I'm fairly new to this and I was wondering if it makes a difference if I put the current limiting resistor of a LED on the cathode or on the anode.  Any "best practice" and why?  Thanks!
35228
Please be kind, I am an electronics nub.  This is in reference to getting an LED to emit photons.  From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons flow from the more negative side to the more positive side.  In an example experiment (involving a primary dry cell, a SPDT switch, a resistor and an LED) it states that the resistor MUST be connected to the anode of the LED.  In my mind, if the electrons flow from negative to positive, wouldn't the electron flow run through the LED before the resistor; thereby making the resistor pointless?
39326
I now have a PCB with 64 UV LEDs on it and I use this to expose other PCBs. I have a serial resistor for each LED which produces a lot of heat and consumes about 1.3 A at 12 V.  I am now considering to make a bigger UV unit with twice the size of my current UV unit. I have searched on the internet how to drive this amount of LEDs but the only things I came across where ways to drive each LED individually.  I was thinking to make groups of LEDs (5 by example) and use one resister for each group of LEDs.  Are any other efficient ways to drive 128 LEDs without grouping the LEDs?
62375
I'm curious how much current it is safe to pass through a 0.1" pitch pin header. I'm sure it will depend on the gauge and stranding of the wire attached to it as well, but assuming that is not the limiting factor how much could be safely passed?
68213
I don't really understand how these diodes in this circuit and similar circuits (like driving a relay circuit) protects the controller circuit from the energy stored by the inductance of the coil. I really appreciate if someone could graphically explain it. ( I mean how the the diodes block the current and etc)  the second question about this circuit is the capacitor. what happens if it isn't there?
786
I've been looking over some board designs and have been trying to identify the reasons behind using resistor networks over individual resistors. Some guesses I can think of are a reduced part-count and complexity. Does it also follow that a design using a resistor network is cheaper than one that uses individual resistors? Because of this, I would think one would try to maximize use of networks, but many of the designs use several individual resistors instead and I can't figure out why.  And a separate but relevant question: are capacitor networks in the same boat?
43593
There are many tutorials that use a pull-up or pull-down resistor in conjunction with a switch to avoid a floating ground, e.g.        Many of these projects use a 10K resistor, merely remarking that it is a good value.  Given a a particular circuit, how do I determine the appropriate value for a pull-down resistor?  Can it be calculated, or is it best determined by experimentation?
92156
I've seen tutorials aimed at beginners suggest the way to drive an LED from something without enough current drive is this:   (option A)  but why not this:   (option B)  Option B seems to have some advantages over option A:   fewer components the transistor does not saturate, leading to a faster turn-off the base current is put to good use in the LED, instead of making the base resistor warm   and the advantages of option A seem to be few:   brings the load closer to the supply rail   but when Vcc is significantly greater than the forward voltage of the LED, this hardly matters. So, given these advantages, why would option A be preferred? Something I'm overlooking?
108780
I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it really matter here? These LEDs are working just fine without a resistor.
90117
This question is in regards to the EL817 Opto-coupler().  I'm trying to choose a suitable resistor to lower the current/resistor of the Opto's LED. With a source of 3.3v, an LED forward voltage of 1.2v at 20ma, I've calculated the resistor value to be 105ohms. Is this correct?
97571
I know this has been asked time and time again but bear with me as I am struggling to understand, so say I have this simple circuit here   with 120v (dc for simplicity) as the input voltage and I have an led that runs on 3.4v and max 20ma ohms law states I=V/R so R=V/I, so R=120v/0.02a = 6000 ohms or 6k is this correct? how do I know the voltage drop across the resistor is correct, and what about power dissipated by the resistor? also, Is there an easy way to calculate everything at once?
20834
For blue LEDs with a forward voltage of 3.3 V and supply voltage of 3.3 V, is a series resistor still needed to limit current?  Ohm's Law in this case says 0 &Omega;, but is this correct in practice?  Perhaps just a small value like 1 or 10 &Omega; just to be safe?
7517
I have an adjustable 24VDC power supply.  I have 1W LEDs that I was planning on stringing 7 or 8 in series to get approximately 24V across all of them together. They are rated 3.3-3.8V each. Do I need a resistor in series to maintain current? I was thinking so since a lit LED is basically a short? I can't find an answer to what it is really needed for, just that most people say to put a resistor in series to 'limit current'...  if so, it would be a small resistor, around 2 or 3 ohm?
6439
If we have this circuit:  The diode with the lowest forward voltage drop will conduct and turn on while the other will turn off and not conduct current. If I have this circuit:  Assuming the 2 diodes have the same voltage drop, R1 can be considered to be in parallel to R2 and that's how we solve those circuits. However in the same case, what if the 2 diodes have different forward voltage drops? Say Vd1&gt;Vd2 which assumption should I take into account?
118373
What’s the worst that can happen if i put a switch in the neutral instead of the phase?   I just found out that 3 light bulbs sockets in my home  are connected this way, it first came to my mind to fix it but then I recalled the flow of current from positive to negative is just a convention since the electrons are charged negatively and they actually flow from N to L so i cant really find an solid excuse to mess with the wiring for the next 2 hrs
25229
How can I have a LED either on or off (not in between) depending on night or day with basic electronics? I have created the circuit below, but it only shines and in darkness it dims.    The photo-resistor is about 3kΩ when light shines and about 1MΩ when dark.  I want my LED to shine at night and be off at day.  What is the simplest way I can achieve this?
26320
Shouldn't the current passing through a resistor be lesser than that which passes through a circuit? My understanding is that since Current = Charges/Time. If there exists a resistance to the flow of charges, then that must mean the charges slow down, meaning that more time is required to pass through a point. So, the current should then decrease. But, since this opposition to the flow of charges doesn't exist in the ENTIRE circuit, it should really only decrease the current in the resistor, right? Am I confusing the resistance of the resistor with the resistance of the wire? Any help will be appreciated! Thanks a bunch for lending me some of your time :D
76354
I'm struggling to understand the purpose of the resistor circled in red, I know it has something to do with DC biasing and the feedback on the circuit (as the capacitor will cause AC bypass). But I'm struggling to understand the exact circumstance where this would be needed. Is it a change in supply voltage, or change in transistor beta? And the exact mechanism that would cause the resistor to solve the problem.