Ingredients:
* Vintage payphone replica ($69 @ walmart.com, but I had one lying around)
* RPi ($30ish?, but I had one lying around)
* VOIP adapter ($30ish?, but I had one lying around)
* 12V to 5V 10A stepdown converter / voltage reducer ($15 @ superbrightleds)
* 12V UPS battery (will a 6V work?) (had one lying around)
* Alternately, an Anker powercore will eliminate the need for a stepdown converter and possibly run the whole thing.
As you can see, there’s a good amount of room, but some creativity will be required, as a lot of that room is taken up by the coin chute. Do I care if the coin shut works? Probably not. I could either squeeze the components (boards only, no housings) in around the coin chute or cut the coin chute out to fit way more components.
It’s clear the UPS battery from the original plan isn’t going to fit. Maybe an Anker power core with 3A ports. By my calcs, that should run the unit with no external power for at least around three hours.
I’m also considering cutting out the area where the instruction card currently sits and adding a touchscreen. The 3.5 TFT screen for Pi only uses another 100ma. Chump change.
This is the Cisco 3102 motherboard without its housing. I’ve tried to find a smaller profile option, but have so far been unsuccessful. There are USB FXO devices out there, but Linux support tends to be lacking, much less the specific ARM platform support required by the Pi. Forums continue to redirect back to the SPA3102, mainly because it’s quite affordable. At about 4″x4″, there are plenty of places it will fit within the payphone housing.
OK. Found a better stepdown converter. Really nice profile. Also, the UPS battery fits PERFECTLY where the change collects. So I’m thinking if I cut the coin chute short a bit and add another collection tray up top, I could still collect money. And even though this battery is undercharged, and registers just over 9V, it’s still providing 5V on the output of the stepdown converter.
Next step: Connect components and see how long they run on battery power. Connector for SPA3102 on order, should be here late this week. I’ll use the downtime to configure a Pi build that is safe as far as power loss (meaning, read-only file systems).