Hi,
I have been looking for days for a solution on how to run an Atmega328p-pu at 3.3v.
The problem arises with wanting to run a small battery project with an atmega328p at 3.3v, so I inquired and saw some video showing that you can use this 3.3v chip with 16mhz. I tried to make it work at 3.3v with 16mhz but I can't (for example with a blink, the led does not turn on), plus I discovered that with this configuration you are at the limits of the safe area according to the datasheet, so I found on the internet a solution and says to use an 8mhz crystal. I tried to make it work at 3.3v with 8mhz, but even here the led does not turn on (as well as the delay is double, but that I understand why). Can anyone get me a little guide on how I should go about making an Atmeg328p-pu work with 3.3v? the crystal can be either 16mhz or 8mhz, preferably 8mhz for battery saving.
Shall we start by going over the schematic of your circuit and a good photograph of how you've built it? Then when we've established that the hardware is OK, we can focus on the software side.
This is the circuit equal to an internet video where i tested the two crystals and different voltages (the led is connected to digital pin 9, 220 ohm):
Ok, did you notice in the pinout of the 328p-pu that there's two pairs of GND and Vcc pins? You've only connected one of each at least on the breadboard version (can't tell if it's also the case on the perfboard ones). Try connecting ALL GND and Vcc pins, otherwise the chip won't (shouldn't) work.
No.
Pins 8 + 22 are GND. Both need to be connected.
Pins 7 + 20 are Vcc. Both need to be connected.
Pin 21 is Aref. You can leave that one unconnected.
Btw, those wires sticking into your female headers are a marginal solution. Soldered connections are far more reliable.
Also, did you verify the correct value of the capacitors around the crystal? They should be 22pF. In practice 18pF to 33pF will likely work OK. It's a common error for people to connect 22nF, which won't work.
Is the Pro Mini better for a battery project than the atmega328p? i know that somebody remove the led on board of the pro mini. On my project i will wake up atmega328p every 1 minute for just 5 seconds.
Exact same processor, just in the SMD form. Two extra analog-only input pins available due to the different package.
Not necessarily better or worse, but you buy it fully assembled with all support components (and a couple not necessary) in a form that is proven to work and it tends to cost no more (and generally less) than purchasing the separate components.
Yes, for battery operation you remove the resistor that connects the pilot LED and the regulator which was always pretty useless.
