this is an arduino controlled relay/resistor (r/2r) attenuator ('volume control').
the lcd display (40x2) is controlled by a small arduino-like board (we call it the LCDuino-1) and its on the far left/front. there are 3 relay driver boards with i2c ribbon daisy-chain bus links. the relays are latching relays and each board controls 2 audio channels (usually a left/right pair).
what's new about this - for me and my project - is that its a trio - a hat-trick (lol) of volume control boards together ganged as a set.
on the front is a single volume knob that goes to a single gang linear motor-driven pot. that tells the arduino what volume level to set and then the right codes are sent via a flurry of i2c messages to the 3 controller boards. each controller board is a pair of i2c addr's and you write to each relay with a bit from each byte (pcf8574 PE chips). write a 0,1 and you bias the latcher one way; write a 1,0 and you flip it the other way. quickly write a 0,0 back to turn both relay 'wires' off to relax mode when the pulse is done.
this box is acting as a 3-band volume control for an active crossover. a single digital or analog signal is sent to a crossover and you get 3 analog outputs from that. those are the things that are fed into this box, with 3 outputs from *this* box going to 3 separate amplifiers, then each one going to its own speaker element (tweeter, midrange, woofer).
project will be opensource when coding is complete. boards will be available from amb.org (online) as DIY bare pc boards.
project info website (general): http://www.amb.org/forum/lcduino-system-f8/