# My First Post, and with Questions =D

Discussion in 'General Electronics Chat' started by AgentSmithers, Jan 14, 2011.

1. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
62
0
Alright, Well I'm glad to have join this forum, I've been a major Visual Basic Junkie for about 6 years now and I'm moving into the Physical work now =)

I have a Goal set, and My question is now that I have an Idea, I need to start buying my parts to experiment with building a Circuit. What parts does every circuit builder need and I got a couple starter kits that let me use a Microcontroller to build a basically switch to turn on and off a LED but in between the two I need a resistor, but How do I know which one do I need to use, do I need to locate the part on the internet and then figure out my incoming voltage and use a resistor to drop the voltage down to something the led can handle? I got a grip load of parts here but I have no idea what i need to put inbetween them to ensure I don't overload them and burn any of them out, Current I have a 9v Battery as a powersuppy on a small 10x16 breadboard.

Thanks!

2. ### tom66 Senior Member

May 9, 2009
2,613
218
Hi, welcome to AAC

Working out the resistor for an LED is quite simple.

You need to know three main parameters:
- your supply voltage (Vs) (e.g. a 9V battery)
- your LED's forward voltage (Vf) (1.2V-1.5V for infra-red, 1.8V-2.5V for red, some green and yellow; 3V+ for other green, blue and white LEDs. Check the datasheet or website - it's usually specified.)
- the desired LED current (If) (For small LEDs, in the range of 15mA to 30mA. Higher is brighter, but uses more power. If you go too high, the LED may overheat and burn out. If you're driving bigger LEDs, it may be in the range of 50mA to 100mA.)

Then the formula is quite simple: (Vs - Vf) / If. So given 9V, a 2.2V red LED and a desired 20mA forward current, we get: 340 ohms. Now that isn't a standard value. The standard values are 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8 and 8.2, including all multiples of 10. It turns out that 330 ohms is standard and close enough to 340, so you can use that.

Oct 29, 2009
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4. ### Wendy Moderator

Mar 24, 2008
21,291
2,904
I have a article on how to calculate them for yourself.

Chapters 1 and 2,

LEDs, 555s, Flashers, and Light Chasers

Many online calculators have hidden pitfalls, because they lack common sense they will will blithely give answers that flat don't work in borderline cases.

5. ### maxpower097 Well-Known Member

Feb 20, 2009
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Last edited: Jan 16, 2011
6. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
62
0

Well Not just for LED but for any part, do I have to hunt down the Manufacture and find the model and look for its current range?

7. ### tom66 Senior Member

May 9, 2009
2,613
218
Well what type of device? If you're talking about a complicated device which depends on a stable voltage, a resistor is not the way to go. But if you want to just run a small component, a resistor will probably work. You need to specify what you want to do.

8. ### maxpower097 Well-Known Member

Feb 20, 2009
795
393
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Last edited: Jan 16, 2011
9. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
62
0
Gotcha, But I want to start getting into 802.11 programming, where should I start? I've done the basic LED Bulb's with a microcontroller, where a good goal in the middle to target next?

10. ### tom66 Senior Member

May 9, 2009
2,613
218
LEDs aren't bulbs because they don't have filaments.

A good place to start is an intermediate project which can be combined with your final project but also has a functional use on its own. You want to use 802.11 - but what data will you send? If, for example, you are sending temperature data, design a temperature sensor which outputs the temperature on a display or on the LEDs.

11. ### SgtWookie Expert

Jul 17, 2007
22,202
1,788
Please do not ever suggest that "wizard" again.

It will often give bogus results.

Last edited: Jan 14, 2011
12. ### AgentSmithers Thread Starter Active Member

Jan 14, 2011
62
0
How about maybe starting with a RJ45 Connection, What parts should I get to start sending and transmitting data from a Basic stamp homework board, I figure that is something that I can easly work with cause I'm Network+ certified so It will aid me in the project. Any idea's, Thank you everyone for your help!

Would this work?
http://microcontrollershop.com/product_info.php?products_id=3463

Last edited: Jan 15, 2011
13. ### maxpower097 Well-Known Member

Feb 20, 2009
795
393
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Last edited: Jan 16, 2011
14. ### tom66 Senior Member

May 9, 2009
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Could you point out any examples? It (and the formula it uses) is usually good enough for small LEDs. I've used it successfully.