The military field phone is a rugged, reliable piece of equipment that has proven its worth throughout history. The problem with this old device though is lack of modern convenience: you need to plug the handset into a wall outlet, and it doesn’t have Bluetooth or any other wireless capabilities. Fortunately there’s an easy way around this issue: just turn the old school telephone into a Bluetooth compatible hands-free headset!
The Army’s Signal Corps employed the EE-8 Field Telephone from the start of World War II to the end of Vietnam. The portable ten-pound phones, which were carried in a leather (and later canvas and nylon) bag with a strap draped over the shoulder, supplanted the telegraph and flag signals as a more effective and efficient means for commanders and men to communicate on the battlefield. Two phones might be physically hooked together, or numerous phones could be connected to a common operator, allowing any phone in the group to communicate with any other phone in the group.
To notify another phone or the operator, a hand-generated crank on the phone’s side was cranked. The signal range between these tough, self-contained phones varied depending on the kind of wire used to link them and the circumstances in which the line was located (wet, dry, in the air, or on the ground), but it was normally about 11-17 miles. A direct, point-to-point copper wire connection, on the other hand, might increase the range to an incredible 360 miles.
The government’s excess EE-8s were sold to civilian homes after the war as a method for mom to summon dad out in the garage to inform him supper was ready.
Unless you have a pair or more, there isn’t much use for ancient field phones these days. While I like all things old, I’m not one for fetishizing antiques and demanding that they be kept on shelves or in the attic unless they’re really uncommon. Rather than merely admiring them, I like finding new ways to incorporate them into my everyday routine. So, with the aid of my electrical engineer brother-in-law, Ryan Davis, we decided to modernize the EE-8 by making it a Bluetooth headset that could be coupled with a smartphone or even a PC for VoIP conversations.
“Is there a functional purpose to do this, Brett?” you may be thinking. There isn’t any, sir. This project is all about having a good time experimenting.
But, unlike the ridiculously easy shoe shine box I showed you earlier this week, this project is not for the faint of heart. It requires intermediate soldering abilities and a basic understanding of circuits. This project will most likely take up to four hours to complete.
This is how you do it.
Requirements for Materials and Tools
- The EE-8 is a field phone. These may be found on eBay and at flea fairs. The cost varies depending on the age and condition of the item.
- Chip for Bluetooth headsets. We paid $10 at Bestbuy for a TurtleBeach Earforce PBT Bluetooth headset.
- This is a boost converter. For a few dollars, you can get it from Radio Shack.
- Wire. It’s just regular copper electrical wiring. Wire gauges of 26 and 30 were employed in this project.
- Iron for soldering
- Board with pegs
Unscrew the top of the Field Phone and remove it from its case.
To remove the field phone from the casing, first unscrew the screws on the side of the crank handle.
On the right, you’ll see a receiver switch. We’re going to take it off the top of the list. Also, notice the plate with the three wires protruding from it? We’ll get rid of it as well.
On the bottom of the receiver, there are two screws. Take them out and put them somewhere secure. We’ve already removed the left screw in this photo.
The receiver has been removed from the field phone’s top.
It’s now time to remove the top plate. Remove the right-hand screw.
There’s a screw in the shape of a pin. That, too, must be removed.
Change the receiver’s settings
If you’ve ever used a Bluetooth earpiece, you know that you push a little button on the earpiece to take or terminate a conversation. Our field phone’s receiver switch will take over the duties of the Bluetooth receiver’s button. We merely press the receiver switch once to accept a call on the field phone, and we tap it again to terminate a call. Isn’t it amazing?
In order for our Bluetooth tweak to function, Ryan had to tinker with the receiver switch a little. The receiver switch on a field phone is spring-loaded, meaning it depresses when the weight of the handset rests on it. The switch is open in this condition, and the EE-8 is turned off. When the handset is raised and the switch is closed, the EE-8 is turned on.
We required the switch to be open only if the phone wasn’t sitting on the receiver switch for our Bluetooth tweak to operate. Ryan did this by placing a piece of electrical tape between the plates to prevent them from making contact while the phone was not pressed against the switch. When the handset was sitting on the receiver switch, he soldered a ring around the plates to ensure that they made contact. A typically closed switch became an open switch as a result of this.
Ryan used duct tape between the plates and soldered a ring contact around them to change a typically closed switch into an open one.
Here’s a close-up of the soldered ring around the plates.
View of soldered switch plates from the top.
We’ll need to solder some fresh wire to the receiver switch’s soldering terminals. These wires will ultimately connect to the Bluetooth headset’s button contacts.
The receiver switch terminals from a different perspective.
On the top of the field phone, we placed some red and green panel LEDs. They’re not only amazing to look at, but they also have a purpose. When the bluetooth chip is in sync mode, they will alternate on and off, and the green light will blink when you get a phone call. Simply drill two 5/32″ holes and install the LEDs to complete the project.
