Voip telephone ringing signal, trying to make a rotary phone ring! - Page 1
Forum section: electronics / beginners

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 16, 2022, 12:34:39 am
content: I was trying to make an old Ericsson cobra phone ring to incoming calls to no avail.At first I thought there was a problem with how I wired the ringer on the phone itself but now I'm sure there's something else at play here.On an old-school telephone line there should be a 90 (or thereabouts) VAC ringing signal when someone is calling you which is plenty for the buzzer to do its thing.But there's nothing showing on the scope when probing my VOIP phone line other than DC.Not sure what's the equivalent of a ring signal on a modern line..I don't see anything when I call myself..I tested the buzzer with an AC voltage of about 70V@20Hz and it rings so there's nothing else there preventing it to ring other than the line itself.Is my project doomed to fail?I can talk to and hear the callee but what good is that if you don't know when you're being called.I was looking for some kind of trigger or something but it's just DC..Really hope that I've missed something!

author: ledtester
author_rank: Super Contributor
timestamp: September 16, 2022, 01:17:11 am
content: This video might be of interest:KS0835F Telephone Subscriber Line Module -- Gadget Reboothttps://youtu.be/N3Z2zw0gRz8

author: Nusa
author_rank: Super Contributor
timestamp: September 16, 2022, 01:22:20 am
content: VOIP is basically messages over the internet. Triggering a ringing event when a call addressed to you is waiting to be answered would be a software event. Which one then uses to trigger a hardware action. It's not something you can "see" by looking at the raw signal without decoding.If you're not working at the API level and have a piece of hardware and/or sealed software package instead, you're probably out of luck if it doesn't provide such a feature.

author: Peabody
author_rank: Super Contributor
timestamp: September 16, 2022, 03:28:12 am
content: What phone do you normally have connected to your VOIP line? Does it ring? Do you possibly have some kind of call blocking set up on the VOIP line that's causing the calling number not to ring?I have an Ooma Telo VOIP system, and it definitely generates the ring voltage. And the Caller ID packet.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 16, 2022, 04:59:51 am
content: The thing to consider here is what VOIP stands for, which is Voice Over IP. On packet level there is the negotiation part that uses TCP/IP packets, and it is within these that the ring command is send. The voice part uses real time UDP packets.To make it work with an older analog telephone you need a conversion box. This box is attached to the network on one side, and on the other you can connect your analog phone. Not sure if these still use the 90VAC to make the phone ring.Or you can have an actual VOIP phone, which directly connects to the network. In this case there is no connection for an analog phone.Most phone connections that nowadays are called VOIP are terminated in the internet modem and are converted to analog phone outlets there. Not sure if these use the 90VAC either. In this case most internet service providers don't share the VOIP information with the client and you can't connect a VOIP phone to it.So the question here is what is it that you are using and try to connect to.

author: jonpaul
author_rank: Super Contributor
timestamp: September 16, 2022, 05:39:30 am
content: Ring POTS line 90 V 20 Hz in USA.Make a 90V 20 Hz bridge inverter, use a transformer or drive directViking Electronics model DLE-200Bj

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 16, 2022, 05:51:01 am
content: @jonpaul,I don't know what you get on the vikingproductstore page, but I get shit with porn on it, so check it please.Also the musson link seems a bit of advertisement for theater equipment?Edit: this is the correct link:https://vikingelectronics.com/products/dle-200b/

author: tooki
author_rank: Super Contributor
timestamp: September 16, 2022, 06:17:36 am
content: Quote from: belzrebuth on September 16, 2022, 12:34:39 amJust to clear up terminology: by “VOIP phone line”, do you mean the analog phone jack of some VoIP device? If not, can you elaborate?Assuming you do mean an analog jack on a piece of network equipment (such as your ISP-provided modem/router), please provide the model number so we can look up the specs. Maybe it’s outputting a much lower ring voltage (or current) that’s enough to trigger an electronic ringer, but not ring a mechanical bell.(A VoIP “line” doesn’t really exist as such. It’s packet-switched, not circuit-switched, using TCP/IP and UDP, with VoIP phones typically being connected via Ethernet or Wi-Fi.)

