Introduction: Bootload an ATmega328
This instructable adds to any of the Arduino on a Breadboard instructables. I wrote my own breadboard-Arduino tutorial, and then I found that I was struggling to program some of the boards I made. A lot of research and dead-ends got me understanding that:
1. You either need a microcontroller with a pre-loaded Bootloader, or must load your own
2. Not all ATmega328’s are equal
(A bootloader, very simply, is a programme that sits on the chip and manages the upload of your sketches onto the chip)
There are plenty of bootloading resources, but I couldn’t find a single one that pulled everything together in a way that made sense to me.
If this instructable helped you, please visit Crash Bang Prototyping, follow us on twitter, and join in with our prototyping resources and tools.
Step 1: Parts
Step 2: The Approach
We’re going to use the Arduino UNO to bootload the ATmega328 that is sitting on the Arduino-on-a-Breadboard. This is fairly straightforward if you have an ATmega328P-PU, but needs an extra step for an ATmega328-PU. I’ll tackle the differences later in the Instructable.
Step 3: Program Your Arduino UNO As an ISP
We need to program the Arduino UNO to act as a an ISP (In-System Programmer), so that it can burn the bootloader onto the Breadboard chip.
- Open the Arduino IDE
- Open the ArduinoISP sketch (under File, Examples)
- If you’re using version 1.0 of the IDE:
search for void heartbeatand change the line that reads:
Connect your UNO to the PC, making sure it’s not connected to the Arduino on a Breadboard.
Ensure your UNO is selected under the Boards menu option, and upload the sketch.
Step 4: Connect Your ATmega328
Now connect your ATmega to your UNO as follows:
- UNO 5v ---> ATmega pin 7 (VCC)
- UNO GND ---> ATmega pin 8 (GND)
- UNO pin 10 ---> ATmega pin 1 (RESET)
- UNO pin 11 ---> ATmega pin 17 (MOSI)
- UNO pin 12 ---> ATmega pin 18 (MISO)
- UNO pin 13 ---> ATmega pin 19 (SCK)
Make sure that you don’t have anything else connected to the ATmega pins used above.
Step 5: Which ATmega328 Are You Using?
I learnt the hard way that there is more than one type of ATmega328. The two variants that are of interest to us are the ATmega328-PU and the ATmega328P-PU.
The -PU suffix means that the chips are in a PDIP package, the format we need for our breadboard.
The 328P is a picoPower processor, designed for low power consumption, and is used on the Arduino boards. Given low power consumption this is first choice.
The 328 does not have picoPower technology, and is not used on the Arduino boards – and is not explicitly supported by the Arduino IDE.
What this means is that we can easily bootload the ATmega328P, but not the ATmega328. Unfortunately the websites that sell these chips don't always differentiate between them and forums are filled with people struggling to use the ATmega328-PU.
Luckily there is a workaround - take a look at my Crash Bang website.
Step 6: ATmega328-PU Workaround
Each microprocessor has a signature – a unique code that identifies its model. When you bootload a chip (or even upload a sketch) the Arduino IDE checks that the chip selected matches the type it’s connected to. Even though the ATmega328-PU in essence functions in the same way as the ATmega328P-PU, it has a different signature, and one that isn’t recognised by the Arduino IDE.
(Behind the Scenes: The Arduino IDE actually uses AVRDUDE to programme the chips, so you’ll see error messages from avrdude)
If you try to bootload an ATmega328-PU, you’ll get a message something along the lines of:
avrdude: Device signature = 0x1e9514
avrdude: Expected signature for ATMEGA328P is 1E 95 0F
Double check chip, or use -F to override this check.
You could also get a more colourful version:
avrdude: Yikes! Invalid device signature.
The way to work around this is to “trick” the IDE into believing your 328-PU is in fact a 328P-PU. Disclaimer: I have tested this myself and it works – no guarantees however that you won’t have unforeseen consequences.
In your Arduino folder, find the subfolder: ..\hardware\tools\avr\etc
- Make a backup copy of the file: avrdude.conf
- Open the file avrdude.conf in a text editor
- Search for: “0x1e 0x95 0x0F” (this is the ATmega328P signature)
- Replace it with: “0x1e 0x95 0x14” (this is the ATmega328 signature)
- Save the file
- Restart the Arduino IDE
- Continue with the rest of the steps in the instructable, and once bootloading is complete restore the backup copy you made.
Step 7: Bootload the ATmega328
In the Arduino IDE, from the Tools menu:
- under the Board option choose Arduino UNO
- under the Serial Port option ensure the correct port is selected
- under the Programmer option choose Arduino as ISP
To burn the Bootloader, choose Burn Bootloader from the Tools menu
You should see a message “Burning bootloader to I/O Board (this may take a minute)"
Once the bootloader has been burned, you’ll see a message confirming the success.
Congratulations: You're now ready to load sketches onto your Arduino on a breadboard!
ATmega328P-PU: You can leave your setup as it is, and use the Arduino UNO to upload sketches to your newly bootloaded ATmega (File, Upload using Programmer).
ATmega328-PU: the IDE will notice that the signature isn’t valid – so you’ll have to either alter the avrdude.conf file again or use an FTDI board to upload. I prefer using an FTDI board anyway as it doesn’t take my UNO out of circulation and is quick to connect.
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