Microphone proximity mute - Optogate alternative  - Page 1
Forum section: electronics / projects

author: hbt
author_rank: Contributor
timestamp: October 05, 2023, 12:47:32 pm
content: Hello everyone.I've been looking for a way to build a somewhat demanding circuit which by the sake of me and my limited knowledge can't really find a solution to.I'm a sound engineer and have been looking for a DIY solution for a problem many sound engineers face when mixing monitors. In many circumstances we used talkback microphones for the musicians to communicate with us during a live performance which we have open constantly in our monitor mix.There's a commercial solution called Optogate which has a proximity sensor which opens the microphone when the musicians get near the microphone to talk back to us. This solution works on phantom power which brings the biggest problem on designing a workable solution for the problem at hand.Due to the restrictions imposed by the phantom power specs which limits us to a 48V 10mA power supply.The principle used to do this is using a optocoupler which opens and let's the microphone signal once the proximity sensor detects a presence in front of the microphone.Although it seems a seemingly simple circuit, there's no place I can find a set of components which is able to work with said limitations.I'd like to challenge the more knowledgeable people on the matter to help me out developing such a circuit which has been wanted by so many in my line of business for so long.Any help would be extremely appreciated.Thank you all in advance.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 05, 2023, 05:36:45 pm
content: Are you looking for the optocoupler part specifically? Or the proximity sensing? Or the entire system?If I recall correctly, the H11F1 - H11F3 are often used as analogue switches for audio and are still available at Mouser. For alternative muting circuits, Elliot Sound Products is a great resource for audio DIY:https://sound-au.com/articles/muting.htmlI've used CMOS analogue switches (4066, and the MUX's 4051/4052/4053) before and didn't notice any degredation in audio quality - but thats just my ears. As this is a monitor rather than high quality recording system, I suspect you don't require very low noise or flat response - its just talking isn't it?As for proximity sensing, I have no idea what these systems use, but I imagine ultrasonics is out (plus its pretty old tech when there are much better solutions) and microwave "body" sensing is a bit too much for such a simple - and close - proxmity sensing. Do they use optical? I did design a proxmity activated LED light years ago design for low power (2 AA batteries lasted about a year) but it was quite involved and used a microcontroller.More details on what exactly you want to build/achieve would probably get more responses.

author: hbt
author_rank: Contributor
timestamp: October 05, 2023, 06:48:35 pm
content: Thanks for your reply.The H11F1 may be a possible solution for what I can understand.As for the purpose, I apologise but I don't think I was very clear on the path of signal I was considering.Let me try to clear this a bit better.As we deal with XLR plugs and balanced signals the optocoupler should be used to shunt the positive and negative signal of the balanced signal, meaning that the coupler being open, won't affect the signal passthrough from the microphone to the console.I just need to shunt two of the XLR wires when no one is in front of the microphone, indeed muting it.She sensor used on the Optogate PB-05, which is the commercial solution and too expensive for the purpose, is a optical proximity sensor if I'm not mistaken.It may be easier to show the commercial solution at the linkhttps://optogatesolutions.com/.This is what me and many sound engineers would like to develop in a DIY fashion.

author: eleguy
author_rank: Regular Contributor
timestamp: October 05, 2023, 07:14:17 pm
content: Does not sound too complicated business. Search a book "Small Audio Signal Design" by Douglas Self and you find almost everything else but not the "distance" part. Here the search engine is your friend and proximity sensor/switch is the keyword.

author: themadhippy
author_rank: Super Contributor
timestamp: October 05, 2023, 07:38:31 pm
content: Quotethats a new one on me,and i spent many years down that end of the multi.Talk to stage mics were either switched on the desk or on the mic, and stage to desk was either hand signals ,or a shout across the stage.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 07, 2023, 12:54:01 pm
content: Ahh so its the whole system - both presence/proximity detection, as well as the muting?The muting will be the easy bit - already plenty of good solutions mentioned. The tricky bit is proximity sensing - it looks like they went with IR because it is the most reliable and least likely to interfere with audio equipment.There are IR proximity sensors that are much smarter than just an IR LED and photodiode: like the VCNL4040https://www.vishay.com/docs/84274/vcnl4040.pdfAs you only really need to detect 15-20cm these solutions are less painful than designing something completely from scratch, as you'll have to deal with a large range of ambient lighting - plus man made lighting switching frequencies, all of which an integrated solution filters out leaving you with a basic "yes/no" for proximity.Although most of these are so integrated they use I2C - so you'll need a small microcontroller to use them, I believe there are more IR sensors out there designed for proximity and low power - like the TSSP40:https://www.vishay.com/docs/82458/tssp40.pdfThis still needs the LED source to be modulated (at 38kHz, like most tv remotes) but you can adjust the range by adjusting the power of the IR LED. And its pretty low power.A quick google in the usual "maker" places I gound the following:https://learn.adafruit.com/using-vcnl4010-proximity-sensor/https://wiki.seeedstudio.com/Grove-80cm_Infrared_Proximity_Sensor/- this has a very high current consumption but roughly measures the range - so you can set the distance it detects athttps://learn.adafruit.com/adafruit-apds9960-breakout- overkill as it also detects guestureshttps://thepihut.com/products/pololu-distance-sensor-with-pulse-width-output-50cmhttps://thepihut.com/products/fermion-vl6180x-tof-distance-ranging-sensor-breakoutTheres loads of solutions about but each has its own hassles - like being so integrated it needs a fair bit of code to just configure them. But if you're trying to design a comercial system, and one that competes with the one you linked you'll need to do a fair of research and testing.

