The γ3 high resolution DAC

Other options

Alternative I²S source

On the γ3 v1.01 backplane, under the footprint where the ζ1 Audio Widget USB-I²S module would normally sit, there are pads for a 5-pin extenal I²S input connector. If you don't use the ζ1, you could use another I²S source as an input to the γ3 DAC. It would be selected as input 0 on the remote control just as like a normal USB input.



This is the pin-out of that interface:
  1. GND - ground
  2. SCLK - the I²S bit clock
  3. DATA - the I²S data
  4. LRCK - the I²S word clock
  5. VCC - the logic level voltage
The first four pins are self-explanatory. The VCC pin is used to perform logic level shift, if necessary. Your I²S source must supply its logic level voltage into this pin. The allowable range is 3.3V to 5V. All voltages and I²S signals are referenced to the GND pin.

The external I²S wires should be kept as short as possible to avoid waveform degradation.

Alternative power relay

Instead of a solid state relay (SSR) as specified in the Parts list, you may use a "buffered" electro-mechanical relay module. The benefit of using such a module is lower cost, but it does increase the overall current draw on the LVDD power supply when in the "on" state.

There are several vendors that make or sell these relays, including amazon.com and ebay (search for "relay module 5V" and look for reasonable units). They are usually one or two electro-mechanical relays mounted on a small circuit board, with transistor drive. Some may have an opto-coupler input. You should choose one that's rated for 5V power supply operation, high-level trigger, with either one channel or two channels (SPST, SPDT, DPST or DPDT). With single-pole relays, you switch the "live" line of the AC mains just like how the SSR is usually wired. With double-pole relays, you can wire it such that the neutral line is also switched. With double-throw relays, wire your circuit in "normally open" configuration (i.e., contacts are open when untriggered).

These relay modules require an additional power supply and ground wire pair to the "always on" σ11.

The contact current rating should not be lower than 3A or greater than 10A. If the current rating is too low, the relay contacts may prematurely age. If the rating is too high, then chances are that it contains SSRs insread of electro-mechanical relays.

Here is an example 2-channel (DPDT) buffered relay, for 5V operation, and up to 10A of load current.



Note: Do not use an unbuffered, conventional electro-mechanical relay. The SSRTRIG output from LCDuino-1 does not have sufficient output current capability to drive a relay coil.


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