I built an Arduino clone with a 328p processor and 8MHz external crystal and burned with the Lilypad w/328 bootloader. I uploaded Blink and it works fine at 5v but is dead at 3.3v. Is there something else besides the bootloader that needs to be done to get it to run at 3.3v?
How did you burn the bootloader? By hand (i.e. from the command-line)? Using the Arduino IDE?
I burned the bootloader from the Arduino IDE, using another Arduino (chose "Arduino as ISP").
Bootloading it should be the only requirement prior to uploading sketches.
More details would be useful to isolate the problem.
Also, how are you powering it (for the 3.3 volt test case)?
I powered it using a known good 3.3v regulated supply, and also from the 3.3v pin on an UNO board. I also successfuly ran it from a LiPoly battery, but it was measuring 4.2v.
I built it using an Evil Mad Science AtmegaXX8 target board, with a brand new 8MHz crystal and two 22pF load caps. Programming is done using a Sparkfun FTDI board at 5v. I have a 0.1uF cap in series between the DTR connection and 328 reset pin. The AVCC and AREF pins are floating. There is a 220 ohm resistor in series with a yellow led from Arduino pin 13 to ground.
It works fine at 5v - programs load and Blink works correctly. With Blink running I measured Voltage on pin 13 and with the unit powered at 5v I get a peak around 5v on pin 13, but powered at 3.3v pin 13 sits steady at around 14 mv.
Hmm, still can't see any problem.
But note that, based on the Atmega328 datasheet, the AVCC pin of the atmega chip MUST be externally connected to the supply voltage as well, even if you're not using the ADC.
Use this as a reference for the connections:
Also, if you're able to, see if you can post a photo of your layout
Finally, when you say "pin 13", you are aware that Arduino-number-13 is not the same as Atmega-chip-number-13, yes? (I believe Arduino-13 = Pin #19 of Atmega328)
Thanks. I will try it with AVCC properly pulled up. Sorry for the pin confusion, I should have been clear about that. Yes, I have the correct "pin 13" selected and connected. I'll post a bit later when I have time to try again with the AVCC correct. I didn't hook it up initially because it worked at 5v. Probably just luck.
O.K., right you are. I connected AVCC to VCC and low and behold it now works at 3.3V! Oops. I won't make that mistake again (really?).
Thanks guys for all of your help!
BTW, giantsfan3, I am originally from Portland. In Boulder, CO now. Hope your weather is O.K.