There is something to be said for the processes of reducing a set of objects or functions down to their lowest common denominator but I think what has really driven me to do this is I am too cheap to go out and buy an Arduino Decemila every time I want to built a new project. But really after doing quite a bit of business with the Logochips I think I understand how important it is to try to design “The little engine that could” do almost anything on a budget. This could be cool, and time will tell what all can be done with it.
So here are the basics to a build your own Arduino clone with a hand full of parts that may cost you no more than about six dollars.
First there is the microcontroller, the brain, the Atmel ATmega168-20PU(costs about $4.00). I should mention here that you need a way to program the bootloader into the Atmel chip. If you have a friend like Keith who will lend you his USBtinyISP and an Arduino Decemila it makes it real easy. Other wise buying one of each might be good if you plan to make a lot of clones.
Next you need to provide the chip with a good 5 volt supply. I suggest the LM7805 and a couple of small capacitors(costs about 50 cents) to regulate just about any voltage down to a nice safe 5 volts for the microcontroller. If you are making a project that already has a 5 volt supply like an old computer power supply you can use that or a set of 4 rechargeable batteries (AA or AAA) works well for those portable projects.
Now the brain needs a clock to keep it on time. That would be this, 16 megahertz crystal resonator (costs about 40 cents). Your probably reading this post on a laptop or desktop computer that is screaming along at 1 or 2 gigahertz well, just slow down, take it easy, 16MHz is just the right speed for the serial communications between the Arduino and your computer.
One more thing. The brain has a tendency to fall asleep. You’ll need a 10,000 ohm resistor (cost 2 cents) to pull the reset pin up to 5 volts and keep the Arduino running. When you download a program from your computer this reset pin gets kicked to tell the Arduino ” HEY I got somthin for ya”.
OK now in the picture here the Arduino clone circuit described above is on the left side and on the right side is another small chip CD40106 which is called an inverter. It and a couple of resistors and a capacitor will condition the signals to and from your computer when your downloading a program to the Arduino. When your done programming you can remove these parts and the Arduino will run by itself. There are three lines of communication that the Arduino needs to successfully download a program, RXD receive data, TXD transmit data, and DTR data terminal ready. The DTR is the one that kicks the reset pin and makes the Arduino gulp down a new program.
So here’s a schematic drawing of the circuit in pdf and also data sheets for the LM7805 and the CD40106 and the XTAL resonator thingy.
Of course none of this addresses any of the many things you can do with the Arduino but that’s another story for later.