 An inadvertent "open" on this > wire just doesn't sound good.=C3=82 What can you=C3=82 tell me about tha t? > > > That was covered in the FMEA for the original design. > Virtually ALL TC qualified alternator controllers > are required to shut the alternator down if > either (+) or (-) sense leads are opened. > > Bob . . . > ________________________________ Message 12 ____________________________________ Time: 10:30:15 AM PST US Subject: AeroElectric-List: Re: Two coms mic switching From: "cofford" nuckolls.bob(at)aeroelect wrote: > At 06:59 AM 3/12/2020, you wrote: > > > > > I dont think you need to switch either side. Run the mic in parallel into both radios, and allow the appropriate PTT to select which transmits. > > > > > On Mar 11, 2020, at 19:31, cofford wrote: > > > > > > > > > Hello all, > > > > I'm sure this has been answered before, but I'm planning to use two com radios without an audio panel, so I need to switch the mic input. My current plan is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch the mic automatically. Does only the "MIC HIGH" side need to be switched, or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just a ground reference for the mic input, but I'm looking for the lowest noise solution. > > > A DPDT switch routes PTT and MI HI to each radio > independently. An example of this is shown in > Figure 18-11 of the 'Connection > > http://www.aeroelectric.com/Books/Connection/18_Audio.pdf > > > > > > Bob . . . Thanks for the answers. Not switching at all would cause an impedance mismatch in my case as both radios have a built-in intercom so the mic input would always be live. Sounds like switching the MIC HI line is the way to go. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=495264#495264 ________________________________ Message 13 ____________________________________ Time: 10:44:43 AM PST US From: Alec Subject: Re: AeroElectric-List: Re: Two coms mic switching Im pretty sure microphones arent impedance matched; a mic input is a high impedance input and the mic is (?) 600 ohms, so running one into two inputs doesnt load the source. Sent from my iPhone > On Mar 12, 2020, at 1:27 PM, cofford wrote: > > > > nuckolls.bob(at)aeroelect wrote: >> At 06:59 AM 3/12/2020, you wrote: >> >>> >>> I dont think you need to switch either side. Run the mic in parallel into both radios, and allow the appropriate PTT to select which transmits. >>> >>>> On Mar 11, 2020, at 19:31, cofford wrote: >>>> >>> >>> >>> Hello all, >>> >>> I'm sure this has been answered before, but I'm planning to use two com radios without an audio panel, so I need to switch the mic input. My current plan is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch the mic automatically. Does only the "MIC HIGH" side need to be switched, or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just a ground reference for the mic input, but I'm looking for the lowest noise solution. >> >> >> A DPDT switch routes PTT and MI HI to each radio >> independently. An example of this is shown in >> Figure 18-11 of the 'Connection >> >> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf >> >> >> >> >> >> Bob . . . > > > Thanks for the answers. Not switching at all would cause an impedance mismatch in my case as both radios have a built-in intercom so the mic input would always be live. Sounds like switching the MIC HI line is the way to go. > > > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=495264#495264 > > > > > > > > > ________________________________ Message 14 ____________________________________ Time: 11:15:36 AM PST US Subject: Re: AeroElectric-List: Re: Two coms mic switching From: Charlie England That's kinda like adult diapers. (It Depends.) Most audio circuits are a low impedance feeding a high impedance, but you can't assume it's true in every case. You may well find high gain inputs that have their load impedance intentionally kept low, to reduce noise susceptibility when there's no source connected. On 3/12/2020 12:40 PM, Alec wrote: > > Im pretty sure microphones arent impedance matched; a mic input is a high impedance input and the mic is (?) 