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 16, 2022, 09:41:49 am
content: https://openwrt.org/toh/vodafone/vodafoneh300sThis is the router I'm using, it is provided to me by the service I didn't choose it or specifically bought it.It's plugged straight into the wall and has two phone rj11 outputs.The phone plugs into the first one, the other plug marked #2 doesn't work AFAIK maybe it's for a second phone number.That's the whole setup!If I try to to plug the phone straight into the wall with an adsl filter it doesn't work.That was the older configuration, the way to have a landline now is to pass thru the router that's why I wrote it's a VOIP line, not sure about the details though.Edit: I enabled the second phone output on my router and plugged the phone there and bam! It rings.. really don't know why it works but it works!

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 16, 2022, 09:53:26 am
content: Your provider clearly upgraded from analog telephony to digital telephony. On ADSL there are two possibilities. It is either a separate digital channel on the phone line, or it it true VOIP, either way the modem should provide a proper ring signal for an analog phone. I have no experience with very old phones with mechanical bells for the ringing, but have used analog phones within similar setups and never had them not ringing.But it might be that your provider did not configure the modem properly.Since you linked to openwrt, it might be that you upgraded your modem to this software and that it has a bug. Or that you missed something in the settings.Edit: It seems you solved it while I was writing my post

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 16, 2022, 10:04:53 am
content: It seems that the phone 1 output is missing the AC voltage somehow, I can clearly see the 24.9Hz 90VAC signal when the telephone is ringing when probing output #2 but nothing shows on output 1.Maybe output 1 is for a cordless phone and 2 for a rotary phoneAnyways now off to figure out how to actually make a call..!I think there are plenty of ways for that on the net.

author: Tj138waterboy
author_rank: Regular Contributor
timestamp: September 18, 2022, 08:10:10 am
content: I'm not an expert on why but with AT&T newer gateways/modems most rotary phones and newer phones that have pulse dialing will not work to dial out. I believe it has something to do with dtmf type tones are the only signal that can be interpreted digitally.

author: tooki
author_rank: Super Contributor
timestamp: September 18, 2022, 12:08:48 pm
content: Quote from: Tj138waterboy on September 18, 2022, 08:10:10 amAs a blanket statement that’s clearly nonsense, since digital (as in, computer controlled) telephone switching equipment has been in use since the 1960s, with full backwards compatibility with pulse dialing.The people designing the analog jacks on VoIP gateways probably just concluded they could save a few cents by eliminating the circuitry and/or code to decode pulse dialing, since it’s not likely to represent a significant percentage of users. Or it’s even possible that the equipment can do it, but the telco simply disabled that feature so as to not have to provide technical support for it.

author: fordem
author_rank: Regular Contributor
timestamp: September 19, 2022, 02:30:52 pm
content: Google REN or ringer equivalence number - you'll at least have an explanation for why it's not ringing.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 25, 2022, 04:10:03 pm
content: Still struggling with this!I'm now in the process of trying to make it make calls and I will call it a wrap.I built a board of this project here :https://www.mattmillman.com/projects/building-your-own-pulse-to-tone-converter/But I have no clue where the pulse and dial contacts need to be connected on my phone.I'm lucky enough to have the schematic in a paper glued in the inside of my phone but I really find the schematic a bit weird to decipher..I initially thought that the dial and pulse points would be points marked "1" and "13" respectively but these points don't go to GND when the shunt goes closed or open..Of couse I've tried various other spots but I've yet to find a combination that works.Any help would be appreciated as this is getting annoying..!

author: Peabody
author_rank: Super Contributor
timestamp: September 25, 2022, 10:37:11 pm
content: My memory is that pulse dialing is just breaking and remaking the connection back to the central office. In fact, you could dial a number by just flashing the hook switch at the right speed. If that's correct, then the main twisted pair would be the lines you want to connect to.

