uDuino: Very Low Cost Arduino Compatible Development Board

Step 4 External oscillator-based board build

Collect the parts you'll need:

- Breadboard (you can of course build this straight on a predrilled PC board as well)
- ATmega168 chip with bootloader pre-loaded
- .1uf capacitor (ceramic, polyester, etc. doesn't matter so much; value .047uf-.47uf should be fine)
- 10K resistor (values ~3.3k-20k should work fine)
- 16mHz 3-pin ceramic oscillator (preferably with longish, e.g. 1/2 inch, leads)
- Short lengths of wire

Put the ATmega168 in the breadboard, straddling the center.

For each of the following connections, use the hole at each ATmega168 pin that is the closest to the chip that is open; this will leave the last hole in each of the rows 1-8 open for the programming cable to plug into.

Connect pin 7 and 20 with a length of wire (VCC to AVCC)
Connect pin 8 and 22 with a length of wire (GND to AGND)
Connect the 10K resistor from pin 1 to pin 7 (RES to VCC)
Connect the .1uf capacitor from pin 7 to pin 8

Connect the outer pins of the oscillator to pins 9 (XTAL1) and 10 (XTAL2) of the ATmega168. It doesn't matter which of the pins connects to which ATmega pin.
Connect the center pin of the oscillator to pin 8 (GND)

If you have power bus lines on your breadboard, I suggest connecting the + rail (red) to pin 20 and the - rail (blue) to pin 22. This is somewhat bad form (connecting to the analog side for power connections for other stuff), but if your breadboard is the same size as mine you've already filled all of the holes available for pin 7.


If you're planning to use USB power, you can now just plug in the programming cable and upload sketches to the board (make sure to connect the power selection pins on the cable adapter with a jumper to power the chip from USB).

Otherwise you'll need to use a battery/voltage regulator/etc. to supply power.

Comments

[bigjeff5]

If you're concerned about your oscillator tolerances, you should be using crystal instead of ceramic. 0.5% tolerance is much better than the internal oscillator, but crystal has 0.001% tolerance, and the cost is about the same (70c'ish). Plus, the crystal kind are only two pins, which are way, way easier to install on solderless breadboard. You can run 20mhz as well if you want, the ATmega can handle it (that's it's peak rated speed). Your timing functions will need to be adjusted to compensate if you do run it that fast, though.

[tymm]

Main reason I picked a 3-pin ceramic resonator is because it won't need extra capacitors (in a breadboard there will probably be enough capacitance for it to work anyhow -- though if moved to prototyping board the circuit may well stop working). Ceramic resonators give less accuracy, it's true... though for solid serial communications they're absolutely fine across standard temperature ranges, which the internal oscillator isn't guaranteed to be. And they actually are a bit cheaper, though it's true the difference isn't a big deal for 1-offs. But totally agree if higher precision is needed that a crystal is a better choice.

[bigjeff5]

That's a good point. Excellent Instructible tymm.

[Maniacy]

Oh c'mon! This is like THE tutorial I was looking for, plug'n'program... and then you give me this photo? Seems as if would have to figure it out by myself after all... Good tutorial anyway, thx!

[gib0r]

Read a datasheet.