# Simple Circuit

Discussion in 'General Electronics Discussion' started by Zymus, Mar 31, 2010.

1. ### Zymus

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Mar 31, 2010
Hello, my name is Zyle, and I want to get into the world of circuitry and electronics. I know the basic equations, and have a brif grasp on the different purposes different components use, it's just the application i have a hard time with. So I thought that I'd start with something simple. A little LED circuit that switches between 2 LEDs with the help of an SPDT switch. I have a link for the diagram, and i was wondering if there were any special application techniques or methods that would make this, and all my future circuitry more efficient.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
That circuit seems perfect

Have you built this up? Do you have all the components? Do you have a solderless breadboard?

Do you own a multimeter? If not, I would encourage you to get one.

If you have one:

1) measure the voltage across the battery. Is it exactly the voltage you expect?

2) measure the voltage across one of the resistors when the LED it is connected to is turned on. What voltage is this? Use ohms law to determine the current passing through it.

3) Insert the multimeter in series with the battery using a current range. What current is drawn? Is it the same in either switch position? If not, why might that be so? Is it the same as you calculated from the voltage across the resistor?

If you do all that and can come to an understanding of why those readings are what they are, then you'll know more than some posters here.

Special question that is much harder:

4) What is the purpose of the resistors? What would happen if they were omitted? (hint -- DON'T try it)

Electronics is really great fun. It's amazing how much you can learn from a simple circuit like the one you have shown us.

3. ### Zymus

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Mar 31, 2010
I don't have the components as of yet, but i will be pruchasing them soon. I do have a breadboard. WIll i need to keep the SPDT switch away from the breadboard, or will it fit normally? I do have a multimeter, and i know how to measure ohms, amps, volts, etc with it. With the diagram, will i need both resistors? Or could i put the 140 ohm resistor before the SPDT switch, and then just wire the leds to that directly?

The purpose of resistors is to restrict the current. If you wire the LED directly to the battery or other power source, the current will be too high, and pretty much destroy the LED in the process.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
You can use the resistors either way. On the breadboard, instead of a switch, you can just use a jumper wire to link one of two parts of the circuit. It is unlikely the switch would fit into the breadboard, and if you used one it may be best to solder wires to it.

For jumper wires, I use the solid core wire from cat-5 cable. A metre of that cable will give you 8 metres of wire, which will last you almost a lifetime of breadboarding

Yes, that is why you need a resistor. If you look at a graph of voltage vs. current for a LED and a lamp, you'll see a significant difference.

All components have datasheets (some are harder to find than others, and some have more information than others) and reading these datasheets can tell you a lot about how the component behaves. These graphs don't tell the whole story, but they do illustrate that LEDs are not like light bulbs.

If you look at how lamps are specified, they typically talk about the voltage they operate at, for LEDs it is the current that they operate at. Loosely speaking, the series resistor changes a voltage source (a battery) into a current source (limited by the resistor). A resistor is actually a very poor choice if the battery voltage varies considerably, but for simple circuits (like yours) they are the normal choice.

5. ### Zymus

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Mar 31, 2010
Thanks for the information. Once i get the materials, i will surely be experimenting with various combinations of components. Do you happen to know anything about microcontroller programming or application?

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
If you are a beginner, I would point you at the Picaxe chip. It is very simple to program, and there is a lot of support for beginners. It also has a very low initial investment in programmers etc.

7. ### Zymus

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Mar 31, 2010
Cool, i'll check into it, thanks ^_^

8. ### Zymus

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Mar 31, 2010
One more thing, do the PICAXE chips have to be programmed in BASIC, or can they be programmed in C++?

9. ### 55pilot

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Feb 23, 2010
First, I do not recommend Basic. It is just too lame of a language and no one who has reached puberty should be using it I do not know why any prepubescent individual would want to use it either.

But if you are set on using Basic, check out the "Basic Stamp" series of devices. I have personally never used one, but they seem to be very popular and have fairly good reviews.

Steve keeps talking about this PICAXE. One of these days I need to figure out what it is.

---55p

10. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Picaxe's are programmed in basic.