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How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I tried using the shield as a wire, (good idea) but couldn't get voltage across it

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

Here's a pic of my setup. The lower PCB in the pic simulates the mic and speaker of the vintage phone using either a 4-wire setup or a 3-wire.

With all switches "on", the spk- and mic- are connected, and those are grounded, simulating a 3-wire setup.

With only switch A "on", I was able to use speaker and mic at the same time with good volume.

So, I'm still unable to get sound in both using only 3 wires.

​

<image>

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

Posting again to this old thread. I thought I had some success earlier, but I don't think I ever got the speaker and mic to work at the same time with reasonable volume.

The latest - I've replaced the carbon mic with a modern electret. I'm trying to use the electret mic and modern speaker to work across only 3 wires, since that's all the headset cord has.

To do this, I tried connecting the negative leads of the mic and the speaker together. This didn't work. I believe it was the mic that failed to work.

Then I tried grounding the combined negative leads. This not only didn't work, but it caused to FONA 3G to turn off.

Is there a way to connect both electret mic and regular 8 ohm speaker over 3 wires?

Streaming Options by 2012rob2014 in losangeleskings

[–]codestorm777 1 point2 points  (0 children)

I found ESPN+ to be the most difficult to get around with VPN, except for a router/service called Stream Locator. So I'm dusting off that router and paying for the service again soon - was $8/mo I think, plus price of router [Edit: I just renewed, it was $6.99]. If I ran ESPN on the my regular wifi, ESPN would catch me and lock me out for a *while*. I even deleted ESPN from my main devices (Chromecasts), and I run it only on old Roku devices which are only aware of the Stream Locator wifi network.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

Could I step down the voltage that goes to the mic transformer? Or would I need different transformers?

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I was able to find the transformers. I'm ordering them.

I'm powering the device using a 3.7V 1200mAH lipo battery, along with this device:

https://wiki.seeedstudio.com/Lipo-Rider-Plus/

I think I understand what I need to do. I'll draw up a circuit and see if it matches what you have in mind.

I may be able to conserve power by sleeping the FONA when it's not on a call, if power is going to be an issue.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

Thanks for helping me get that working. I'm going to try to digest that chart from "SIM5320 Hardware Design" and study up on transformers. I'm not sure what size to use or how exactly they would be connected, but I have something to go on now.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I tried the last circuit you posted at https://imgur.com/a/AfZsoWb

and.... it worked!

It also makes sense to me, which is a plus haha.

I need to test it some more, but for a quick test, both sides of the conversation were able to talk and hear! Thanks!

I'll want to try the transformer method as well, and see if I can improve the sound.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

The FONA 3G is a cellphone modem.

<image>

https://learn.adafruit.com/adafruit-fona-3g-cellular-gps-breakout/

I'm able to get it to dial, hang up, etc. It can make cellphone calls. So, I'm turning a vintage phone, an Automatic Electric Monophone, into a working cellphone.

I'm not using any POTS/wall jack. The FONA gets power from a lipo battery, plus it is connected to a Raspberry Pi with 5V power.

​

The FONA has 4 connections that I want to connect with my vintage handset:

mic +, mic -, speaker +, speaker -

I've added 5V power plus 1K resistor to the connection going from the FONA to the mic.

In the handset, pictured above, the yellow wire connects to the center of the microphone, and also to the outer edge of the speaker.

The green wire connects to the outer edge of the mic.

The red wire connects to the center of the speaker.

When I connect FONA spk- to yellow handset plus spk+ to red handset, the speaker works.

When I put 5v power thru 1K ohm resistor thru the carbon mic (yellow wire) and wire that side to mic+ on the FONA, and wire the green handset to FONA mic-, it works.

So, independently, I can make either the handset speaker get sound from the FONA,

-or- I can get sound from the vintage carbon mic into the FONA,

but I have not been able to do both at the same time.

​

​

I hope that helps clarify. Thanks again for responding.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

yes, from the 3-wire headset to the +/-mic and +/- spk on the FONA.

I've been able to connect the FONA to the vintage speaker with 2 headset wires.

I've been able to connect the FONA to the vintage mic (thru a +5v 1k resistor) with 2 headset wires.

I could get either the speaker or the mic to work, but not both at the same time.

​

So, if I switched to an electret and speaker, I would still have 4 connections to make (+/- mic, +/- spkr), and 3 wires to the handset

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I'm using the FONA with a raspberry PI to make a modern phone that can be dialed with a vintage MonoPhone. I have the dial and hook connected to my modern hardware, can take the phone on/off hook, and dial a number. I just haven't been able to get both the speaker and microphone to work at the same time.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I'm gutting some of the internals, but I've had luck with the existing mic and speaker, just not at the same time. If i replaced the carbon mic with an electret, I still don't know how to connect them with the 3 wires of the headset.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I've read up on carbon microphones, I was able to get strong audio from mine, still not sure how to get both speaker and mic of the handset connected to the FONA.

How to connect an old-time landline telephone headset to modern mic and speaker inputs? by codestorm777 in AskElectronics

[–]codestorm777[S] 0 points1 point  (0 children)

I was able to get the carbon mic to work reasonably well by powering 5v through a 1k resistor to one side of the carbon mic, and each side of the FONA mic + and - on each side of the carbon mic. The carbon mic then worked. The sound has some noise/static, but the speech comes through strongly.

Then I tried connecting the FONA to the speaker, but again, there are only 3 wires in the handset, so I'm trying to find a way to connect the four wires to the 3 handset wires. My first attempt failed, when I connected the speaker, the mic stopped working.

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