600 ohms, so running one into two inputs doesnt load the source. > > > Sent from my iPhone > >> On Mar 12, 2020, at 1:27 PM, cofford wrote: >> >> >> >> nuckolls.bob(at)aeroelect wrote: >>> At 06:59 AM 3/12/2020, you wrote: >>> >>>> >>>> I dont think you need to switch either side. Run the mic in parallel into both radios, and allow the appropriate PTT to select which transmits. >>>> >>>>> On Mar 11, 2020, at 19:31, cofford wrote: >>>>> >>>> >>>> Hello all, >>>> >>>> I'm sure this has been answered before, but I'm planning to use two com radios without an audio panel, so I need to switch the mic input. My current plan is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch the mic automatically. Does only the "MIC HIGH" side need to be switched, or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just a ground reference for the mic input, but I'm looking for the lowest noise solution. >>> >>> A DPDT switch routes PTT and MI HI to each radio >>> independently. An example of this is shown in >>> Figure 18-11 of the 'Connection >>> >>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf >>> >>> >>> >>> >>> >>> Bob . . . >> >> Thanks for the answers. Not switching at all would cause an impedance mismatch in my case as both radios have a built-in intercom so the mic input would always be live. Sounds like switching the MIC HI line is the way to go. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ________________________________ Message 15 ____________________________________ Time: 11:36:05 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: Re: Two coms mic switching I know. The nerdy part of me really really really wants to try it, to see if it works. On Mar 12, 2020, at 2:10 PM, Charlie England wrote: That's kinda like adult diapers. (It Depends.) Most audio circuits are a low impedance feeding a high impedance, but you can't assume it's true in every case. You may well find high gain inputs that have their load impedance intentionally kept low, to reduce noise susceptibility when there's no source connected. On 3/12/2020 12:40 PM, Alec wrote: > > Im pretty sure microphones arent impedance matched; a mic input is a high impedance input and the mic is (?) 600 ohms, so running one into two inputs doesnt load the source. > > > Sent from my iPhone > >> On Mar 12, 2020, at 1:27 PM, cofford wrote: >> >> >> >> nuckolls.bob(at)aeroelect wrote: >>> At 06:59 AM 3/12/2020, you wrote: >>> >>>> >>>> I dont think you need to switch either side. Run the mic in parallel into both radios, and allow the appropriate PTT to select which transmits. >>>> >>>>> On Mar 11, 2020, at 19:31, cofford wrote: >>>>> >>>> >>>> Hello all, >>>> >>>> I'm sure this has been answered before, but I'm planning to use two com radios without an audio panel, so I need to switch the mic input. My current plan is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch the mic automatically. Does only the "MIC HIGH" side need to be switched, or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just a ground reference for the mic input, but I'm looking for the lowest noise solution. >>> >>> A DPDT switch routes PTT and MI HI to each radio >>> independently. An example of this is shown in >>> Figure 18-11 of the 'Connection >>> >>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf >>> >>> >>> >>> >>> >>> Bob . . . >> >> Thanks for the answers. Not switching at all would cause an impedance mismatch in my case as both radios have a built-in intercom so the mic input would always be live. Sounds like switching the MIC HI line is the way to go. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ________________________________ Message 16 ____________________________________ Time: 11:37:55 AM PST US From: Carlos Trigo Subject: Re: AeroElectric-List: Re: Two coms mic switching Its kinda cool to assist these technically intrincated discussions Enviado do meu iPhone > No dia 12/03/2020, s 18:22, Charlie England escreveu: > > > That's kinda like adult diapers. (It Depends.) > > Most audio circuits are a low impedance feeding a high impedance, but you can't assume it's true in every case. You may well find high gain inputs that have their load impedance intentionally kept low, to reduce noise susceptibility when there's no source connected. > >> On 3/12/2020 12:40 PM, Alec wrote: >> >> Im pretty sure microphones arent impedance matched; a mic input is a high impedance input and the mic is (?) 600 ohms, so running one into two inputs doesnt load the source. >> >> >> Sent from my iPhone >> >>>> On Mar 12, 2020, at 1:27 PM, cofford wrote: >>> >>> >>> >>> nuckolls.bob(at)aeroelect wrote: >>>> At 06:59 AM 3/12/2020, you wrote: >>>> >>>>> >>>>> I dont think you need to switch either side. Run the mic in parallel into both radios, and allow the appropriate PTT to select which transmits. >>>>> >>>>>> On Mar 11, 2020, at 19:31, cofford wrote: >>>>>> >>>>> >>>>> Hello all, >>>>> >>>>> I'm sure this has been answered before, but I'm planning to use two com radios without an audio panel, so I need to switch the mic input. My current plan is to use two PTT switches on the stick, and tie the COM 2 PTT to a relay to switch the mic automatically. Does only the "MIC