galaxyrider
Posts: 33
Joined: Sat Dec 26, 2015 2:36 pm

Resistors and physical computing.

Sun Jan 24, 2016 6:26 am

Hello. I am an absolute beginner when it come to physical computing. I have just bought a RPi starter kit of electrical components from ebay. It has 220, 1k and 10k ohm resistors. Any of the LED projects I've seen use 330 ohm. Will it damage my Pi if I use the 220 ohm? Can anyone recommend a really good beginners site for to learn electronics, more especially breadboard. I have Googled but there are so many it's confusing. Thanks.

gordon77
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Re: Resistors and physical computing.

Sun Jan 24, 2016 7:15 am

No 220 ohms won't damage it, maybe a bit brighter. It may limit the number of leds you can light at once as the total limit from the GPIO's is quoted as 50 mA. You could put 2 in series for 440ohms, they will just be a little less bright.

If your led has a vf of 2v then
(3.3-2)/330 = 3.9mA,
(3.3-2)/220 = 5.9mA
(3.3-2)/440 = 3.0mA

Gordon

galaxyrider
Posts: 33
Joined: Sat Dec 26, 2015 2:36 pm

Re: Resistors and physical computing.

Mon Jan 25, 2016 6:05 am

Thank you for that. As I said I know absolutely nothing about electronics. If I wanted to buy some 330 ohm resistors for the Pi do I just search for 330 ohm or are there different types of them? I feel safer if I had what was recommended.
Thanks.

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rurwin
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Re: Resistors and physical computing.

Mon Jan 25, 2016 7:52 am

For lighting LEDs, any will do.

The other characteristics are the maximum power and the accuracy of the resistance. The smallest power you can get (unless you use surface-mount, which you are not) is an eighth of a watt.

20mA * 5V = 100mW = 1/10 W
5mA * 5V = 25mW = 1/40 W

So 1/8 W is plenty.

And you really don't care if your 330 ohm resistor is 20% out (+/- 66 ohms), which is the loosest accuracy. You're unlikely to find one these days anyway. 10% or 5% is more probable.

jahboater
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Re: Resistors and physical computing.

Mon Jan 25, 2016 8:31 am

Google "ohms law" or see the wikipedia entry - its actually very simple.

galaxyrider
Posts: 33
Joined: Sat Dec 26, 2015 2:36 pm

Re: Resistors and physical computing.

Mon Jan 25, 2016 9:07 am

Thank you all again. I have seen the +- on sites selling resistors. I'll definitely look at Wikipedia. I'm off to eBay to buy some 330 ohm resistors.

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electronicsguy
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Re: Resistors and physical computing.

Mon Jan 25, 2016 9:41 am

galaxyrider wrote:Hello. I am an absolute beginner when it come to physical computing. I have just bought a RPi starter kit of electrical components from ebay. It has 220, 1k and 10k ohm resistors. Any of the LED projects I've seen use 330 ohm. Will it damage my Pi if I use the 220 ohm? Can anyone recommend a really good beginners site for to learn electronics, more especially breadboard. I have Googled but there are so many it's confusing. Thanks.
Here's a link you could goto for some basic electronics with a breadboard: http://www.instructables.com/id/Ten-Bre ... Beginners/
blog: https://electronicsguy.wordpress.com
github: https://github.com/electronicsguy

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