Haunted Phone Guts!!

Going from breadboard prototyping to soldering onto a pcb is always harrowing.  I made this fritzing sketch to help me stay organized and remember what I’m doing.

This setup enables the phone to receive text string messages over serial to the arduino, which then rings the phone and upon pick up, passes the text message to the EMIC text-to-speech card, which then speaks the text.



Wiring up the EMIC was the easy part, but the bells on this old phone were meant to run off of AC power.  That means that to get the bell to ring with DC Power, I have to alternate the direction of current on my own.  I’m doing this using two sets of NPN and PNP transistors. Using 4 digital pins, I’m turning on and off the transistors in such a way as to provide power and ground through alternating sets of transistors, and feeding that to the bells.  What a pain!

Pin 2 on the arduino is used for the receiver switch.


I used an old deprecated arduino protoshield because I had one on hand. I also used Sparkfun’s Swiss Machined Female Headers for the transistors, because when I was breadboard prototyping they burned out a couple of times if the power was applied to the 12v rail before the arduino provided power to the transistors to act as gates. Using these headers makes it easy for me to be able to switch out the transistors if they burn out again, but hopefully they won’t.

I’m waiting on some wireless chips from ebay to get this completely installed into the phone, but other than that, it’s pretty much done(for now).

Eventually I’d like to add a functionality to be able to send 5 seconds of audio from the phone microphone to the website, but that gets into streaming and other more complex issues I’d rather not tackle at the moment.