**Experimental low cost versatile snake** The initial requirement was for a 4 channel audio extention lead (PA snake) for use in domestic room with 4 active loudspeakers (left, center, right and sub) at the opposite end of the room to the control amplifier (and rear speakers). Additional requirements to be added later were: 1. Balanced audio may be needed in electrically noisy environments. 2. A means of control signal could be used to individually turn the active speakers and TV off at the main supply (rather than just put into standby). 3. One cable if possible, and using connectors at either end rather than directly attached. Solution: Use HDMI flat cable, as it: - Has specified characteristics. - Suits consumer cost. - Is available at 10 meter lengths. - Contains 4 differential screened connections which would do for audio signals. - Has capacity for a (limited 5V at 50mA) power supply. - Contains connections for cable connection integrity check (send 5V back via HPD signal line to show plugged in). - Usefuly has couple of signal lines specified to carry an I2C channel for the cable length. - Has connectors at either end for easier cable re-routing, or replacing after damage, or decorating.... A later addition will have an add-on board connected by the FPC (on the underside) to use the I2C to drive an I/O expander such as an MCP23008 which could operate relays solid or mechanical (remember the 50mA cable spec. limit here, there will need to be additional local supply). There is also the CEC signal line that could be used for signalling, but unless you wrap it in a protocol or use async. timing (UART) or an analogue signal, it is going to be a bit limited. Anyway with a 3V3 pull up and open collector driver circuit (bit like an industrial rated 1-wire protocol driver) a CEC control project add-on could be made. More fun there then. Additional requirement: 1) Use this is a board for development of things using HDMI signals, plenty of room to put a mezzanine board on top! Notes: 1. DO NOT couple one end to a set of active speakers, and the other to a real HDMI source, this would put digital unipolar signals into an analogue signal chain; probable loss of tweeters and possible worse will ensue... 2. Ensure the 19 HDMI signal pins are aligned on the board pads BEFORE soldering all 4 of the HDMI connector shell mounting points, there will be a lot of heat-soak when trying to desolder the connector, and it may not survive. 3. Fix the phono/RCA connectors with the lower two plastic tabs on the board edge, not on top of the board, or by modifing the board with cut outs. The connectors will fit, but it's easier not to start by pushing the metal pins into the board pads, but line the tabs at board edge and rotate the connector into the board (or change the symbol and put cut-outs in your re-spin). 4. The signal lines are not length/impedanced matched for use on high frequencies, it may work with self-clocked data such as S/PDIF, although without correct termination it could be hit or miss. 5. The three-pin audio connectors are the most expensive parts here, if you don't want balanced signals, you may not want to fit them. 6. As with S/PDIF item; DMX signals have not been tried, but with cable length and the lower speed the 422/485 drivers may be forgiving. Also note this would be for the non-compliant 3-pin connector, and there is no 120R termination point (except a 1/4W resistor on the back of the connector between pins 2 & 3). 7. Ok disclaimer time: this is not an HDMI certified or compliant product (except for the licence cost on the connectors), additionally a note to that effect may prove useful to someone who is expecting it to be when it escapes from your workbench.