HIGH" side need to be switched, or do I need to switch the "MIC LOW" side as well? I think "MIC LOW" is just a ground reference for the mic input, but I'm looking for the lowest noise solution. >>>> >>>> A DPDT switch routes PTT and MI HI to each radio >>>> independently. An example of this is shown in >>>> Figure 18-11 of the 'Connection >>>> >>>> http://www.aeroelectric.com/Books/Connection/18_Audio.pdf >>>> >>>> >>>> >>>> >>>> >>>> Bob . . . >>> >>> Thanks for the answers. Not switching at all would cause an impedance mismatch in my case as both radios have a built-in intercom so the mic input would always be live. Sounds like switching the MIC HI line is the way to go. > > > -- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > > > ________________________________ Message 17 ____________________________________ Time: 01:36:45 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Scan Mar 11, 2020 at 9.05 AM At 08:39 AM 3/12/2020, you wrote: >I agree, Bob.=C2 Never had load meter on the 6A I >built and flew for 22 years.=C2 Only=C2 added this >because it was a standard feature on the new glass EFIS stuff.=C2 =C2 > >I like the idea of moving the standby alternator >to the contactor because it gives me standby power=C2 if the shunt were to fail. They don't >=C2 I must say, the Dynon shunt appears >well-constructed and the terminals and shunt bar >beefy enough to withstand any expected=C2 loads >"short of a short."=C2 In that event we have >other more pressing problems best dealt with by >opening the battery contactor... true >I have one other question - well, actually >two:=C2 first, my original=C2 intent question from >yesterday=C2 - do I have the wiring for these two >regulators properly crafted as shown, for my >goal of auto-switching and annunciation of >standby alternator taking the load (despite this >being otherwise deducible from EFIS voltage=C2 readouts and programmable alarms)? yes >Secondly, what happens it the voltage sense to >either regulator (terminal 3) is lost by a wire >fault or a breaker trip?=C2 Seems like the >regulator would sense an undervolt (namely, >zero) and drive its alternator to max available >output voltage.=C2 Will the OVP built into these >units function off the other possible voltage >sensing pathway (terminal 6 to the switch that >brings power to the regulator circuitry), or >will a loss of this voltage to terminal 3 result >in a runaway=C2 overvoltage condition that nothing >else in the Z-diagram can mitigate once the >battery has soaked up all it can?=C2 =C2 Loss of sense lead shuts the alternator down. >I'm pondering the apparent vulnerability of this >one wire (bus to sense terminal 3) to failure, >especially adding additional failure points by >running it to a breaker vs. a fusible-link.=C2 An >inadvertent "open" on this wire just doesn't >sound good.=C2 What can you=C2 tell me about that? That was covered in the FMEA for the original design. Virtually ALL TC qualified alternator controllers are required to shut the alternator down if either (+) or (-) sense leads are opened. Bob . . . ________________________________ Message 18 ____________________________________ Time: 02:04:45 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Two coms mic switching > >Most audio circuits are a low impedance feeding a high impedance, >but you can't assume it's >true in every case. You may well find high gain inputs that have >their load impedance >intentionally kept low, to reduce noise susceptibility when there's >no source connected. Keep in mind that the MIC HI input to an intercom or transmitter is designed to interface with a powered, amplified microphone. This is a legacy hold-over from the days when aircraft microphones were not unlike those in your telephone . . . carbon granules behind a foil diaphragm. https://tinyurl.com/htnn6nq This microphone is essentially a resistor whose resistance varies with audio stimulation. Hence it must first be biased up with some current so that the electronics can tap the resulting voltage variances that represent speech. Here's an exemplar MIC input circuit for a King transceiver . . . Emacs! Looking into the DC power path, the DC source impedance is on the order of 600 ohms, the AC load impedance is on the order of 390 ohms while the load impedance of the first audio stage is about 48,000 ohms. So while the voltage INPUT network may indeed be 'high' impedance, the microphone BIAS network is not. Further, paralleling two such inputs doubles the bias to any one microphone. The using DPDT "TX SELECT" switch for PTT and MIC HI lines is pretty much mandatory. 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