author: Marco
author_rank: Super Contributor
timestamp: October 09, 2023, 02:15:56 pm
content: Quote from: hbt on October 05, 2023, 12:47:32 pmYou seem to want a minimum component minimum size solution, which is the only thing which makes this an interesting exercise. 48V/10mA is an enormous power budget for a complex solution.If you want to shunt it with an optofet, you should probably put some 10K resistors in the signal lines in both directions, that way if the microphone or input is relatively low impedance it gives the shunt more to divide against.PS. probably want to use a coupling capacitor to the shunt too, so you're not shunting the phantom power.

author: hbt
author_rank: Contributor
timestamp: October 10, 2023, 08:54:00 pm
content: Thanks for your reply.I've been a sound engineer for over 27 years.The purpose of the solution that I've been looking into makes the job and the inear mixing more efficient and better sounding for everyone involved.The artist I want to use this solution on has a 4 elements band on stage and they're all on inears. As we have a lot of bleed into the stage because of monitors, PA and the instruments (drumkit, guitar amps and DJ booth) the sum of said bleed on 4 open microphones for talkback mask out any clean mix that you're making for inears. The DJ is the only one who is able to actually open the microphone with it's hand or a foot switch. While the others are playing, they all use their hands and feet, which invalidates a switch solution.As on my own mix, I also have all talkback microphones open, so they can get my attention without making gestures which I may not see. The automatic process of the microphones opening only when they actually need to talk, without any further action is a blessing.I say this, because I actually have used the Optogate solution in the past and it really is a great way of minimizing all the problems inherent to the specific need of talkback microphones.This way the musicians can also talk to each other because of any variation or musical direction they may need to let the others know about, or even just so they can go over a phrase one more time and make sure all are on the same page, just because the singer decided to prolong an interaction with the audience. Having the microphones bleeding into their inears all the time is not a viable solution, since it actually ruins the mix and it's a lot more tiring playing with unwanted noise on your ears.

author: hbt
author_rank: Contributor
timestamp: October 10, 2023, 08:57:11 pm
content: Thanks for all the information.And yes, it is a proximity sensing auto mute function that we're talking about.My main problem is like you say, the proximity sensing solution and one that doesn't need any active components that require more than 10mA.I'll look on what I can gather from some information you sent, which I didn't know about.

author: hbt
author_rank: Contributor
timestamp: October 10, 2023, 09:02:41 pm
content: Thank you, @Marco.The muting part is not my main problem. That one can be done with an optocoupler without much to worry about.My main problem is the distance sensing circuit to control the optocoupler.As for the power consumption, yes, it is about 0,48 W. But if you start considering a voltage regulation and the sensing circuit, the current needs start adding up. If you have any idea of a working solution for both, the muting and proximity sensing circuit, I'd love to discuss it with you.

author: Marco
author_rank: Super Contributor
timestamp: October 11, 2023, 10:35:53 pm
content: You can use either infrared reflection or ultrasonic reflection (not distance measurement, just plain CW on the transmitter and then measuring received strength on a separate sensor and switching on when it crosses a threshold).Optogate seems to be using infrared (short wave infrared, not thermal).

author: Marco
author_rank: Super Contributor
timestamp: October 12, 2023, 12:14:51 am
content: If I were to take a guess, they probably add a lock-in amplifier, since it's so easy to do.Just modulate the LED with a square wave, capacitively couple the received signal and chop it with the same square wave before low pass and thresholding.

author: Marco
author_rank: Super Contributor
timestamp: October 12, 2023, 08:15:59 pm
content: Quote from: Terry Bites on October 11, 2023, 10:51:48 pmTI trying to replace a simple coupling capacitor with an opamp :p Except for extreme corner cases, this is never going to make sense.Looking around all of the integrated IR proximity sensor solutions are digital, so you would probably have to design a complete circuit yourself if you want something simple and analog.PS. why not just buy those OptoGates? 200 Euros ain't bad.

author: MathWizard
author_rank: Super Contributor
timestamp: October 13, 2023, 03:01:54 am
content: Quote from: Terry Bites on October 11, 2023, 10:51:48 pmWhat do you mean keep clean from? I don't remember or know enough details on currents in metals. Does higher current over time erode away any oxide layer, or does it make it worse ? Do big high power relays have problems over time if you don't use enough current in them ?Also unless it's for hands free mic use, what about just some push button thing on the mic ?

