stand alone atmega328 help

Hello everyone,

Application: I have an Orangerx transmitter in which I am "customizing". I am using a stand alone atmega328 to read the potentiometer values from the tx via the adc's. I will then take those values and manipulate them based on the goal of the output. I will then send a "potentiemeter" value using a 12bit digital to analog converter that communicates to the atmega328 via i2c.

Problem: the circuit I have setup has the atmega running on 3.3v at 8mhz with its internal oscillator. I burned its bootloader and program it via aruino uno as isp. I ran a simple blink led on pin 13 sketch and it works on a breadboard at 5v but not 3.3v. But my circuit runs on 3.3v and not 5v.

any suggestions are welcome cheers!

Post your schematic.

Problem: the circuit I have setup has the atmega running on 3.3v at 8mhz with its internal oscillator. I burned its bootloader and program it via aruino uno as isp. I ran a simple blink led on pin 13 sketch and it works on a breadboard at 5v but not 3.3v. But my circuit runs on 3.3v and not 5v.

Did you remember to burn the fuses for the 328P @8MHz?

I run these chips @8MHz all the time, they work.

here is my schematic, its not the best but oh well. disregard the section where i have a 16mhz crystal with two 22pf caps(I took that out because I previously found out you cant run it at 16 Mhz @3.3v).

dbutler0526: here is my schematic, its not the best but oh well. disregard the section where i have a 16mhz crystal with two 22pf caps(I took that out because I previously found out you cant run it at 16 Mhz @3.3v).

It is probably possible to run at 16MHz at 3.3V. Maybe a 16MHz 3.3V external oscillator (not a crystal) would work?

No it won’t because in the datasheet for the atmega328 you can only run speeds up to 10Mhz while at 3.3v
But that is besides the point as it doesnt help in my situation.

dbutler0526: No it won't because in the datasheet for the atmega328 you can only run speeds up to 10Mhz while at 3.3v But that is besides the point as it doesnt help in my situation.

I would say there is a good chance that it will even though it would be out of spec. Every AVR sample I have tested runs lower than its rated voltage at a given speed.

LED needs current limit resistor. AVCC needs 3.3V input also. VCC & AVCC pins need 0.1uF cap to Gnd. 10K resistor from Reset to 3.3V - looks like you have it pulled low instead.

What fuse settings are you using? 8 MHz/3.3V is a good combination - that's what you'll find on 3.3V ProMinis. You really need the above - especially AVCC connected to VCC, and the current limit resistor.

I have .1 ceramic caps in, I just didnt put them in the schematic. I have reset pulled high in the circuit, but i have it low on the schematic. Oops I will put a resistor in tomorow.

Connect AVCC to 3.3V too.

Thanks Crossroads! I hooked up avcc to 3.3v and it works. and i threw in a current limitng resistor too. Back in business. :grin: