The EE-8 Field Telephone was used by the Army’s Signal Corps shortly before the beginning of World War II and up through Vietnam. Carried in a leather (and then canvas and eventually nylon) case by a strap slung over the shoulder, the portable ten pound phones replaced the telegraph and flag signals as a more effective and efficient way for commanders and troops to keep in touch on the battlefield. Two phones could be wired together directly, or several phones could be connected to a common operator, which could put any one phone in contact with any other in the group.

A hand-generated crank on the side of the phone was turned in order to signal another phone or the operator. The signal range between these rugged, self-contained phones varied according to the type of wire used to connect them, and the conditions in which the wire was situated (wet, dry, in the air, or on the ground), but generally averaged about 11-17 miles. However, a direct, point-to-point connection made with copper wire could extend the range up to an astounding 360 miles.

After the war, the government’s glut of surplus EE-8’s were sold to civilian households as a way for mom to call dad out in the garage to tell him dinner was ready.

These days, there isn’t much use for old field phones, unless you have a pair or more. While I love all things vintage, unless they’re very rare, I’m not one for fetishizing antiques, insisting that they remain preserved on shelves or gathering dust in the attic. Rather than just looking at them, I love to find a way to put them to use again in my daily life. So with the help of my electrical engineer brother-in-law, Ryan Davis, we decided to mod the EE-8 for the modern age, turning it into a Bluetooth headset that could be paired with a smartphone or even your computer for VoIP calls.

You might be asking yourself, “Is there a functional reason to do this, Brett?” No sir, there is not. This project is about the pure fun of tinkering.

But bear in mind that unlike the incredibly simple shoe shine box I showed you this week, this project is not for the faint of heart. It requires moderate soldering skills and some rudimentary knowledge of electronics. All-in-all, this project will probably take up to four hours to accomplish.

Here’s how it’s done.

Materials & Tools Needed

EE-8 Field Phone. You can find these on eBay and flea markets. Price varies by age and condition.

You can find these on eBay and flea markets. Price varies by age and condition. Bluetooth headset chip. We bought an Earforce PBT Bluetooth headset by TurtleBeach for $10 at Bestbuy.

We bought an Earforce PBT Bluetooth headset by TurtleBeach for $10 at Bestbuy. Boost converter. Available at Radio Shack for a couple bucks.

Available at Radio Shack for a couple bucks. Wire. Just plain old copper electrical wire. We used a mixture of 26 and 30 gauge wire.

Just plain old copper electrical wire. We used a mixture of 26 and 30 gauge wire. Screwdriver

Soldering iron

Peg board

Remove the Field Phone from Its Case & Unscrew the Top

Mod the Receiver

If you’ve ever used a Bluetooth earpiece, you know that whenever you want to take or end a call, you press a small button on the earpiece. The receiver switch on our field phone will take on the functions that the button on the Bluetooth receiver had. To take a call on the field phone, we simply tap the receiver switch once; to end a call, we tap it again. Pretty cool, huh?

Ryan had to hack the receiver switch a bit in order for our Bluetooth mod to work. The field phone’s receiver switch is spring loaded so that it is depressed when the weight of the handset is rested on it. In this state, the switch is open, and the EE-8 is offline. The EE-8 comes online when the handset is lifted and the switch closes.

For our Bluetooth mod to work, we needed the switch to be open only if the handset wasn’t resting on the receiver switch. To do that, Ryan put a piece of electrical tape between the plates to keep them from making contact with each other when the handset was not resting on the switch. He soldered a ring around the plates so that they made contact when the handset was resting on the receiver switch. This turned a normally closed switch into an open switch.

Add LEDs

Connect New Wires to Terminals on Top Plate

Dismantle Bluetooth Headset

Connect Boost Converter to Bluetooth Chip

The Bluetooth chip requires a range of 3.7 to 4.2 volts of electricity to power up. However, the two DD batteries that power the field phone only put out three volts. What to do about this power gap? Answer: boost converter. A boost converter takes the three volts from the battery and “boosts” it up a voltage level so the chip gets the four volts that it needs.

We placed the Bluetooth chip and boost converter on a pegboard and connected the boost converter to the Bluetooth’s power source with wires behind the pegboard. Because the soldering terminals on the Bluetooth chip are so small, we used 30 gauge wire.

Connect Wires to Bluetooth Chip

Now comes the tricky part. We need to connect all the wires from the field phone to different parts of the Bluetooth chip. Every Bluetooth chip is different, so what we show you here might not work on other Bluetooth chips. You may have to use a scope to figure out which terminals on your Bluetooth chip are responsible for the microphone/LEDs/speaker/etc.

Again, because the soldering terminals are so small on the Bluetooth chip, we soldered 30 gauge wire to the soldering points first and then soldered the big wires running from the phone to the 30 gauge wires.

Connect Receiver Switch Wires to Bluetooth Button

Connect LED Wires to Bluetooth

Connect the Microphone Wire to Bluetooth

Connect Speaker Wire to Bluetooth & Connect Power Wire to Boost Converter

Insert Double D Batteries and Put Field Phone Back in Case

How to Use Your WWII Field Phone Bluetooth Handset

Here’s how to use your Bluetooth WWII field phone:

Put field phone into sync mode by holding down receiver until red and green LEDs begin alternating on and off.

Select bluetooth device on your smartphone.

When you get a call, green LED will light up.

To answer call, tap receiver once.

To speak, push and hold switch on handset.

To end call, tap receiver twice.

If you want to make a call out, you’ll have to tap receiver once and dial number on your smartphone.

Here’s a video of it in action: