Basic Circuitry Questions

Question

Hello, I recently began making circuits with Arduino Uno and I had a couple basic questions about the circuits I have made. 1) The first is that for all of the circuits I have put together, I am told to run a wire from the 5V power output to the side column of the breadboard. However, even when I unplug this wire the circuit still runs and seems as though the power doesn't have to be supplied. Is there already being power supplied through the output pins I have set up? 2) I understand that these circuits begin with the pin output and end with the ground. So I would think that if the led's needed a resistor, it would be before the led (on the side closer to the pin). This seems to be true for about half of the circuit diagrams I have seen, in several of the circuit diagrams the resistor is after the led. I attached pictures showing two diagrams showing each of these scenarios. Why is it different in these two cases? Why would the resistor be after the led? Thanks a lot 
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Former Member · Accepted Answer

Hi, So this is what I understood; you have arduino Uno connected to your breadboard, and you have the power pin connected to the breadboard. Having the 5V connected to the breadboard is required when the circuit is complicated (more components are connected in the breadboard that would need the 5V). From the pics you attached I could see your circuits are simple LEDs, if you connect the LED to PIN13 as it says, and you set PIN13 to High, then there will be current going through from the arduino to the LED (through PIN13) wether you connected the 5V pin to the breadboard or not. In regards to the second point mentioned, I agree with Bill, because the supply doesn't know if a resistor is connected first or not, it knows that there is a resistance in the circuit and it would allow current through based on the total resistance (R(total) = R1 + R(LED)) . Hope that helped.

billpenner · Answer

Hi Bill Here. With out the complete circuit I cannot be sure but; In the first circuit.. if you are using a USB to the computer, the USB probably supplies the power for the circuit. In the second circuit, Since both the LED and the resister are in series, all the current goes through both. So it makes no difference what is the order the components are connected. Bill

jw0752 · Answer

Hi Rick,

You have two good answers to your question but I thought that I might add that if you are looking for a book that has a good section on beginning electronics and circuit design you might want to check out "Practical Electronics for Inventors" by Paul Scherz and Simon Monk. There are three editions out. You can probably check out ebay if you want to save a little money. I would recommend the third edition as it has sections on microprocessors and interfacing with them. The earlier edition had a reputation of a lot of errata but the 3rd seems much improved. Good luck on you adventure in electronics.

John