author: David_AVD
author_rank: Super Contributor
timestamp: September 25, 2022, 10:58:13 pm
content: Some reading for you.https://en.wikipedia.org/wiki/Pulse_dialinghttps://www.rfwireless-world.com/Terminology/pulse-dialing-vs-tone-dialing.html

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 26, 2022, 04:40:31 am
content: The design given in the linkhttps://www.mattmillman.com/projects/building-your-own-pulse-to-tone-converter/seems to be based on modifying the existing wiring of the phone. It disconnects the dial disc from the phone line and connect it to the Attiny85 separately to be able to detect the pulses. The dial tones seem to be injected with the use of transistor Q1. I myself would add a series diode in the supply line to the Attiny85 instead of relying on the zener diode.Which connections in the schematic of your phone are for the dial disc is not clear to me, but it should be easy to detect by looking at the phone and follow the wires.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 26, 2022, 10:56:45 am
content: As I understand it I need to find a point (pulse) which connects to GND or the (-) point of the incoming pair when the dial is turned clockwise and shorts "n" times according to what I dialed in.I found that point where the dial when turned clockwise remains solidly shorted to GND and when the dial is left to freely rotate it shorts in clicks as per what number is dialed in.This is the orange wire.I also found another point (shunt) that connects to GND when the phone is picked up.This a light blue wire.There are more than one points where there is blue wire but only one that connects to GND when the phone is picked up.Orange is point "J" okay as per the schematic, the other one I don't know but it does what it should so I believe this is it.Connecting those to the circuit doesn't work though so maybe I should break the connection somehow?I just tapped on those and connected them to the MCU.BTW I used the second simplified schematic and the zener loses its temper after I while.I'm not sure it's a 1W zener but it certainly gets hot after a bit and votage begins to rise so I had to turn the circuit off.Maybe a series resistor would help or I really need to use a 1W zener for it to better tolerate the current that passes through?

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 26, 2022, 12:31:50 pm
content: I think it is best to disconnect the one end of the dial disc from the phone and only connect it to the circuit. Because you don't want the pulse signal on the line, you want the tones on the line.For the zener diode, it depends on the voltage drop over the series resistor how much current flows through it. Then that current times the zener voltage gives the amount of power it has to dissipate. Since you are connecting to a analog port on a modem there is no long line in between and the voltages might be a bit high. So measure them with the phone on the hook and with the phone of the hook to see what is needed in your case.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 26, 2022, 12:38:45 pm
content: Thanks so much for your help pcprogrammer.I'll try to disconnect the dial from the line what you say makes sense the circuit needs the pulses as inputs and the line needs the tones from the microcontroller.Also, I think that my readings are wrong, it's not the zener (while it gets a bit hot).I have 5V on the MCU when no other signal than line(+) and line(-) are connected as V+ and GND but things get messy when I'm playing around with other wires that most of them carry a 29V(!) or so potential to GND.Connecting those to the attiny was definitely messing with my readings; it's a miracle nothing happened to the attiny so far.I'll try putting some sense into this and post back.

author: macboy
author_rank: Super Contributor
timestamp: September 26, 2022, 12:41:58 pm
content: Quote from: belzrebuth on September 26, 2022, 10:56:45 amYou absolutely need a serious resistor. Did you forget to install R1 220 Ohm? I would look to increase this to more like 470 ohm, maybe higher. The 220 ohm allows too much current, well over 200mA. This means well over 1 W dissipation on the Zener unless something is constantly using much of that current. The microcontroller itself is not.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 26, 2022, 12:59:13 pm
content: I don't see any resistor on the schematic I'm using.It's a bit further down the page and it's using a 27V zener instead of the 5v1 on the first schematic.I'm also used in the typical vcc->resistor->zener->gnd scheme but this circuit is a bit different.It seems to be using the zener without a resistor as rough limiter of the regulator input voltage.

author: Nusa
author_rank: Super Contributor
timestamp: September 26, 2022, 01:24:56 pm
content: Correct, old rotary dials do mechanical switch pulsing on the release, not when your finger is winding the spring.And it was technically possible to dial only using the hook switch to create pulses. 10 pulses per second is the target, but the actual tolerance of analog phone systems was generous enough that a practiced human could get close enough.

