AVR-Chat

Ted Smith wrote:
> After reading the various replys to my original comment I apologise
> for upsetting anyone and it was not my intention to start a diatribe
> on the subject.
> It's just that we in Australia are sensitive to being put down (Eg.
> references to being "down under") and naturally have the desire to set
> things straight.
> I shall stick to purely technical matters in future.
> Ted

I couldn't care less if we were called "down under", because we are
when considering the traditional top end as the north pole. I know
no one else that would object to it either.

OTOH, our "leaders" cutting freedoms by slavishly following Bush beating
about the bushes to flush out "commies" and "terrorists" is what most of
us down-under object to.

Ted Smith 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?

You'll need to use darlingtons for more gain, or waste power with smaller
pullup resistors.

 > 2. Is there any limit to the number of times you can change from an
 > input to an output and back again?

No.

 > 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.

You program a "one" on the Port pin to drive the pullup, but leave the Pin
programmed as an input.