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push buttons + led interface to avr pins

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sherazi

sherazi

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i am interfacing push buttons and leds to avr in such a way that when the button is pressed the led also glows.. now the point is that i want it to glow by itself and not by mcu ... check the circuit ...attached..
84_1286179499.png


when i used the same circuit during testing using 5mm LEDs the system worked.. a valid zero was avaible on pin of mcu, but hwen i made some prototype boards using SMD LEDs the PIN doesnt get valid zero, i checked the Voltage across the LED when it was on and that was 2.1 V ... what i can i do to make it valid one...
 

hi
you should solve this problem with connect avr pin in below led & turn on pull up resistor in avr
if turn on led with low light must be reduce R1
 
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    sherazi

    sherazi

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thanks alot... i know LED isnt bright with 4.7K but its the level i want...
but 1 querry ? why to turn on internal reisistor if external pull ups are uesd?
 

Hi,
When the LED is ON, it will have typically 2.0V across its terminals. That's why you are getting invalid "Zero".
As mohammad hassanzade said, you need to connect your AVR to the LED's cathode pin so you can get a valid "Zero" when the button is pressed.

Hope this helps.
 

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