I was given a payphone by my neighbor (he had removed the actual phone assembly) and I'm not sure what I want to do with it, just yet. But I know that whatever I do, I will want to be able to use the different parts of the phone, inclduing the keypad. Therefore, I've decided to use an Attiny85 to modularize the keypad, sending the key pressed to another microcontroller (ie. an Arduino acting as a main controller) via I2C communication.

To read all the keys, I will be using a voltage divider with different resistors to actually read six keys on each analog input pin of the ATtiny85. I will explain this more when we get to the electronics.

Step 1: Parts


  • payphone with keys
  • ATtiny85
  • resistors: 12, 27, 47, 100, 150, 270 kOhm (2 of each)
  • wire (several different colors may be helpful, but aren't necessary)
  • heat shirnk insulation


  • computer
  • Arduino Uno
  • soldering iron
  • solder
  • screwdrivers of different sizes
  • chisel
  • breadboard
  • breadboarding wires
  • 10uF, 6+V capacitor (doesn't need to be 10uF, I used 4.7uF and I've seen others use 1uF)

I have also attached some useful resources that I frequently use during many of my projects.

<p>Very interesting. I've got an older keypad that is more mechanical to activate the DTMF tones. But now this instructable gives me some ideas.</p>
<p>Excellent! If you do, enter the project in the Remix Contest and link back to this Instructable :) </p><p><a href="https://www.instructables.com/contest/remix2015/">www.instructables.com/contest/remix2015/</a></p>
<p>And then send me the winnings? :)</p>
<p>no more vertical video. PLEASE :D<br>hold your phone horizontal</p>
<p>I hear you. Next Instructable, I'll do it properly, I promise :)</p>

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