Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: iCopyright_Everything on July 24, 2007, 06:04:00 PM

Title: RESISTOR BASICS - JUST TO CHECK!
Post by: iCopyright_Everything on July 24, 2007, 06:04:00 PM

Hi there!

Just to double-check, Resistors CAN have current flow in either direction through them, right?

By that I'm asking does is matter which way resistors are wired one end or the other, as long as they're in the right place....?

THANKS!

Title: Re: RESISTOR BASICS - JUST TO CHECK!
Post by: paulstreats on July 24, 2007, 06:20:32 PM

Ive always used resistors either way, and never had any trouble.
They are generally just a conductive material with non conductive impurities added so it is really just like a normal piece of wire, albeit with some resistance.

Title: Re: RESISTOR BASICS - JUST TO CHECK!
Post by: iCopyright_Everything on July 24, 2007, 06:29:08 PM

Great, thanks for the information, it's really good to know!

That's one down, (unknown) to go in my quest to figure out what the **** is wrong with my $50 Photovore circuit!

Ooh - follow up Question -- For an LED, what is a good value resistor to use to ensure the Microcontroller DOSN'T start being egg-fryable again!! --I have two values  from the tutorial -- 340 ohms AND 1.62 KILO ohms --- THE COLOR DOT SCHEMATIC  (here: http://www.societyofrobots.com/images/sbs_avr_schematic_small.png (http://www.societyofrobots.com/images/sbs_avr_schematic_small.png)) does NOT SPECIFY WHICH RESISTORS to use in Either the LEDs OR the Photoresistors!

Thanks!

Title: Re: RESISTOR BASICS - JUST TO CHECK!
Post by: airman00 on July 24, 2007, 06:50:43 PM

y would the microcontroller fry if it is providing the output. If anything the LED would fry

Title: Re: RESISTOR BASICS - JUST TO CHECK!
Post by: paulstreats on July 24, 2007, 06:53:16 PM

This is from the tutorial, i have highlighted the important part in red:-


The LED will be used as a status indicator. The LED is useful for knowing if your microcontroller is powered properly, and can output other useful information for testing purposes. A resistor wired in series is required so keep the LED from frying. Any resistor value from 10 ohm to 1 kohm will probably work. Higher resistance values reduce the power drain (good), but also decrease brightness (bad).  

---------------------------------

As lon as the resistors are in the right place, it wont matter.

Title: Re: RESISTOR BASICS - JUST TO CHECK!
Post by: iCopyright_Everything on July 24, 2007, 07:03:06 PM

Thanks guys!

(Sorry Airman I have no idea what you mean)

Title: Re: RESISTOR BASICS - JUST TO CHECK!
Post by: Admin on July 31, 2007, 07:16:14 AM

iCopyright_Everything, an LED is rated for a certain maximum power before it fries. Check its datasheet.

Power = voltage ^2 / resistance

So if power is 20mW, and voltage is 5 volts, use algebra to figure out the resistance.

I typically use a 100ohm or higher - it all depends on the LED and the brightness/efficiency I need.