Custom Arduino 3.3v quick questions. (shouldn't be too hard)

Projects & Topics Product Design
#1

Ok, so I've designed a smaller arduino circuit then my last one. It's pretty much meant to be an LED controller and that's it, so I don't need the 5v for extra circuits or anything. I've only got a few small questions.

1. Do I have to do a special bootloader?

2. Should I attach a 3.3v line to the Aref for buttons/knobs?

3. Being that the led's are tolerable up to 3.5v, do I even need to use resistors on it? Seems kind of pointless if it's within the voltage range. (If the arduino were outputting 3.5v and higher, there'd be something wrong with the arduino if it only had a 3.3v input right?)

That's it. I don't think they are that hard of questions.

#2

1. Do I have to do a special bootloader?

The power supply difference does not require a different bootloader. You only need a bootloader for differences in processor chip or clock speed.

Note that the ATmega328P should not be run at 16 MHz on 3.3V. Many people do buy to be safe you should probably run at 8 MHz.

2. Should I attach a 3.3v line to the Aref for buttons/knobs?

Yes. And connect the various grounds. And put a bypass capacitor between power and ground.

3. Being that the led's are tolerable up to 3.5v, do I even need to use resistors on it? Seems kind of pointless if it's within the voltage range. (If the arduino were outputting 3.5v and higher, there'd be something wrong with the arduino if it only had a 3.3v input right?)

The range given for voltage drop across the LED is not the "acceptable voltage range". The voltage drop is part of the calculation for determining the current limiting resistor and a range is given because it varies from batch to batch. Make sure that the current requirement of the LED is less than the current limit of the Arduino pin.

#3

As far as the 8mhz, I've never gotten it to load right. Well... Should I say, the boot loader uploads (blinking pin 13 led), but I can't ever get it to upload programs after the fact. I tried on four different ATmega328's. They were powered at 5v, but I didn't think that it really mattered.

O-o what about running an atmega8 at 16mhz at 3.3v? Would that cause problems? (I would guess about as many as the 328, but since it's running less memory and ram, may draw slightly less voltage for it)

Also... O-o what do you mean by bypass capacitor? (overall, fairly new to electronics. I understand the need of resistors in most situations, but I thought it was to drop overall voltage, not current, XD Looks like I got those mixed up. sigh)