Atmega 2560 at 8Mhz and 3.3V

Other Hardware 3rd Party Boards
1

Hello,
I am in making a device for my rugby team, where i am using Atmega2560 MCU to log data in to a SD card, the data like 10Hz GPS data, Heart rate, Acceleration and USB to SD converter, All of the devices like GPS,Accelerometer,SD card, USB to SD converter and Heart rate monitoring chip uses 3.3V. To make signalling properly i have to use Logic Level Shifters for every line connecting from other devices to Atmega2560..

Is there any way i can use Atmega2560 at 3.3V OR any other chip do this job.?

P.S my code is made in Arduino IDE, If suggesting other chip please also mention if it works with my code or not.

Sketch uses 27,008 bytes (10%) of program storage space. Maximum is 253,952 bytes.
Global variables use 1,884 bytes (22%) of dynamic memory, leaving 6,308 bytes for local variables. Maximum is 8,192 bytes.

Thank you

2

Yes, the ATmega2560 is rated for 8 MHz at 3.3 V. There is a 3rd party hardware package that has the correct fuses, bootloader, and even pin mapping for all the pins if you want:
https://github.com/MCUdude/MegaCore/tree/avr-100-pin
A production release of this version of the package hasn't been made yet so you will need to follow the manual installation instructions. Please report if you discover any bugs.

3

Hello pert,

I have installed the boards into my Arduino IDE, but i couldn't find Atmega2560 in the list

Please see attachment

Screen Shot 2017-05-17 at 4.44.42 PM.png

4

is it only for ATmega64, ATmega128, ATmega1281 and ATmega2561.?

5

https://github.com/MCUdude/MegaCore/tree/avr-100-pin
A production release of this version of the package hasn't been made yet so you will need to follow the manual installation instructions. Please report if you discover any bugs.

6

Thank you hansibull,

I can now try it with 8Mhz and 3.3V on Atmega2560, I will have a test with it, BTW! i am using the libraries below... does it supports.?

#include <Arduino.h>
#include <NMEAGPS.h>
#include <SPI.h>
#include <SdFat.h>
#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_ADXL345_U.h>
7

As long as the libraries supports the ATmega2560 (which they mostly do), they will work @ 8 MHz :slight_smile:

ATmega640/1280/2560 will be available through the boards manager as soon as all testing is finished.

8

Thank you very much hansibull,

and what is internal clock,under the Tools section - is that mean i don't have to use External 8Mhz crystal with 22pF load caps.?

Please see image..

Screen Shot 2017-05-17 at 6.42.56 PM.png

9

The Atmega2560 has an internal 8 MHz crystal that you can use. This means you actually don't need an external one. Simply select "8 MHz internal" and hit "Burn bootloader" to load it on the microcontroller. What kind of board do you have?

10

Hello Hansibull,

I have my own fabricated PCB which consists of Atmega2560 and a 16Mhz crystal with 22pF capacitors and other devices and sensors..

11

No problem. Then the crystal (and caps) are just not used :slight_smile:

12

Read the data sheet - the Atmega2560 needs 4.5V to 5.5V for all speeds:
ATmega2560/ATmega2561:
• 0 - 16MHz @ 4.5V - 5.5V

If you want to run at 3.3V, you need Atmega2560V:
ATmega2560V/ATmega2561V:
• 0 - 2MHz @ 1.8V - 5.5V, 0 - 8MHz @ 2.7V - 5.5V

13

That means i cannot use 3.3V supply with my Atmega2560 even if it's with Megacore boards.?

14

Not if you want it to run fully in spec.
Most things may work, some things may be flaky, some things may not work at all.
If you want it guaranteed to work, change to a '2560V processor.

15

What's ironic is that it still has a 2.7v BOD fuse setting!

However, I can confirm that its little brother (the ATmega2561) works perfectly at 3.3v running on the 8 MHz internal oscillator (even though the datasheet specifies 4.5v) :slight_smile:

16

"It works" and "is within spec" are two completely different things :wink: Because if you're out of spec and it works there is just no guarantee it keeps working.

17

Hello,
Thank you all for your rapid replies,
I am using lvc125a quadruple bus buffer gate in between my Atmega 2560 and SD card.

So, if I use Atmega 2560v, then I don't need lvc125A?

One more question : can I burn bootloaders of a normal Atmega 2560 to Atmega2560V ?

Thank you

18

If you use the ATmega2560V running at 3.3v, you don't need a level shifter between the DS card and the microcontroller. You can stilll burn the ATmega2560 bootloader on the ATmega2560V.