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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