Sunday, April 22, 2012

Building a Hackduino

I installed the bootloader on 25 atmega268 chips that I just bought following these directions: http://arduino.cc/en/Tutorial/ArduinoISP .  But now what do I do? 

That is when I saw the hackduino project here: http://www.instructables.com/id/Perfboard-Hackduino-Arduino-compatible-circuit/ This looked very interesting and I knew that I could complete this project with minimal effort. I also thought that I could route the wiring so that it took up minimal space. I wired up the power supply, timing and reset functions to my own hackduino version. I am trying to run the wires in a sane way.   One of the nice things about the hackaduino in this form factor is that there is a lot of space for your own circuits on the board.  You can be a lot more compact than the standard Arduino form factor.

Here is the front of the board, it looks very neat and clean.

Here is the back of the board, I am a little rusty with soldering still.

I did not hook up the aref pin, because the atmegaX68 chips default to Vcc. There is info here about aref: http://arduino.cc/en/Reference/AnalogReference?from=Reference.AREF I had a solder bridge at first which really heated up the power regulator chip fast. I fixed that and tested that I have 5v across the positive and negative power strips. So far I am very happy with the project. I am taking pictures as I go and will try to make my next version look neater so the pictures look better. My plan it is to get the first one running, then build a half dozen of this version, with maybe some power options different for different configurations.

The power comes in on the red wire, at least 7 volts. The ground is shared between the input and the middle power rail. The top rail is 5 volts.

A 1K ohm resistor is hooked to pin one and 5V. The switch shorts this to ground to reset the processor.

There are a couple of layers of power here. Each side of the chip needs ground and power. A ground and power goes right from the rails and to the chips. To get from one side to the other one ground and one power has to cross the opposing rail, so they are insulated.

The crystal hooks between pins 5 and 6 from the bottom left looking down from the top. each pin is then taken to ground with a 22uH capacitor.

 In the morning I am going to try to power up and run my first board after I double check that I wired in the power and ground connections to the right place. I am looking at adding the ftdi interface to allow communications with the development environment. I found some info on how to wire it up from this site: http://thetransistor.com/projects/arduino/ Which gave some info about adding a jumper to power from either the power regulator chip, or from usb 5v power. It would be interesting to power the board from just a usb connection. This would be very interesting if I installed one of these chips into my netbook computer.

Note a couple of years later:  I have used these board in a few projects now and they work very well.   The only issue is trying to program them.  It sometimes takes a few tries before the chip accepts a new download.  There is something about the serial interface that I am missing.

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