Hacking old payphones

Hello all.

I'm part of a group applying for a grant to activate a public space. The design that we've come up with involves six old payphone booths. As people pass by the phones or open the door to one of the booths, they will ring. When the receiver gets picked up the phone will play a pre-recorded message - three of the phones will play messages about the history of the space, two of them will play messages about the present, and one will play a message about a possible future.

As far as I see it (and I'm no electronics expert so please let me know if something is glaringly wrong) there are three systems we've got to work out. Firstly, the phone needs to play a recording when it is picked up off of the receiver. Secondly, there need to be some motion sensors on the outside of the booth that will pick up passersby and make the phone ring, but not be so sensitive that the phone is constantly ringing (the space is moderately busy and in a cultural-center/touristy part of town, and about three dozen people pass through it every ten minutes or so). Thirdly, the phone needs to ring when the door of the booth is opened.
We've been trying to get ahold of some of the old phone booths that our city took out in the last few years, but if we can't get any of those we're planning on using something like this and building a booth for it: Decorative Telephones You'll Love in 2021 | Wayfair.ca

I was wondering if you guys think that an Arduino is the appropriate tool to use to get the phone to do this? Could it handle all three operations for all six booths, or would we need one Arduino per phone booth? I've got some very preliminary experience with Arduinos and electronics, but it was a few years ago and I would call myself pretty much a novice. Is this too ambitious? We do have several months in which to plan (this project would go up in the summer), but are trying to get a final budget together soon.

Thanks a lot! We're excited about getting this project going.

You need one per booth unless they're all really close to eachother. Project itself sounds straightforward. You need a separate board to play the mp3, but mp3-player modules are dirt cheap on ebay. That, a PIR motion sensor, physical or magnetic switch on the door, and receiver switch... I'd use pro mini's for the arduino as they're cheap and have less battery-draining baggage, since I assume these will need to use batteries. (and you'd remove the power light from them too, to save battery)

I guess you'd also need a ringer of some sort. This might be the biggest battery-drainer of all if you want it to sound authentic.

If the ringer works like one of the old standard phones, it takes 70 - 90VAC 20 Hz which requires special circuitry to generate. An example of a ring module is given at Sparkfun, for a project they did to turn an old rotary telephone into a cell phone.

Ringer circuit

That sounds like a really fun project, and one that Arduino technology is well suited to.

For the motion sensor, you will probably need to experiment with shielding the PIR (passive infra red) sensor, as they are typically way too sensitive. For the ringer, you might want to use a transistor interface to a phone capable power supply. And as others have said, get a cheap MP3 board for the recorded message. For extra fun, perhaps have any two phones that are answered simultaneously connect with each other. It would add a level of surprise to the installation.

Have fun with it all Drocki!

For the proximity sensor I'd go for one (or two - wider coverage) ultrasound sensors rather than PIR.

PIR sensors sense everyone in a 5-meter or so radius. That's probably way too much. An ultrasound sensor will be able to detect presence up to about 3 meters, but gives you a range so you can have your software react only when the distance to the object (the person) is less - say 1.5 meters.

Also ultrasound has a detection cone of only about 30 degrees, so it's quite directional. One or two of those sensors will allow you to cover the area of interest.

For practical reasons I'd go for one Arduino per booth. Will be much easier to implement even if the phone booths are close together. Indeed wav player for the messages, and put a modern day microphone in the receiver.

I think you will also need to supply a battery to the phone. The phone system battery is -48v (with the audio riding on it). Not sure how low a voltage will work. Try different standard batteries. When you hear the message, your good.

Why phone battery?

If I were to take on a project like this, I'd start with COMPLETELY gutting the existing phones' electronics, which are probably a few decades past their sell by date anyway. The inside is totally irrelevant to the end user - they just need to hear the ring and the message. The outside has to be the same (the phone booth, receiver, etc), everything else can be transplanted. Those old speakers were pretty crappy anyway, much nicer for the end user to have a proper speaker with good sound quality to listen to.

Thanks everyone! This is really helpful. We are thinking that we should be able to plug them into an electrical supply with an extension cord, because there are several outlets in the area where they would be (for...some reason), but I'll look into batteries just in case that doesn't work out.

I've used PIR detectors, you put them inside of a toilet paper roll, and then they are directional, and much attenuated. Five, maybe six feet max.

Thanks everyone! This is really helpful. We are thinking that we should be able to plug them into an electrical supply with an extension cord, because there are several outlets in the area where they would be (for...some reason), but I'll look into batteries just in case that doesn't work out.

The batteries are not to be the source of the power. Thet are there to supply the proper voltage for the system I'd say I lean more towards gutting the entire system and putting everything new in low voltage use the highest quality speakers you possibly can

Use wall power if you can - batteries (of the modern day, 3.7V LiPo rechargeable variety - you'll have to plan on replacing the batteries every morning to be sure they last a day of continuous use so this has to be built to be easy and robust) if you must.

You will be able to replace the ear piece speaker if you can take apart the receiver. I think most of those were molded bakelite. Tough stuff, but doesn't play well. If the cover doesn't unscrew, try a dremel tool to cut it apart.

These DFPlayer mini MP3 players are easy to use and cheap on eBay etc. They can drive a small speaker directly. I think they should be loud enough, but get one to try.
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