author: rob77
author_rank: Super Contributor
timestamp: September 26, 2022, 01:49:31 pm
content: what you need is a voip gateway with a FXS port. connect the ethernet port to your network, FXS port to your old rotary phone. configure the gateway for pulse dialing.. and that's all you need.the you call your gateway's SIP address through SIP from your computer (or H323 or whatever protocol it supports) and it will workedit: adding a linkhttps://www.grandstream.com/hubfs/Product_Documentation/datasheet_ht801_english.pdfhttps://forums.grandstream.com/t/ht801-to-make-an-old-rotary-phone-call-need-phone-number/51201

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 26, 2022, 02:23:24 pm
content: Quote from: rob77 on September 26, 2022, 01:49:31 pmNice! But this phone is not mine to keep; it's meant to be a birthday present to someone that doesn't have a clue about what you're saying.It should be plug and play into the typical modem/router voip scenario that everyone's got at home nowadays.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 26, 2022, 03:36:42 pm
content: Ah a gift, that is nice. But the schematic you showed has some flaws.It needs a series protection diode and resistor in the supply line. It depends a bit on what the off hook voltage level is before the regulator on how big the resistor needs to be. I would also add a 10, 22, or 47uF capacitor before the regulator. Make sure it has sufficient voltage rating.Also make sure that the circuit is only under power when the phone is off the hook. For this it needs to be connected after the hook switch.Furthermore to make the dial disc work I would recommend the filter circuit used in the other schematic on the site you linked to. It needs at least pull up resistors to the 5V. Something like 10K, 4K7 or 2K2. Depends on what works best.What is also missing is the audio output for the tones to do the dialing. So you have to combine the two schematics to make it work.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 26, 2022, 03:48:23 pm
content: Quote from: pcprogrammer on September 26, 2022, 03:36:42 pmIf I manage to get it working that is, otherwise maybe a box of chocolates will do..The schematic is supposed to be working if the wiring is properly adapted to the device.Quote from: pcprogrammer on September 26, 2022, 03:36:42 pmSo GND of the whole circuit should be switched since I don't think that the positive line is switched anywhere, could be wrong on that though.Quote from: pcprogrammer on September 26, 2022, 03:36:42 pmI'm wondering how the author cut down on the first schematic and still managed to make it work.I'll see what I can do and report back on my progress.

author: rob77
author_rank: Super Contributor
timestamp: September 26, 2022, 04:29:23 pm
content: Quote from: belzrebuth on September 26, 2022, 02:23:24 pmit won't get any more plug & play than the gw with a FXS port... sorry.if you just want to make it ring for shits & giggles then it's 20Hz AC 60V RMS on top of a 48V DC what makes it ring (in other words 20Hz 60V AC with a 48V DC offset).

author: madires
author_rank: Super Contributor
timestamp: September 26, 2022, 05:49:11 pm
content: Quote from: belzrebuth on September 26, 2022, 02:23:24 pmVoIP capable routers come with a built-in VoIP ATA with FXS ports (for telephones). The VoIP ATA provides all required signals, like ringing and MWI. Many support the configuration of specific voltages and frequencies, some support pulse dialing. No need for additional circuitry to make the telephone ring!

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 26, 2022, 06:07:52 pm
content: I've already made it ring!It's on the first page.I'm now in the process of figuring out how to make it call..Perhaps rob77 didn't read the thread from the start and I didn't understand that he was talking about ringing only.

