Partially assembled Near Field Audio Speaker
Project data
Status Prototype
Made? Yes
Tools soldering iron, 3d printer
Uses Speaker, Near Field Audio Receiver
Download Open Know How Manifest
Page data
Type Project
Keywords Speaker, Near Field Audio, NFA, Near Field, Near Field Audio Speaker, Induction Speaker
Authors Harris Neill
Published 2021
License CC-BY-SA-4.0
Affiliations Michigan Tech Open Source Hardware Enterprise
Impact Number of views to this page. Views by admins and bots are not counted. Multiple views during the same session are counted as one. 95

The goal of this project is to design and create a portable speaker using Near Field Audio technology while maintaining good audio quality and a low cost BOM.

Background and Problem Statement[edit | edit source]

Most portable speakers operate wirelessly via the Bluetooth communication protocol. Near Field Audio is an alternative technology that sacrifices range for power efficiency and cost effectiveness. It also allows for device not compliant with Bluetooth to be used assuming they have a speaker output of their own. The goal of this project is to fill this niche with a quality, low cost, open source system.

Vision[edit | edit source]

To realize this Near Field Audio Speaker, the following goals need to be met

  • The project must be simple and have a low barrier to entry
  • Any parts used must be easily 3D printed or otherwise acquired
  • The cost to build the speaker must be $100 or less
  • The project must be open source

More abstract requirements were also defined:

  • Audio quality equal or better than comparable Bluetooth speaker
  • More efficient use of battery than comparable Bluetooth speaker
  • Inclusion of audio passthrough

Research and Design[edit | edit source]

To receive audio wirelessly a receiver is needed. With Near Field Audio (NFA) this is done via an electromagnet. In the case of this project, a 5mm in diameter 8mm length piece of soft iron was wrapped in ~4000 turns of 42 AWG enameled copper wire. While this was constructed, similar electromagnets can be found online for purchase. For it to function all that is needed is another speaker in very close vaccinty (less than 5 cm) to output its sound in a parallel fashion to the electromagnet.

The power of the signal the received is too low for direct audio reproduction though, meaning amplification is needed. Any digital audio amplifier should work here given it is properly powered. For this project a PAM8403 was used as it is low power and inexpensive. Any other digital audio amplifier should accomplish the same thing, but would have different power requirements thus requiring different parts for power delivery. Attaching the receiver to the input of the powered PAM8403 allows for greatly amplified audio playback.

The power requirements of the PAM8403 are quite small, only requiring a stable 5 V input. This was achieved via 3.7 V Li-Po battery and DC-DC boost regulator. Charging the battery is done via a Li-Po charging board fitting the requirements of the battery. For this project a MT3608 was used to charge the battery while a TP4056 was used to boost the voltage back to 5 V. Both parts were chosen for availability and low cost.

Of course to actually produce any sound a speaker is needed. In our case with the PAM8403 we are limited to two 3 W 4 Ohm speaker drivers if we want to access their full power. With the parts chosen here, the playback is substantially amplified with good audio quality.

Validation[edit | edit source]

As of now the only validation done is of general functionality. The speaker does indeed work as expected.

Future Development[edit | edit source]

This project is ongoing. The next five months present the following goals.

  • Perform more substantial testing versus competing speakers
  • Implement greater I/O for increased functionality

Bill Of Materials[edit | edit source]

To build a Near Field Audio Speaker of the same spec, the following parts are necessary:

Name Cost
PAM8403 $4
Pair of 3 W 4 Ohm Speaker Drivers $10
TP4056 $6
MT3608 $5
3.7 V 2200 mAh Li-Po battery $13
Equivalent Electromagnet $5
Total ~ $43

The price calculated here is a high estimate. All of these parts are cheaply available with the caveat of a longer shipping time.

Circuit Layout[edit | edit source]

To assemble, the following basic schematic can be followed.

Basic NFAS circuit layout

The connections are as follows for a similar parts list:

  • Li-Po Charging Board (TP4056)
    • Input should connect to 5V in, typically USB type power delivery.
    • Positive output connected to positive input on Battery and DC-DC Boost Board
    • Negative output connected to negative input on Battery and DC-DC Boost Board
  • DC-DC Boost Board
    • Positive output connected to positive input on Digital Audio Amplifier
    • Negative output connected to negative input on Digital Audio Amplifier
    • Optionally a capacitor can be attached between these lines for better audio playback
  • Digital Audio Amplifier
    • Assuming left and right input channel options on your digital audio amplifier and only one receiver, connect both left and right channels to one end of the magnetic coil and ground to the other end.
    • Left positive output connected to positive input on left speaker
    • Left negative output connected to negative input on left speaker
    • Right positive output connected to positive input on Right speaker
    • Right negative output connected to negative input on Right speaker

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