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I'm trying to create a project for my kitchen that involves using the shell of an old payphone and a modern cell phone ( perhaps iPhone ) to actually make calls. Basically, I would like the user to be able to pick up the receiver, press one of the number buttons, and have the unit auto-dail one of nine pre-defined numbers. With the microphone and speaker in the payphone being functional.

As I try to conceptualize a way to build this, here is what I came up with. Use an external iPhone microphone and speaker and place them in the handset. Use an actual iPhone as the unit that makes the call since I don't have anologue service at my house.

The part I'm a little unclear on is, how do I use the payphone button pad to somehow trigger the iPhone to make a call to 1 of 9 numbers in memory, and how do I terminate the call once the user hangs the phone up.

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closed as too broad by pipe, laptop2d, Dmitry Grigoryev, Wesley Lee, ThreePhaseEel Mar 10 '17 at 1:04

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Programmable bluetooth dev board and an arduino. \$\endgroup\$ – Daniel Mar 6 '17 at 21:25
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    \$\begingroup\$ Why an iPhone? You'll probably spend more trying to twist things to fit the iPhone than it would cost you to purchase a gsm-modem with analog connections. That, an arduino, and some buttons. \$\endgroup\$ – JRE Mar 6 '17 at 21:44
  • \$\begingroup\$ This was second on google search I used. - edevice.com/wirex \$\endgroup\$ – KalleMP Mar 7 '17 at 23:36
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    \$\begingroup\$ This sounds like a great project, but not such a great question on electrical design. Its too broad, if you need circuit help were more than happy to answer. \$\endgroup\$ – laptop2d Mar 8 '17 at 5:19
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I doubt an mobile phone would do it.

A GPRS Modem would definitely do the job, if it has microphone speaker terminals.

The key is the microphone and speaker connections.

Not a simple solution, the GPRS modem has a learning curve. At first glance it appears to be very similar to a regular land line modem, do not be fooled. it is nothing like a regular land line modem.

I have an old Multitech GPRS modem where the serial cable broke out to a separate phone jack.

Multitech no longer makes it. I was also buying knock offs of the Multitech out of China with a 20 piece minimum. There may be some of them floating around still. Ericsson Telecom made an inexpensive unit

This is NOT the one I have, but the connector is 15 pin video connector not a DB-9 as most GPRS Modems have.

GPRS Modem


Connector Pin out, notice mic and speaker.

enter image description here

PDF Manual GPRS Modem

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The listed method will work, but is a lot of hassle when it doesn't need to be. You can order a keypad for a Raspberry Pi that has the same keys a phone keypad would. From there, you plug it in and set your Pi up to make phone calls as outlined here.

What I would do is remove the payphones keypad and attach one connected to the PI.

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What you want to do is already on the market, usually called "retro handset". Those are typically just Bluetooth keyboards + audio devices which your smartphone pairs to, sometimes with a charging connector for the smartphone itself. There are also iPhone models which seem to work via the connector rather than Bluetooth.

You could probably buy one and fit the electronics inside your payphone, rewiring the microphone, the speaker and the keypad to the ones the payphone provides. You may need to modify the keypad of your payphone to make it compatible with the handset, but it shouldn't be too difficult.

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