author: Buriedcode
author_rank: Super Contributor
timestamp: October 13, 2023, 12:10:36 pm
content: Quote from: MathWizard on October 13, 2023, 03:01:54 amI believe that is the point of the thread, many have focused on the muting part, but I think the proximity sensing is more troublesome.

author: Bud
author_rank: Super Contributor
timestamp: October 13, 2023, 01:09:04 pm
content: Can you use a pressure sensitive switch in form of a floor mat in front of the micrphone stand?

author: MathWizard
author_rank: Super Contributor
timestamp: October 13, 2023, 02:44:14 pm
content: Well maybe this would be bad around audio circuits, but what about a theremin type circuit? I can't remember how they work, but what if instead of making sounds of changing pitch with proximity, it controlled some switch ? IDK if the mic is fix in 1 spot, hands free, etc.

author: themadhippy
author_rank: Super Contributor
timestamp: October 14, 2023, 12:08:56 am
content: could always go ole skool with 2 mics out of phase ,no switching required.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 14, 2023, 01:10:33 pm
content: Mic Phasing! Phasing WTFIT! We have sensitive youth on ths blog mister, please dont panic them.RFID tags, the ones that stop you nicking the meat from Sainsbury's.Just stick 'em on your stripey jumper.

author: Bud
author_rank: Super Contributor
timestamp: October 14, 2023, 03:56:14 pm
content: I'd think a solution should Not require the musicians to have to carry RF cards, tags, tokens. Those things always get dropped, lost, forgotten, broken etc. the moment you need them.

author: CaptDon
author_rank: Super Contributor
timestamp: October 15, 2023, 04:14:27 pm
content: I am baffled by your terms 'talkback microphone'. Is this separate from the 'normal' vocal microphone which feeds the front of house mix? What is the normal vocal mic, is it part of a headset or is it on a mic stand on stage? It appears from your text you have two separate microphones, one for talkback and one for front of house / monitor use? Where are these microphones placed? My 'talkback' microphone is at the mixer board so I can talk to the band through the monitors. I haven't run into the exact problem you have since usually if a monitor adjustment needs to be made the band member just makes his/her wish known through the normal vocal mic. although I do watch for agreed upon visual clues during a song. I am interested to know more about your setup. Seems like everyone is going to in-ear with headset boom mics. and yet we still have a bunch of stage monitors. It gets to be double the fun when you have a monitor board and engineer in addition to a front of house board and engineer and suddenly there is an ear shattering feedback and both engineers look at each other with that "It isn't me' look on their face.

author: themadhippy
author_rank: Super Contributor
timestamp: October 15, 2023, 04:39:11 pm
content: QuoteNever.its always the FOH geezers fault,either that or the so called talent doing something stupid.QuoteFor at least one artist i worked with it was to get some "feel" back on stage to overcome the isolation they felt with in ears,even with ambient mics. Also a wedge is a great poser platform,one foot on the wedge is a classic rock stance.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 19, 2023, 12:05:17 pm
content: The man's right, those TSOP Rxs are very sensitive. But then they are very selective.But just for fun on a slow day, I've gone cheap as.I had few channels of IR in the same room and they didn't interfere with each other.Watch out for the man with the TV remote.I think if you were getting serious you'd use a micro to send and check the RXd code.C6 was 330n not 1u. You can tweak it for release delay (270n minimum I found).I used a CQY37N 950nm IR LED, its pretty tight on beam angle.The 4093 oscillator and it didnt drift very much with temperature and battery voltage.You do have to tune up the TX osc properly because these receivers are narrow band.The average draw from 48V was 3.7mA without the relay.<$10 including the gating relay or opto.A relay is still the easiest no fuss way to go. You want a 48V coil to keep the current down.eg TX2-48V only needs 5.6mA to pull in. I'd taken the relay power from both sides of the pair.That shares the current and any pop.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 19, 2023, 02:16:58 pm
content: Nice idea, but unless you really limit the IR LED's current its going to sense proximity at a few metres. Those TSOP IR recievers are extremely sensitive. Lock-in amplifiers and autocorrelation have been mentioned in this thread, and both would suit the use of the TSOP38xxx series.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 19, 2023, 03:03:23 pm
content: The makers of this thing say its not a studio widget, its stage thing.kW of PA will drown out talk back from an open mic they say.How does the vocalist manage to be heard I wonder?Steaming BS I think.I notice the same people make a mute footswitch. Only $200, wow.I wonder how that works, I'm sure they keep that secret. Its balanced line so very tricky.Who would would have thought of such a crazy pedal, pure 'kin genius. Walk towards it and stomp!They give a list of bands that have foot trouble.

author: themadhippy
author_rank: Super Contributor
timestamp: October 19, 2023, 04:40:18 pm
content: Quotemore to do with having constant noise coming out your listen wedge from the open shout mic,you might miss something important ,like the shout announcing the beer rider has been refilled.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 22, 2023, 09:07:29 am
content: ho hohttps://www.amazon.co.uk/Waveshare-Infrared-Proximity-Sensor-Obstacle-Avoiding/dp/B01MTPEIM3