Hi all,
I have an issue with the Arduino Mega that i recently purchased that i am having trouble understanding. I have a custom built circuit that I am controlling with the digital I/O lines using an Arduino Uno. I am simply using the Arduino to enable or disable clock oscilliators on the circuit and control some multiplexers that select the clock frequencies. Programming and functionality using the Arduino Uno, everything works great, but I needed more control lines and ordered an Arduino Mega. I swapped the Uno for the Mega and the Mega does not work. The program works fine on the Mega and the I/O lines produce 5V when I turn them on, but when i connect the I/O lines to the circuit, the voltage output from the I/O line drops from 5V to 500 mV. This only happens with the Mega, not the Uno. The current draw is minimal from the circuit (maximum 1 mA per I/O line) which should be easily within the capabilities of the Mega. What is the difference between the two boards that could be causing this? Are the built-in step-up resistors for the I/O pins enabled by default on the Mega perhaps? I could use two Uno's in parrellel but I would rather figure out why the Mega is not working. Please help.
"Either the mega is damaged or you are not connecting the hardware the same way."
The hardware is connected the same. Maybe the Mega is damaged. Instead of using the digital pins on the Mega (22-53), I used the PWM pins (pin 2 specifically) on the Mega as an output pin and the circuit works fine (5V measured on pin2 when my circuit is connected and I enable pin 2), just like on the Arduino Uno. All I am doing is moving my connecting wire from pin 2 to pin 22 and changing my code to enable on pin 22. The output on pin 22 drops from 5V to 500 mV when i connect my circuit. All of the PWM pins seem to output normal voltages but all the digital pins seem to be incalpable of maintaing 5V when connected. Unless I am missing something obvious, maybe the digital output portion of the Mega is damaged ( I hate to order another one just to find out). Should there be a difference in digital output between the PWM pins (2-13) and the digital pins (22-53)? Thanks.
Sass
It should be noted that when I use the Arduino Uno, I am using pin 2 as well (not a PWM pin) and it works fine
ssirsi:
maybe the digital output portion of the Mega is damaged
That's really not how the chip works. There isn't a "digital output portion". The PWM pins use the same hardware whether you are using it as a PWM or a digital output. (PWM is after all just a digital I/O that toggles.)