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Per Westermark
01/02/12 08:50
Read: 459 times

#185260 - Sink or source? Does matter a lot!
Responding to: ???'s previous message
Adam Collins said:
30 years?that's older than me lol. Yeah I agree. And Thanks but can I ask quick unrelated to at89s52 but more to circuits. I used a code to make a LED on P3.0 pin to illuminate every 1 sec it works but with low intensity any way to increase it?( I remember we had to use resistor but what's the value?)

You take lots of things for granted - or ignores it - with that question.

A LED can be connected in more than one way.

Depending on used processor, you'll have different capabilities when LED is connected between + and pin or between pin and ground. Most processors are way better to sink current (i.e. the LED connected with series resistor to VDD) than it is to source current.

Only some newer/more advanced 8051 chips have configurations to allow the chip to modify the pin drive logic so it will be able to source current - where the chip internally has a transistor between VDD and the pin. So a traditional 8051 design always sinks current - uses the internal transistor from the pin to ground.

Size of resistor? That depends on many things. The amount of current the LED supports. How bright you want the LED (which also includes the efficiency of the LED). But also the maximum currents the processor pin supports. And the maximum power dissipation allowed on the processor port. And the maximum power dissipation on the full processor.

List of 32 messages in thread
AT89S52 and ISP problem      Adam Collins      01/01/12 13:38      
   Quick Schematic Obversation      Michael Karas      01/01/12 18:28      
      hmm      Adam Collins      01/01/12 22:20      
         Your Reset Input      Michael Karas      01/02/12 03:56      
            Thanks!!      Adam Collins      01/02/12 07:28      
   Your schematic is wrong      David Prentice      01/02/12 03:35      
   The AT89S52 needs a reset chip!      Kai Klaas      01/02/12 05:44      
      The AVRISP-2 is a USB device      David Prentice      01/02/12 06:02      
   what an AWFUL design      Erik Malund      01/02/12 07:35      
      Isn't mine!      Adam Collins      01/02/12 08:06      
         Compare several schematics      David Prentice      01/02/12 08:16      
            Thanks!!      Adam Collins      01/02/12 08:41      
               Sink or source? Does matter a lot!      Per Westermark      01/02/12 08:50      
                  Not granted      Adam Collins      01/02/12 09:07      
                     Processor can be used      Per Westermark      01/02/12 09:20      
                        Yeah..      Adam Collins      01/02/12 09:33      
                     cure for ignorance      Erik Malund      01/02/12 11:11      
         you forgot the quotes      Erik Malund      01/02/12 08:23      
         well      Erik Malund      01/02/12 08:30      
            Funny      Adam Collins      01/02/12 08:47      
               RC resets are evul      Per Westermark      01/02/12 08:57      
                  So?      Adam Collins      01/02/12 09:02      
                     Not necessarily,,,      Kai Klaas      01/02/12 09:18      
                     I guess you are a student / hobbyist      David Prentice      01/02/12 09:19      
                        Oh..      Adam Collins      01/02/12 09:30      
                        Even or better just then...      Kai Klaas      01/02/12 09:45      
                           Where to apply 100nF?      Adam Collins      01/02/12 10:01      
                              Shortest possible distance      Per Westermark      01/02/12 10:34      
                        especially not for a hobbyist      Erik Malund      01/02/12 11:23      
                  RC RESET worked fine for years ,,, but ...      Richard Erlacher      01/02/12 20:01      
               no, not "will" but "is likely to"      Erik Malund      01/02/12 11:17      
                  an added IMPORTANT comment      Erik Malund      01/02/12 11:26      

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