Hi all. I'm working on a project and have opted to use an Arduino for development. The chip will be on a PCB in the end but I only have +-2.5 V rails to my disposal. Will the ATMega that I took off my Arduino Uno be able to run off of 2.5V VCC (using the external 16MHz clock)? If not, would I be able to connect the GND of my Arudino to the -2.5 rail in order to achieve the required 5V drop? I haven't been able to find any material on the atmega chips to give be a definitive answer. Obviously, my other option is to burn a bootloader onto my chip that uses the internal 8MHz clock but I am incredibly pressed for time and found out about 5 minutes ago that I cannot use my Uno as an ISP which really limits my options.
As long as the +2.5 and -2.5 rails have a common Ground and you DO NOT CONNECT THAT GROUND TO ANYTHING CONNECTED TO THE ATmega you can use the -2.5 rail as Ground and the +2.5 rail as +5.
Ok, that's what I was hoping. Now, just to be completely clear, I am using 2.5V as a reference for my analog reads. If I am using the -2.5V rail as ground, I will have an analog reference range of 5V (from +2.5 to -2.5), correct?
As far as the Arduino knows it's power is 0 and +5. If you feed your 'Ground' wire to an analog input it should get a value around 512 (1/2 full scale or +2.5V)
You can? I was trying and I kept getting avrdude errors. Had the ISP sketch and the boards.txt files all updated and it still didn't work so I just assumed that the page was still relevant. Do I just follow the same steps outlined in the tutorial or is there something special that needs to be done?
fronzbot:
You can? I was trying and I kept getting avrdude errors. Had the ISP sketch and the boards.txt files all updated and it still didn't work so I just assumed that the page was still relevant. Do I just follow the same steps outlined in the tutorial or is there something special that needs to be done?
Be sure to disable the auto-reset on the UNO. After uploading ArduinoISP connect a 1 to 10 microfarad capacitor from Reset (+) to Ground (-) or, alternatively, connect a 100 to 120 ohm reeitor from Reset to +5V.
johnwasser:
Be sure to disable the auto-reset on the UNO. After uploading ArduinoISP connect a 1 to 10 microfarad capacitor from Reset (+) to Ground (-) or, alternatively, connect a 100 to 120 ohm reeitor from Reset to +5V.
Hmm, I've tried the resistor to high but not the cap to low. I'll give that one a go when I get a chance, thanks!
John_S:
FWIW, I don't need a resistor or capacitor. I don't know why if everyone else does?
Upload the ISP sketch to your UNO
Close the IDE (I'm using 0023)
In preferences change upload.using=bootloader to upload.using=arduinoisp
Reopen IDE, select the board version you want to upload to (nano, UNO, attiny, ect. I use UNO when it's a standalone 328)
Connect all appropriate wires from your UNO to the board you want to upload to.
Upload your sketch with the upload button.
Perhaps there's a bit of a mis-communication here. The chip I will be using does not have a bootloader. The steps you listed seem fine for a chip that already has a bootloader but mine will not which is why I wanted to use the Arduino as an ISP. Aside from the preference file changes (I changed it right in the IDE) I already performed those exact steps to no avail, unfortunately.
I don't use a bootloader either. That's why you need to change the preferences.txt file to reflect that. I don't know how you change the preferences in the IDE. You have to exit it, change the preferences, save the preferences file, then reopen the IDE.
