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  • Labs project

2.4 GHz wireless digital headphone (Texas Purepath)

Status: Proposal
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August 29, 2014
PS3B.JPG

The project is based on the Texas CC8520 Purepath Technology through the A8520E24A91 ANAREN module which integrates a CC8520 and a RF amplifier CC2591.

The receiver (PS), although an ANAREN module is a transceiver, operates in the "hosted mode" to allow future functionality, thanks to the data channel, like remote control from the transmitter, channel selection, ... It's powered with a USB power bank.

The PIC 18F2550 (bottom side) acts also as a USB loader (as the Texas CC Debugger) to prgram the ANAREN with the *.hex generated by the Texas "Configurator" software.

See the synoptic PDF.

The sound quality is (very) good. In free field and with the transmitter in height, 75 m are achieved. The audio flux is PCM 16. To enhance the strength of the wireless audio link, an almost inaudible SLAC compression can be activated on the transmitter side, the receiver will follow.

An adjustable limiter can avoid to hurt the ears.

MUSE capacitors are used on the audio path.

In spite of efforts (especially galvanic isolation between the digital and the analog circuitry - see synoptic), a small noise of digital origin can be hear. Please, help! More copper on my PCB ? Ferrite bead ?

When the stereo signal is taken just after the CNA (CS4334, bottom side) to be sent to an HIFI amplifier, the noise becomes negligible.

Instead of a wireless headphone application, this electronic architecture can be used for sound reinforcement. The latency is 20 ms max.

The transmitter (PM) side is on a "Protoboard". The CAN is a WOLFSON WM8783. The .HEX was loading in the ANAREN thanks to a PIC18 and a FTDI USB serial cable.

The PCB of the receiver is formatted to accommodate in a low cost HAMMOND 1553C box.

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Images
Receiver, shielded box (analog circuitry) closed
Receiver, shielded box (analog circuitry) opened
Schematics

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