push buttons + led interface to avr pins

[sherazi]

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..

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...

 

[darkman1969]

A 2.1v drop across a led sounds like your using a Green or Blue LED. Try using a Red LED and see what happens.

 

[sherazi]

got the point ... i should connect to avr b/e sw1 and led

 

[(*steve*)]

A better option is to place the connection to the AVR at a point between the switch and the LED. Then place a high value resistor (47K should be fine) across the LED. This will ensure the input sees a full rail to rail swing, regardless of the colour of LED you use.

 

[sherazi]

ACROSS THE LED?

CAN YOU PLZ ADD SCH TO YOUR REPLY

 

[darkman1969]

'Across the led' means, place the resistor so it is connected in 'parallel' with the led.