I was looking for a fun project for my Raspberry Pi, and decided a case would be fun. I found an old rotary phone and converted it into a case for my Pi. I needed about $40 worth of parts, you might be able to do it for less. The whole project took me about 4 hours of planning, and about 6 hours to assemble.
The best feature: It powers on when you remove the handset, and powers off when you place it back into the cradle. Granted, it is not a graceful shutdown, but for most purposes this is fine.
Step 1: Parts List
Before you start: Please assess your rotary phone and plan where the components will go. Depending upon the size of the USB hub and the position of its external power connector, it may not fit, or it may interfere with other parts. Take your time and plan ahead so that your project is a success.
Here are the parts used for this project, and the reasons you need them.
- An old rotary phone
- This will be gutted and used to house everything.
- A Raspberry Pi
- You'll need a small case for it, although only the bottom tray will be used.
- A powered USB hub
- The Pi is famous for low power consumption, with little to spare, so any accessories should attach via a powered USB hub.
- I salvaged an old Staples branded hub, and removed the board from it.
- Note the type of power connector used. Mine is a 3.5mm.
- Connects the Pi to the USB hub.
- 90 degree is good for tight spaces.
- Amazon: 90 Degree Angle Micro USB Cables, VANDESAIL 2 Pack USB 2.0 A Charging Data Sync Cable for Fire TV Stick, Power Bank, Chromecast (1ft, Right Angle + Left Angle)
- Provides a female jack you can plug the USB hub power transformer into.
- Amazon: TOTOT 12 Pack 3.5mm x 1.3mm 2 Pin Female DC Power Jack Panel Mount Screw Nut Kit DC Socket Electrical Plug
- Your USB hub power will be supplied outside the phone, into the DC power jack (above).
- This cord will connect from the inside of the DC power jack, and deliver power to the USB hub.
- Your Raspberry Pi takes power from a micro USB cable.
- This adapter allows you to plug that power into the back of the phone, and deliver power to your Pi.
- Amazon: CGTime (30cm) Micro USB Panel Mount Cable, Micro USB Male to Micro Female Ear Screw Install the pane Data Extension Cable, Sync Charging and Data Transferring Cable (Micro USB)
- Allows you to "move" the HDMI port from your Pi to the back of the phone.
- Amazon: AFUNTA HDMI A 1.4 19pin Male to HDMI A Type Female Extension Cable with Screw Hole 30cm Can Lock Panel Mount Cable
Support tools and consumables:
- Soldering gun and solder
- Shrink tubing and heat gun
- Electrical tape
- Dremel tool
- Small file set
- Drill and bits
- Painter's tape
- USB hub mounting hardware (scrap pipe hanging strap works great)
- Wire cutters and strippers
- Multimeter (need to read ohms and DC volts)
Step 2: Disassemble and Gut the Phone
My phone had 2 screws in the bottom. Unscrew those and the cover comes right off.
There is a ringer assembly that is held in place by 2 screws. Disconnect all the wiring, remove the screws, and then remove the ringer assembly.
My phone had another small circuit board held in place by a gray plastic holder. After removing that board from the holder, I used a Dremel tool to grind off the rivets from the underside of the phone. The holder came out easily.
Step 3: Cut the Holes for the USB Hub Ports
The USB hub attaches from the underside of the phone at an angle, and the ports are accessible from the curved area behind the handset. One way to cut these holes:
- Place painter's tape on the back surface.
- Dab some lipstick onto the rectangular USB ports.
- Press the ports onto the tape to leave marks. Clean the ports with rubbing alcohol and a paper towel.
- Use a Dremel tool with a cutter (see 194 1/8" High Speed Cutters). This is useful for gouging the plastic, and I found that medium speed with some pressure actually melted the plastic away.
- Use a small file set to clean up the holes. You can hold the board from behind to assess where to file. A cheap set from Harbor Freight works well (see Precision Needle File Set 12 Pc).
