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Prototype VI - First Music!

Submitted by tylerjbrooks on Sun, 07/19/2009 - 23:03.

DigiSpeaker Prototype VI hit a major milestone this week. The Prototype VI Controller and Amp boards were able to play a WAV file!

Here is a picture of the two boards connected together. The Controller is on the left and the Amplifier is on the right. The AC cord coming from the upper left corner of the Controller card is connected to a powerstrip that has another powerline modem plugged into it. This provides the Controller card with its Ethernet link. The digital power supply is connected to the Controller card with the yellow cable. The orange cable is connecting +3.3V to the digital section of the Amplifier. Digital ground is connected to Amplifier board via the ribbon cables (about every other wire). However that digital ground is kept isolated from analog ground on the Amplifier (only connected at a single location -- as recommended by the DAC datasheet).

To play music, I wrote a three small programs. 'ampcmd' can be used to toggle the Amplifier control lines (reset and mute) and I2C registers. 'amptone' can be used to play square, triangle and sine waves. 'ampwave' can be used to play a WAV file. The source code for all three of these programs is attached.
Here is a picture of the amplifier. Two I2S signals from the Control board enter on the left through the ribbon cables. They are processed by the DAC (a TI PCM1690 on the left). The differential outputs of the DAC are then buffered and filtered by the two dual N5532s. This produces four outputs (two per I2S channel). The channels of the first I2S signal (left and right) are each fed into one side of the LM4765 for amplification. Likewise, the channels of the second I2S signal are fed into the second LM4765. However, in this case, the fourth channel is not used. Instead, the third channel is fed into both sides of the second LM4765. In this case, one side of the second LM4765 is non-inverting and the other is inverting. Speakers are then floated between the two amplifier outputs to create a BTL signal. This provides three channels of music that are intended for tweeter (30W), mid-range (30W) and woofer (60W).

Notice the large heatsinks connected to the two LM4765s. Those are actually fence building hardware that I found at Lowes and hacked up to make heatsinks for the amplifiers. Without them, the amplifiers went into thermal overload at very low power levels.

Here is a picture of the control board. This is not much different than previous posts. However, one significant difference is how the I2S channels are connected. In this case, Codec1 (PSC1) is used as the master I2S controller and Codec2 (PSC2) is in slave mode. Notice the wirewrap jumpers (in red) near the ribbon cables. This is where the bit-clock and the frame-clock of Codec1 is connected to their counterparts of Codec2.
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