Electronics > Beginners
Need help turning old payphone into dial-an-mp3 display
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Funvoyager:
Update...

Ok I think the reality of the electronics expertise and shortage of local resources is sinking in n

So. What I'd like to try on my own for "version 1.0" is a mostly mechanical fix. Here is my plan. ..

Open handset and take out everything inside. If I can't break into actual case of body then I cut the metal "cord" where it comes out of the phone case. Pull out wires.

Then put a headphone speaker in the ear piece and run the power wire down through the cable. Then insert the cut end of the cable with wire back through the hole in the case. Use a molly bolt type gizmo on the end of the cable so phone cable can't get pulled back out. 
Prior to this i could drill an exit hole in bottom of phone case so when I reinsert cable i can feed power line in and then back out bottom of phone case where I can discretely feed it to a hidden mp3 player a few feet away.
I can then add and remove songs manually and simply hit "play" dial down the volume so hopefully it can only be heard when receiver is out next to eat.

Version 2 can may be he inspired by the experience of using version 1 and inspire a future group of tech volunteer youths who come to my practice and immediately see how much better this could be by incorporating the great ideas shared here.

One final question...

I can't unscrew the earpiece and mouthpiece. Does it actually come unscrewed or is it glued so no one can tamper with it?  Maybe I need to use a special tool to create the torque i need. I wanted to ask in case I could ruin it otherwise.

I'll post pics or a link to pics when I get started.

Thanks again everyone.
Beamin:

--- Quote from: Funvoyager on September 11, 2017, 02:10:29 am ---Update...

Ok I think the reality of the electronics expertise and shortage of local resources is sinking in n

So. What I'd like to try on my own for "version 1.0" is a mostly mechanical fix. Here is my plan. ..

Open handset and take out everything inside. If I can't break into actual case of body then I cut the metal "cord" where it comes out of the phone case. Pull out wires.

Then put a headphone speaker in the ear piece and run the power wire down through the cable. Then insert the cut end of the cable with wire back through the hole in the case. Use a molly bolt type gizmo on the end of the cable so phone cable can't get pulled back out. 
Prior to this i could drill an exit hole in bottom of phone case so when I reinsert cable i can feed power line in and then back out bottom of phone case where I can discretely feed it to a hidden mp3 player a few feet away.
I can then add and remove songs manually and simply hit "play" dial down the volume so hopefully it can only be heard when receiver is out next to eat.

Version 2 can may be he inspired by the experience of using version 1 and inspire a future group of tech volunteer youths who come to my practice and immediately see how much better this could be by incorporating the great ideas shared here.

One final question...

I can't unscrew the earpiece and mouthpiece. Does it actually come unscrewed or is it glued so no one can tamper with it?  Maybe I need to use a special tool to create the torque i need. I wanted to ask in case I could ruin it otherwise.

I'll post pics or a link to pics when I get started.

Thanks again everyone.

--- End quote ---

There will be four wires in the cord to the handset thing. Two wires power the speaker and two power the microphone. You can take a digital multimeter to test which wires belong to which. This would be done by selecting the "ohms" setting and connecting the wires to the red and black leads. You will get a reading of 0 or some number when the proper two wires are connected. You can also use the "diode" setting which creates a beep sound on the meter when you have a connection. Touch the red and black wires on the meter together to see what sound and reading your meter makes. In theory  the pair with the lower resistance (closer to 0 or 0) reading will be the speaker. You can also try to plug the wires into your MP3 player until sound comes out. I would imagine the head set doesn't come apart to keep people from connecting "black boxes/blue boxes" (etc- boxes) to get free phone calls back when you could do that. If sound doesn't come out the reason is dealing with "impedance" of the speaker not matching what the mp3/amplifier can put out. Sounds simple but may a bit tricky. Remember a mp3 player will have 3 wires not four for the two speakers. This is because they share a common "ground" or "negative" lead. 
Beamin:

--- Quote from: skarecrow on September 06, 2017, 07:21:10 pm ---
--- Quote from: Beamin on September 06, 2017, 04:09:07 pm ---
--- Quote from: skarecrow --- The pi has stereo audio out, just a matter of connecting it up to a cheap 8ohm speaker in the handset etc.

--- End quote ---

--- Quote from: skarecrow ---  Nobody suggested adding a speaker.

Sent from my XT1565 using Tapatalk

--- End quote ---
:wtf:

By the way I tried this it makes some noise but its way too quiet to actually hear what it is. You can just tell that its connected but even putting your ear right up to it doesn't make an intelligible sound. You will need a simple amplifier circuit and a little output transformer.

--- End quote ---
That quote belongs to someone else. I assumed they just meant the speaker that's already in the handset, which is why I questioned if they were 8ohm because I couldn't remember.

Could you give some more details on exactly what you tried and with what equipment? Do you have a payphone also? The speaker output of a sound card should be more than powerful enough to drive a handset speaker. I've done it many times myself (with regular house phones though, not with a pay phone.). Back in high school I turned my 386 computer into a speaker phone by cutting a phone handset cord and putting some connectors on the wire to plug it into my sound card.

Sent from my XT1565 using Tapatalk

--- End quote ---

No offence but it sounds like you are just starting out in this hobby so I don't really feel you can adequately answer any questions I have that I haven't already tried when I was younger. Maybe do some more reading or watching eevlog videos.
Beamin:
What ever became of this? I wonder if the OP actually got this working. Would be an interesting product but I imagine holding a phone to your ear would be tiresome. Would also be interesting to see how long it took them, if they gave up in frustration, or if they are now on their way to a BS in EE.


What ever happened to all the worlds pay phones? I know the few that are left where I live have had the coins smashed out of them long ago or even had the whole thing removed for metal quite bold as there were located at busy bus stops and 100% chance someone would see you stealing it. A few months ago I was in the city a guy asked me "Do you know if there is still a 'coin phone' at the end of this street or where it went?" I explained in the 9 years I lived here I have never seen any payphones in this part of the city. I'm guessing he was jail for a very long time and didn't realize they give away free cell phones on every corner to low income people. A friend of mine got four of them when were walking around the city one day, probably could have got more if we tried. The phones were shit; one was three different colored sprint phones refurbished into a "new" one with a crooked paper sticker on it that said "budget mobile" covering the sprint logos. We tried calling customer service and it gave the options of using your credit card to buy minutes or customer service that didn't exist and would just play hold music non stop. I guess when you use all the minutes you just throw it away and go to the street corner and get another one. So wasteful and I bet these companies make a fortune off each one paid for by the $0.04 cent fee on our cell phone bills.
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