This might be seem very simple to many of you, but I still get questions about simple microcontroller interfacing. So I will put a thread of notes about interfacing AVR microcontrollers to devices like LED’s, relays, I2C, etc.

As you might know Diodes require pretty small current. This current depends on diode type and can be from 3mA up to 20mA and more. Working voltage is from 1.5 to 4V.

One AVR pin can sink up to 20mA of current; it is convenient to connect diode directly to it with current limiting resistor. Never connect diode to pin without resistor – you may damage your AVR as your current may exceed the 20mA limit!

There are two ways to drive LED’s with AVR: sink and source. Sink method is better, because tour microcontroller doesn’t have to generate current to power LED’s. This may be critical when connecting more Diodes to AVR.

When connecting more than one diode, just remember that there is a maximum current that microcontroller can drive. For example Atmega8 maximum current can be 200mA.

The same situation is with opto-isolators as inside them there are the same diodes packed together with sensors. Optoisolators are convenient when you need to untie the controller from power circuits.

FYI: Current limiting resistor can be calculated very simply. Find out maximum current LED can handle and divide applied voltage by this current then you will have resistance of your resistor. R=5V/20mA=250Ohm. I usually double this resistance as I don’t like to drive my LED’s on maximum.

Blogsphere: TechnoratiFeedsterBloglines
Bookmark: Del.icio.usSpurlFurlSimpyBlinkDigg
RSS feed for comments on this post  |  TrackBack URI for this post

This entry was posted on Friday, May 12th, 2006 at 4:02 pm and is filed under AVR Microcontrollers. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.