I would like to use an Arduino to control the current (Amps) delivered to the LED.
As you can see in the attached picture or in the product page, the most right trimpot controls the current, so I'll have to connect the Arduino to it.
BTW, I'm using the same battery pack for the Arduino and the Driver (8.4v Lithium), though it seems that none of the trimpot terminals connect to positive on the battery.
So if I want to control that, what so I do or use? Maybe a transistor through the analog pin?
It looks like the unit is potted, that is encapsulated in resin. There is no way to tap into the controls so I think it is not possible to do this without smashing those pots and trying to connect to them.
There is no electrical connection you can get at as far as I can see from the photo. The ends of the trim pot are encapsulated. Do you mean attach a small motor onto the trim pot to turn it under arduino control?
Right, that's not what it looked like on the Ebay picture.
If as you say the trim pots do not connect to the positive supply and that trim pot is connected as a variable resistor (wiper tied to one end) you need to measure the voltage on both pins with respect to ground. If this doesn't exceed 5V then you are in luck and it is relatively straight forward. You need to use a digital pot:-
because the circuit is using the current through this pot to generate a control voltage so you can't just inject a voltage at this point.
If it does exceed 5V you still need a digital pot but one that takes the extra voltage, this is a different one than is shown in this tutorial.
Well, I measured about 150 millivolts while battery and LED are connected
It seems incorrect
I was expecting two readings, between the battery negative and each one of the pot leads. Did you have it running current into a load when you did the measurements? A low value resistor will do.
could I use a phototransitor?
No, even an LDR would give you very non linear results (see another current thread on this) like going over most of the range for only one difference in the PWM (analog output)