The wires are pre-soldered on the panel LEDs. Each light should have one black and one red wire linked to it. The Bluetooth chip will ultimately be connected to these cables.
Connect new wires to the top plate’s terminals.
There are three terminals on the bottom of the top plate that we removed before. We replaced some worn-out cables with new ones since they were worn out. The handset’s speaker is controlled via the terminal on the left. Connect it to a green wire. The common terminal is the one in the center. Connect this wire to the ground (the negative battery terminal). The microphone on the handset is controlled via the terminal on the right. Connect it to a white wire.
The field phone has a terminal on top that connects to the batteries. Connect it to a new red wire.
Here’s a photo of all the new cables we installed recently. As illustrated above, thread them through the opening on top of the field phone.
Bluetooth Headset should be dismantled.
Remove the chip from your Bluetooth earpiece.
Out of the earpiece, this is what our Bluetooth chip looked like.
Connect the Bluetooth Chip to the Boost Converter
Have you seen the green rectangle next to the Bluetooth chip? A boost converter is what it is.
To operate, the Bluetooth chip needs a voltage range of 3.7 to 4.2 volts. The two DD batteries that power the field phone, on the other hand, only produce three volts. What can be done about the disparity in power? Boost converter is the answer. A boost converter takes the three volts from the battery and “boosts” it to the four volts the chip requires.
We mounted the Bluetooth chip and boost converter on a pegboard and used cables behind the pegboard to link the boost converter to the Bluetooth’s power supply. We chose 30 gauge wire since the soldering terminals on the Bluetooth chip are so tiny.
Connect the Bluetooth Chip to the Wires
The tough phase is about to begin. All of the cables from the field phone must be connected to various areas of the Bluetooth chip. Because each Bluetooth chip is unique, what we show you here may or may not work with other Bluetooth chips. You may need to use a scope to find out which terminals on your Bluetooth chip control the microphone, LEDs, speaker, and other functions.
We attached 30 gauge wire to the soldering sites first, then soldered the huge wires flowing from the phone to the 30 gauge wires, since the soldering terminals on the Bluetooth chip are so tiny.
Connect the wires from the receiver switch to the Bluetooth button.
Remember those new wires we attached to the receiver switch terminals on the field phone? We’ll need to connect them to the Bluetooth button in simultaneously. The field phone’s receiver switch will now perform the same functions as the Bluetooth earbud button.
Connect the LED Wires to the Bluetooth Device
The two black status LED wires must be connected to the Bluetooth chips. The boost converter will be linked to the red wires.
Connect the Microphone Cable to the Bluetooth Device
We had previously attached a white wire to the microphone connector on the field phone. That cable must be connected to the Bluetooth chip’s microphone-in terminal. The microphone-in terminal on our Bluetooth chip is on the back of the chip. Ryan attached 30 gauge wire to the chip terminal and then soldered the 30 gauge wire to the bigger, white wire since the soldering terminals on the chip are so tiny.
Connect the Speaker Wire to the Bluetooth Adapter and the Power Wire to the Boost Converter.
Connect the speaker cord (green) to the Bluetooth chip’s speaker out connection. It was on the other side of the button on our chip. The boost converter is connected to our power cable (red). The chip is connected to the ground line (black). Before connecting the wires to the Bluetooth terminals, we linked them with 30 gauge wire once more. The microphone cable (white) has previously been attached to the Bluetooth microphone connector.
Ground is the first wire. The second cable (green wire) connects to the Bluetooth speaker terminal. Ground is the third wire. Wire #4: Connects the output of the boost converter to the Bluetooth power input.
On the front, you can see how all the cables are connected.
And here’s how they seem from the back. Ryan said, “I utilized the pegboard as scaffolding for the two chips then wove and soldered wire to hold everything in place.” “It’s a little sloppy, but it did the job.” Ryan used double stick tape (the red rectangles) to prevent the wires from unplugging and to adhere the completed board to the interior of the EE-8 enclosure.
Replace the double D batteries in the field phone and replace the case.
Respectfully place DDs in the battery. Both positive ends must point upward. Return the field phone to its case. You’ve completed the task!
How to Use a Bluetooth Handset in a WWII Field Phone
Take out your phone! It’s a general summons!
Here’s how to utilize your WWII field phone using Bluetooth:
- Hold down the receiver until the red and green LEDs alternate on and off to put the field phone into sync mode.
- On your smartphone, choose Bluetooth device.
- When you get a call, the green LED will illuminate.
- To take a call, just touch the receiver once.
- To talk, press and hold the handset’s switch.
- Tap the receiver twice to stop the call.
- To make a phone call, just press the receiver once and dial the number on your smartphone.
Here’s a demonstration video: