AVR-Chat

ethan@bufbotics.org wrote:

> Ok, cool.  Thank you all for your enthusiastic responses.
>
> To summarize your ideas (and toss in a few new questions):
>
> 1) On the RESET pin, I should use a diode (and pull-up resistor) as
> documented in Atmel AppNote AVR042.  They also have a capacitor in the
> note, do you guys recommend that as well?

A capacitor can be useful if you have a reset switch, to avoid resetting 
caused by noise on the input.


>
> 2) Dont waste B6 on a heartbeat, since that pin has too many other
> alternative uses.  Perhaps A7? Then I'd only be losing an ADC, correct?
>
> 3) There's better voltage regulators than the 7805.  Well, for this
> particular project, I'm going to stick to the age old "a voltage regulator
> in the hand is better than two in the bush" and use the 7805 sitting in my
> basement.  Any recommendations for the next time I'm in the mood to buy
> some regulators that're in the same neighborhood as 7805?

ST makes an LDO regulator in TO92 which I often use. It's similar to the 
78L05, but much better.

>
> 4) No pull-ups needed on MOSI, MISO & SCK. I understand that they aren't
> needed if I'm not using those 3 pins for general I/O use, but according to
> the same AppNote mentioned above (AVR042), in figure 5 on page 6, they
> recommend 4.7k resistors in between the pin and any I/O load.  SOOOOO,
> even though I didnt connect anything in my schematic, let's pretend I was
> going to use B0-2 for something else.


You've got them connected wrong, they should be in series with the ISP 
connector pins, not used as pullups.


> Do I need a resistor in the
> following situations:
>     * using a pin as output
>     * using a pin as input
>     * using a pin as PWM output
>     * anything else?

You might need a pullup resistor sometimes on inputs, the built-in one 
is rather 'weak'. You also need one if you are using I2C devices.

Leon


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