Wednesday, January 22, 2014

Reusing some old microcontrollers Arduino style

The other day I was cleaning up my electronics boxes and I happened on 2 older Atmega32 40 pin controllers I got a long time ago, when first starting my foray into MCUs. I remember those times when I was trying to figure out how to program a controller, when no Arduino was around and everything was done directly in C at pin level, same as I still do now for MSP430; with lots of friends and forum help, I was able to blink an LED even drive an H-Bridge. Cool and also frustrating times! An idea struck me: if people are able to create Arduino like IDEs for all kinds of controllers (see Energia for MSP430 and LaunchPad) maybe it would be possible to program these MCUs the same way: after all, they are Atmel controllers so it shouldn't be that difficult. It all has to start with burning the bootloaded, since this is what makes the Arduino what it is today. It turns out some people figured out how to do this, not very easy but not very complicated either. The post I found most helfpul is here. Thousand thanks to hexskrew for figuring this out!

First thing to do was install Arduino-0022 (I already have 1.0.5 installed but the arduino-extras was written for pre-1.0 versions, didn’t want to go through the pain of updating the code and mess it up for sure) and replace the arduino folder with the content of Also, in Preferences, I unckecked “Check for updates on startup” because I want to keep this Arduino version as it is - newer versions will apply to my other Arduino-1.0.5 install.

Most important step is wiring the Atmega32 to the Arduino: I have an ISP programmer somewhere but using an Arduino instead seemed to be easier for someone like me. The schematic is shown here and is great!I wired everything as in the image but since I didn't have a 120 ohm resistor, I decided to use a close one instead, 150 ohm. It says clearly in the image that the resistor MUST be 120 ohm but my limited experience said: if 120 ohm can do the job, why not a 150 ohm! Big mistake that cost me quite some time! (Now I know I should listen to my betters and not assume anything, especially since I am just a noob in electronics.) Running the first command in the document:

avrdude -p m32 -c arduino -P /dev/ttyUSB0 -b 19200

I got instead of the expected response:

avrdude: Device signature = 0x1e9502


avrdude: Device signature = 0x1e9406
avrdude: Expected signature for ATMEGA644P is 1E 96 0A
Double check chip, or use -F to override this check.

I googled around and found the same exact message in this post which in turn links to this doc in Arduino playground where it is explained with details that the resistor must indeed be 120 ohm! I dug into my box of resistors in the end found a few that connected together yielded the desired 120 ohm. I reran the previous command again and this time I got the expected reply. Awesome!

Note: there is a difference between the original schematic I followed and the last article I mentioned: in the original one, the 120 ohm resistor is between RESET and GND; in this article is between RESET and 5V. I assume they both worked but I decided to go with RESET to 5V.

The commands are listed and detailed in the post I mentioned above, in a nutshell what I did to burn the bootloader was:
  1. Check everything is ok
  2. Set the chip to be unlocked, and use the internal 8mhz oscillator
  3. Unlock to bootloader
  4. Flash the arduino bootloader
  5. Lock the bootloader.
After this was done, I got the example sketch and tried to compile. I had several errors some that may have been Linux Mint specific (maybe because I already have newer avr libraries installed for Arduino-1.0.5) but this and this posts helped me fix them so in the end the sketch compiled successfully. I uploaded it to the Atmega32 the way it is described in the post - I still need to figure out how to upload it directly without copying it manually from /tmp to /bin. It was getting late when I finished this so I didn't get to test it - I assume I will have to disconnect the SPI communication with the Arduino first. I'll try soon and post back here.

Again, big thanks to hexskrew for figuring this out!

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