Step 4: Mount the USB Hub
From the inside of the phone case, position the USB hub circuit board.
I created 2 brackets by using small pieces of pipe hanging strap, bent so its holes align with the circuit board's holes. This will take some effort to measure and cut properly. The brackets are then epoxied into place.
Once the epoxy has cured, place small pieces of electrical tape on both sides of the board where it makes contact with the brackets. This will prevent short circuiting.
At this time, you should check the fit of the 90 degree micro USB to USB-A connector. This attaches the hub to the Pi, and depending upon your USB hub, this might be a tight fit. I had to grind away some of the phone case interior as well as the 90 degree connector's rubber material.
Then attach the board to the brackets with small screws and nuts.
Step 5: Attach the Micro USB Back Panel Port to Power the Pi
Similar to the method used for the USB ports, cut a hole in the back of the phone to accept the micro USB panel mount port. For a flush mount, I used a razor and cut away the raised lobes so that the part fit flush against the interior of the phone case. Mount with 2 screws. The other end of the cable will (eventually) go to the Pi.
Step 6: Install DC Jack for USB Hub Power, and Connect to USB Hub
Drill a hole in the back of the phone to accept the DC jack for the USB hub. Install the fitting and secure into place with the provided nut.
On the inside, you'll have to use a scrap power plug to connect from the back of the DC jack to the USB hub. I had a spare 2.5mm plug, which I cut and attached crimp connectors. Attach this "cheater" to the back of the DC jack and then to the USB hub. Check the polarity by plugging in a USB device with a light and briefly applying power through the jack.
Step 7: Install the HDMI Panel Mount
I was able to find a location between the USB ports and the handset. Using the tried and true method for the USB hub, mark the location of the HDMI port and cut/file the plastic away. Mount using the provided screws.
Step 8: Install the Fan
The fan I ordered is a USB fan, which means it plugs into a USB port and runs off the 5 volts provided. The fan was pretty loud, so I decided to wire it to run off 3 volts instead.
To do this, I cut the fan's USB wire and found the red and black power wires. Since I didn't have a nice connector, I ended up stripping about half an inch of insulation away and securing to GPIO pins 1 and 6 with heat shrink tubing. Be sure to check the polarity first.
My fan is set up to pull in air from the underside.
Step 9: Install the Hook Power Switch (optional)
You could power up the phone by plugging in the micro USB and USB hub power, but I wanted something more: power on by lifting the handset.
To do this, you need to interrupt the power in the micro USB to USB-A cable (this accepts power from the back and delivers it to the Pi). Here are the steps I performed:
- Determine which hook wires complete the circuit when the handset is lifted. This takes some trial and error, but eventually you'll find 2 wires that provide a closed circuit when the handset is lifted, and an open circuit when the handset is in the cradle. Use an ohm meter to test this.
- Cut the micro USB to USB A cable. Strip back the outer sheath, cut away the shielding wires and the foil, and access the wires inside.
- You don't care about the green, white, and bare wire, so fold them back and secure with heat shrink tubing.
- Solder the black wires together and shrink tube the joint.
- Connect one red wire to one hook wire identified above, and the other to the other hook wire. Shrink tube the joints.
- Since the assembly felt fragile, I bound the thick USB cables with electrical tape.
Step 10: Stuff Everything Inside and Test It Out!
Along the way, you should have been checking for fit and planning cable management. I used hot glue in a couple places to secure wiring and keep things from getting pinched or interfering with the hook. You should also be confirming your connections and testing power and function.
My Raspberry Pi came with a small case. I removed all but the bottom tray, and with the Pi in that tray, found it wedged nicely (see pic). The tray protects the Pi and also keeps it from shorting out on the metal phone base.
Once assembled, you simply connect the HDMI, both powers (micro USB for the PI and the DC for the USB hub), and any USB accessories such as a keyboard, mouse, or game controller. Turn on your TV, and then lift the handset.