The Power over Ethernet (PoE) is likely most suitable if the devices are network-aware, otherwise one Ethernet cable is pretty much equivalent to a (low current) power cord or a USB cable.
For any devices that to be "worn" or "attached" by test subjects, I would strongly consider an un-tethered design, powered using rechargeable batteries. For small signal (i.e. sensors, data logging, no motors, very simple LED lighting) this option should be easily economic and practical for up to 24 hour periods or longer. NiMH would be my first choice due to low cost and wide availability, with Lithium as a second. Just ensure you use an appropriate charger for the battery type, and things should just work.
Note that most rechargeable batteries such as 'AA' size cells, only provide 1.2 rather than 1.5 volts, so 4 of them is not sufficient for 5V needed to stably power an Arduino, while non-rechargeable (i.e. disposable) cells such as alkaline or zinc-carbon would.
With electricity you need to be aware of both voltage and current. The Arduino itself takes an input range of 7-12 DC, up to 500mA (I don't have a reference on average / typically current, but would guess around 100-125mA or less), from an external DC power source. The USB port can also be used to draw 5 volts, up to 500mA from a powered USB hub or powered USB port.
Using a low-cost low current (e.g. 250-500 mA output) AC-DC power adapter (wall wart) would be a default method if there is non-trivial power consumption, or needs to continuously operate for a long period of time.
A modern switch mode power supply (SMPS) based unit can be had for a modest cost, and is light weight, being able to dispense with the need for a large power transformer encased in it. Combined with the power limiting capabilities already included in the Aruino (UNO) from the resettable fuse (PTC, I believe) used for USB power source, and/or the linear voltage regulator used to regulate power from a AC-DC power adapter which also includes over-voltage, current limiting, and short circuit protection unless you need addition power requirements (e.g. motors, high power LEDs) you can use the protection built into the Arduino as sufficient for electrical shock/burn protection.
Looks like a cool project.
literal answer
The optoisolator is not necessary in this application.
Because you are generating the 100 V, 1000 Hz power to drive the EL from relatively isolated battery power (rather than mains power), there is much less of a safety issue.
Systems without an optoisolator typically connect the A1 pin of the triac is connected to the VCC of the microcontroller (in your case, the +3V supply), using "negative gate current triggering" as recommended.
A digital output pin on your microcontroller is connected with a resistor to the gate of a triac.
When the digital logic pulls the gate pin low (towards the microcontroller GND), the triac is triggered and turns all the way on.
As long as the triac is on, the A1 and A2 pins act like they are shorted together.
Turning the triac off is a little more difficult.
(A few systems without an optoisolator connect the A1 pin of the triac to the GND pin of the microcontroller, using "positive gate current triggering", which is not recommended.
As I recently learned,
hooking the the "GND" pin of the microcontroller to A1 and pulling the gate through a resistor to +3 V or even +5 V doesn't work right with a logic level triac.)
Try to draw your schematic and lay out your parts so it's obvious that:
- one end of the inverter output is solidly connected to a harmless-to-the-microcontroller voltage (probably +3V) and pin A1 of the triac
- the other end of the inverter output (the "hot side") is not directly or indirectly connected to anything anywhere near the microcontroller -- except for the triac, and even then the hot side is only indirectly connected through the EL wire to pin A2 of the triac.
alternate approach
If you're only going to have one strand of EL wire,
why don't you connect it directly to the inverter output,
and use a FET (rather than a triac) to connect and disconnect the inverter input to the +3 V power?
Best Answer
Very likely, the PoE injector has a current limit circuit to deal with a cable or device fault. For example, this Wikipedia article claims 350mA / 600mA limits for 802.3af and 802.3at Moreover, it seems that the limits are negotiated, so you could be set to an even lower limit.
The limiter would be there to protect the power supply and to ensure the continued operation of other devices that are powered by the same injector. And, more importantly, to protect against unsafe short circuit currents in the cabling which could, in the extreme, lead to a fire.