Building an Arduino on a breadboard or circuit board

[chrisjpf33]

I have seen people commenting on various websites about how you can build an Arduino on a breadboard. Most of the circuitry is straightforward, but I have seen conflicting comments regarding the crystal oscillator. Adafruit uses a 3 pin ceramic resonator on the new MENTA board (what are the specs on this part anyway?). Other people use a crystal with two 22pF capacitors. Some people say that the crystal selection is critical (I didn’t know there were different types of crystals, just different frequencies). Some people say that they prefer 18pF caps. It all seem like it is more complicated that it has to be.

What is the best answer to selecting this(these) parts? I realize that there is a cost consideration, and well as the issue of physical space on the board, but for the sake of this post I am more focused on reliable function. What will work, what won’t, and why?

Thanks in advance for your advice.

Chris

[adafruit]

You can get specs for all the MENTA parts here, we selected these, use these in the MENTA and suggest these for reliable function.

http://ladyada.net/make/menta/parts.html

[floresta]

What is the best answer to selecting this(these) parts?

What is the best car to buy?
Should I buy a GM product or a Toyota product?
Should I buy a Chevrolet or a Cadillac?
Should I buy a Toyota pickup truck or a Toyota sedan?
Should I buy a red sedan or a blue sedan?
Should I buy the sedan with or without a radio and a heater - oops I just gave away my age.

Don

[adafruit_support_mike]

Different kinds of crystals are cut in different shapes, so they resonate in different ways and have specific temperature, stability, or aging properties. The 'AT' cut is the most common, and the best advice for a beginner is "use what it says on the circuit diagram unless you know specifically why you need something else."

A crystal sitting on two capacitors is called a 'Pierce oscillator', and is the most common kind of crystal oscillator. The size of the capacitors has some influence on the frequency (stability, temperature response, etc), and some people will play with the values to get specific results. Again, the best advice for someone new is, "use the values from the circuit diagram until you know how to build something else."

Ceramic resonators are all-in-one devices. You plug 'em in, power 'em up, and watch 'em hum.

The big difference between crystal oscillators and ceramic resonators is frequency stability. Basically, crystals are really good.. a decent crystal oscillator's frequency will only drift from its average value by a few parts per million. A ceramic resonator will drift by about .5%. An RC oscillator (like the chip's built-in clock) usually drifts by about 5%.

The big question is "how much accuracy do you need?" Crystals are good for communications gear and timekeeping, because the whole point of the game there is to be stable, predictable, and reliable. For a microcontroller that isn't doing hard-real-time work, a ceramic resonator (or the chip's internal oscillator) should be just fine.

If you're working on a breadboard, you don't need much accuracy.. or perhaps more correctly, you won't get much accuracy.

Breadboards are notorious for having lots of parasitic capacitance, and for causing all sorts of problems at high speeds. Analog design guru Bob Pease used to call them "white blocks of pain". Putting a crystal oscillator in a breadboard would be like trying to use an electron microscope in the back of a pickup driving down a gravel road.

Honestly, you'd be just as well off to forget about an external oscillator entirely and use the one built into the chip, at least as long as you're working in the breadboard. If you find yourself needing more frequency stability than the chip can provide for itself, you'll have to switch to another construction technique to get it.

[pylon]

Please keep in mind that you have to change the bootloader if you wanna use the internal oscillator (good tutorial: http://www.instructables.com/id/uDuino-Very-Low-Cost-Arduino-Compatible-Developme/step5/OR-internal-oscillator-board-build/) and choose "Lilypad Arduino" as your board type in the Arduino IDE.

[CharlieD]

Here is a picture of a "bare-bones" breadboard I use quite a bit - can't be simpler, and programming is via an FTDI cable directly from the GUI.

Charles