author: madires
author_rank: Super Contributor
timestamp: September 26, 2022, 07:24:41 pm
content: Possibly the Vodfone router doesn't support pulse dialing. In this case you can add a pulse to tone converter to the old phone.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 27, 2022, 07:07:24 pm
content: Okay I found the points I need to use.The pulse point is the yellow wire (marked 12 on the schematic) and the dial switch is the green wire marked 14.Disconnecting either of these from the phone PCB makes the phone dead when it's picked up. No dial tone is heard from the speaker.I thought I should disconnect the dial from the rest of the telephone circuit in order to isolate the pulse sending duties to the MCU and have the rest of the functions intact but doing that renders the rest useless.What am I missing here?It seems that yellow is connected to the line (+) on the bottom schematic ?I don't understand the weird switch contact symbols on the schematic

author: Nusa
author_rank: Super Contributor
timestamp: September 27, 2022, 09:34:24 pm
content: Top is the wiring diagram, which should match the physical unit we can't see. Bottom is the schematic, which is a lot easier to look at to understand the circuit. There's a one-to-one relationship between similarly marked points, although not all points are labeled on both.If it's not obvious, R=receiver, M=microphone, Bz=buzzer/ringer. AS = hook switch, contacts closed when off-hook. D = dial switch, and it looks like the microphone spring contacts to the carbon mic are shown on the wiring diagram (the M's in the D area). I'd say isolating the dialer is non-trivial from the mechanical and wiring point of view.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 27, 2022, 10:00:40 pm
content: Thanks for the info Nusa.What I'm trying to do is compare my phone to the simplified schematic posted here:https://www.hep.phy.cam.ac.uk/~lester/pv/Rotatone3.pdfThis a rotatone installation manual.This device perfoms a task similar to the one I DIYed.The guy who made the circuit I'm trying to install in the phone says that it should work if wired like a Rotatone.As I understand it the dialer circuit needs to be on the +ve side of the phone as well in order to short it out and transmit the pulses.So that's where the connection brakes and the receiving end of the phone dies out when the dial is disconnected.I think that the yellow cable connects to the +ve side thru a transformer as it's not reading as a straight short. I don't yet know what the dial switch (green cable) does.My reasoning of hotwiring these somehow would be that when you pick up the phone to receive a call you don't mess with the dial at all; so there must be a way of taking it out of circuit and keeping the rest of functionality the same, besides there are already a lot of people that have already done it!

author: belzrebuth
author_rank: Frequent Contributor
timestamp: September 29, 2022, 10:14:44 am
content: Okay there's some progress.I connected the yellow to green (the ends that go to the switch) and the receiver end still worked so I connected the points where yellow and green used to go to the MCU and it's actually doing something now!It seems to be dialing but I always get that the subscriber I've called does not exist.So there's something that confuses it.I know I'm a lot closer than before but maybe I missed something yet again.There's another pair of cables; brown and yellow those are normally closed and they go open when the dial is turned.I don't know what I should about those yet.I guess it prevents the phone from ringing when you dial?!Maybe I shouldn't bother with that pair at all.Any ideas of what might be the culprit of wrong numbers?Provided that the circuit I'm using works..

author: telephoneguy
author_rank: Newbie
timestamp: August 15, 2025, 02:33:50 pm
content: I know this is an old post however if you use the right VOIP ATA you can get good results. Grandstream is one of the few ATA's that both supports old rotary dial telephones and has enough ringing current to ring the old mechanical bells.A few years ago a TV program in the UK called " Find it Fix it Flog it" asked me to setup a simple intercom system (telephone line simulator) so they could dial and ring between two old 1920's rotary phones and I used a grandstream ATA (heavily software modified). The old phones worked really well.

author: Kenxomt
author_rank: Newbie
timestamp: October 03, 2025, 10:38:15 am
content: I tried doing something similar with an old rotary phone once and hit the same wall — VOIP lines don’t send the same high-voltage AC ring signal that old analog phones need. They just trigger a digital event instead. I ended up using a small adapter circuit that converts that signal into an actual ring pulse. At work we hadcall center softwarelike ActiveCalls that handled all that conversion cleanly, but doing it at home took a bit of DIY tinkering to get that classic ring back.

author: vallaska
author_rank: Newbie
timestamp: October 03, 2025, 02:06:20 pm
content: The ring voltage and cadence vary a lot depending on yourvoip provider. Some don't give the full 90V RMS or use shorter bursts that old rotary phones can't pick up well. I ended up using a ring generator circuit inline that mimicked the proper ringing signal, and it worked way better than relying on the ATA alone.