Eli with Bluetooth Technology

The ELI DirX Ear-Level Instrument (Figure 1) is the smallest audio Bluetooth device on the market, with dimensions of 27 mm x 16 mm x 11 mm and a weight of 5.2 grams. Three pins connect it to any behind-the-ear hearing aid that uses a Europlug standard direct audio input (DAI) connector (Figure 2). The pins on the ELI DirX module rotate 270 degrees to accommodate either a right or left hearing aid.

 

ELI DirX provides bidirectional digital communication between a Bluetooth-enabled mobile phone and a hearing aid. Since the signal being transmitted between these devices is digital, it is not subject to the same sources of interference as other types of wireless transmission, such as analog FM or analog inductive transmission.

 

In this Bluetooth application, the ELI DirX module is the slave, while the mobile phone with which it communicates is the master device. To pair ELI DirX to a mobile phone or other Bluetooth master, the user holds down the button on the ELI DirX module when it is within 10 meters of the other device. The light emitting diode (LED) of the ELI DirX module blinks red and green, indicating that it is in the pairing mode and then glows a steady green when pairing is complete. Connecting is accomplished by clicking icons on the mobile phone screen, and reconnecting is as simple as pressing a button on the ELI DirX module or clicking icons on the mobile phone.

 

The ELI DirX module is very easy to use. When a call comes in, it rings through the hearing aid itself via the ELI DirX module, instead of ringing from the phone. To answer, the wearer simply presses the button on the ELI DirX module. If the caller hangs up, ELI DirX recognizes that the call is finished and disconnects automatically. Alternatively, if the wearer wishes to hang up, he or she can do so by pressing the ELI DirX module button. One needs the mobile phone only to dial.

 

During a phone conversation, the digital voice signal from the mobile phone is transmitted via Bluetooth to the ELI DirX module. The module converts the digital signal into its analog equivalent and sends the resulting electrical signal to the hearing aid circuitry via the DAI boot. When a signal from ELI DirX enters the hearing aid through the DAI boot, it overrides the microphone signal and is shaped by the same parameters that govern the hearing aid response for a microphone input. Thus the response characteristics are well customized to the hearing aid wearer's needs.

 

A microphone on the bottom of the ELI DirX module picks up the wearer's voice. ELI DirX performs an analog-to-digital conversion and sends the resulting digital signal to the mobile phone via Bluetooth. The proximity of the microphone to the speaker's mouth ensures a strong signal level and favorable signal-to-noise ratio.

 

The ELI DirX module is powered by a custom, rechargeable lithium-ion-polymer battery, which is fully recharged in 1.5 hours by placing the module in its charge cradle (Figure 3). Since talk time on such a device is a critical variable, considerable effort went into the battery development. Active talk time of the ELI DirX module is 2.5 hours, and at full charge the battery has a standby life of 140 hours before recharging is required.

 

The ELI DirX module relies entirely on its own power source and does not drain current from the hearing aid battery. Therefore, it has no impact on hearing aid battery life.

 

The strength of the mobile phone audio signal at the wearer's ear is determined by the settings of the mobile phone and the hearing aid. If the wearer wants a louder signal, he can adjust either the mobile phone volume or the hearing aid volume.

 

For hearing aids that have a telecoil but no DAI capability, an alternative coupling for the ELI DirX module has been developed. For this application, the module attaches to a custom Adapted Neck Loop through a specialized ELI DirX connector (Figure 4). This alternative inductive coupling is especially important for the large number of wearers of custom hearing aids with telecoils, which are not compatible with the Europlug connector.