ok. i get it. in the first circuit the resistors are in parallel, so the overall resistance is less than 330 Ohms (without getting into the math or anything) so the first circuit will draw more power.right?Wrong, the first circuit has three independent series circuit, all they share is the power and ground. In each circuit, each led is limited by it's own resistor. So the three led/resistor series CIRCUITS are in parallel, not the three RESISTORS. To say it differently, if you changed the value of just one of the resistors in that first circuit only one led's brightness would change, the other two leds would remain the same brightness as before. Therefore they aren't acting as a single parallel circuit, but rather three independent circuits wired to a single power supply.So in order for the circuits to be equivalent I would need to use higher value resistors in the first circuit, or a lower resistance in the second.The two circuits are fundamentally different, regardless of the size of the resistor(s) used. However, yes, if you wanted all the leds in both circuits to have the same brightness you would either have to increase all three resistors size used in the first circuit or lower the one resistor size used in the second circuit. *ok, so another scenario:I hook up one of these sensors + breakoutboard to my arduino: http://www.sparkfun.com/products/9453The board includes an IR LED with an 100 Ohm resistor attached. As its only one sensors+board everything is ok.If I however take say, 10 of these sensors, and hook them all up to the same powersource/ground, then I have a problem, becouse the overall current increases, as the resistors are now in parallel. Correct?No, The total current drawn from the power supply would increase only because there are 10 independent series sensor/resistor circuits all consuming current at the same time. Resistors only are considered being in parallel if both their leads are wired together (at both ends), two 10 ohm resistors wired in true parallel end up having a real resistance value of 5 ohms. Your first led circuit example has the three resistors wired together only at one end, so they are not acting as a single resistor, but rather as three independent current paths. Total circuit current is the total of each branch circuit. (concidentally there is no way of increasing resistance on these boards without decreasing the resolution of the sensor output --- stupid design --- but anyway thats not the point.)
so in order for the circuits to be equivilant I would need to use higher value resistors in the first circuit, or a lower resistance in the second.
I use this website: ... to calculate LED resistor values. It has options for calculating the proper resistor for either of your option (1) or (2).
I usually construct circuits on a more or less trial and error basis...
There are probably others. It would be interesting to see where Arduinos and clones are advertised most.
I am beginning to understand that "it works" is very relative