AVR-Chat

Normally, you would do this just leaving the pin as an
output. Put a resistor between the transistor base and the
port pin to reduce the base current. A 1K ought to work in
your situation. 

But, for your further questions, there is no limit to the
number of time you can change a port pin from input to
output or back again. The only place in the whole micro
that has limited number of operations is write to
non-volatile memory (either flash or eeprom, though the
numbers are different).

Jim

On Tue, 31 Jan 2006 10:57:29 -0000
 "Ted Smith" <tedsmithau@yahoo.com.au> wrote:
> I want to use an ATMEGA16 to drive three sets of
> transistors to each
> switch 6 high brigtness LEDs in parallel from 1 output
> (240ma per set). 
> There is not enough current in the AVR to connect the
> LEDs directly
> without additional parts.
> I propose to connect the AVR output pins directly to the
> base of a NPN
> transistor.
> Initially for the lights to be off, I would program the
> port pin as an
> output at 0 volts so the NPN transistor would not
> conduct. 
> To make the lights go on, I would change the port to an
> input (with
> pullup resistor enabled). This internal 10k pull up
> resistor would
> easily sink the transistor on and light up the leds
> connected between
> the collector and vcc+ with their 165 ohm dropping
> resistors.
> This would need no extra base resistors.
> 
> 1. Can anyone see any problem with this? 
> 
> 2. Is there any limit to the number of times you can
> change from an
> input to an output and back again?
> 
> 3. What would be the best way to do this with Bascom? 
> 
> There is a veiled note about having to make something
> tri-state when
> changing from an output to an input in the specs but I
> cant understand it.
> 
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 

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