Why is a MUTE command always issued at the end of each audio phrase in the example projects?

The KX1400 Audio Playback IC's built-in speaker driver will generate a constant (average) DC level when audio output is silent.  Because every speaker has some finite steady-state impedance, this DC output will cause power to be consumed in the speaker coil.   This wastes power (and can possibly damage the speaker).  To avoid wasting power in the speaker, a MUTE command should be sent to the KX1400 to turn off the speaker driver when the audio output is silent.

How can I prevent the faint, continuous tone I occasionally hear at the end of an audio phrase or Play Tone command?

Execute a MUTE command at the end of each audio phrase or tone sequence.

You should always execute a MUTE command at the end of an audio sequence to turn off the speaker driver.  This will (1) prevent the possibility of this unwanted tone, and (2) avoid wasting power by eliminating a potential DC bias across the speaker coil.  (See the FAQ above.)

Note: issuing a MUTE command via the MCU interface takes immediate effect.  You can avoid pre-empting a currently executing audio command by polling the state of the /BUSY signal.  See the KX1400 datasheet for details.

Why isn't a speaker included in the KX1400 Development Kit?

The KX1400 Audio Playback IC is designed to optimally drive a 0.25W 8Ω speaker.  However, the properties of a speaker (type, quality, size, enclosure, etc.) can have a significant impact on characteristics of the audio output.  The best solution for a speaker will vary greatly from one design to the next depending on the end application.  Since we are unable to anticipate the exact speaker required for your application, we thought it best to leave the speaker out, and keep the cost of the development kit low.

We highly recommended you select a speaker appropriate for your end application as early as possible in the design process and use it during the development of your audio content.  In the meantime, the KX1400 Evaluation Board is equipped with a 3.5mm (1/8" mini-plug) stereo audio jack to facilitate the use of a standard external PC speaker (powered or non-powered) or headphones during initial evaluation.

Why isn't Flash memory for audio content integrated within the KX1400 Audio Playback IC?

In most applications, the flexibility to select the memory size and configuration will lead to a system-level cost savings over a fixed-size, integrated memory solution.

The KX1400 allows you to choose the optimal memory size for your application's audio content.  Or, you can elect to utilize your system microcontroller's memory and use no external memory at all.  You don't pay for memory you don't need, nor are you forced to compromise on the design of your audio content to squeeze it into a fixed, " one-size-fits-all", integrated memory.

Why did Keterex develop its own USB-to-SPI Adapter?

As embedded systems designers, we have often needed a product like this, but have never found one with the features we needed at a reasonable price − features such as variable I/O levels and script execution.  This drove us to develop the USB-910H.

Why doesn't the Keterex USB-910H Embedded Systems Interface require user-installed device drivers?

We chose to use a USB communication protocol supported by device drivers pre-installed as part of almost all modern PC operating systems.  (The USB-910 uses the same device driver used by your USB keyboard and mouse.)  Although other forms of USB communications are faster, this method is sufficient for SPI and I2C operations and eliminates the risk of potential compatibility problems that can occur with user-installed third-party device drivers.

Are there plans to support the USB-910H Embedded Systems Interface under the Linux or Mac OS?

Yes, there are plans to port the USB-900 Control Center Application to Linux.  Contact support@keterex.com for current status and to let us know if you'd like to be notified when Linux support is added.  There are no plans to add support for the Mac OS at this time.

The KXUSB-150 documentation states it supports the USB 2.0 Full Speed data rate.    Does that imply it also supports the 480Mb/sec High Speed data rate?

No.  The KXUSB-150 Full Speed USB Isolator supports only the 12Mb/sec (Full Speed) data rate.  It does not support the Low Speed (1.5Mb/sec) or the High Speed (480Mb/sec) data rates.  However, it is compatible with any USB 2.0 host or device that supports the 12Mb/sec (Full Speed) data rate.