Using Oscillator as a Crystal

Using Arduino General Electronics
1

I'm trying to get my ATMega328 off the Arduino board and onto a breadboard. I know I need a quartz crystal (the small oval with 2 leads) between two of the pins. However, all I have is an oscillator (a large rectangle with 4 leads). Is it possible to use the oscillator as a crystal?

2

cubemike99:
I'm trying to get my ATMega328 off the Arduino board and onto a breadboard. I know I need a quartz crystal (the small oval with 2 leads) between two of the pins. However, all I have is an oscillator (a large rectangle with 4 leads). Is it possible to use the oscillator as a crystal?

Yes, but it requires changing one of the fuse byte bits that control clock type/source.

3

Yes, just run the oscillator output to the XTAL1 pin and leave the XTAL2 pin unconnected. The oscillator will need +5V and GND, and a decoupling capacitor between the two will help. You will also need to use the ISP connection to reprogram the fuses to use an external oscillator instead of a crystal.

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The Basic Motor Driver: simple, inexpensive motor driver for 1 stepper motor or 2 DC motors

4

Hmm, thanks. But does that mean there's no way to do it in the Arduino's default AVR mode?

5

By "default AVR mode" do you mean the default fuse settings? Good question...officially, you're supposed to change the fuses depending on the clock source, but I'm wondering if it just might work to leave the fuses the way they are. I think it's worth an experiment. The worst that could happen is you damage the clock circuitry on the Arduino and a) it fails to work at all, or b) it will never work again using a crystal. Either way, with a DIP microcontroller that can be swapped out it's a pretty inexpensive experiment.

Personally, I'd buy a $30 AVR-ISP and have something that is known to work :slight_smile: I use my AVR-ISP so often that the $30 has paid for itself many times over.

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The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins

6

Prices have crept up some - AVR ISP MKii now $33 at Mouser (just bought one).
Does work nice for looking at fuses tho.

7

RuggedCircuits:
By "default AVR mode" do you mean the default fuse settings? Good question...officially, you're supposed to change the fuses depending on the clock source, but I'm wondering if it just might work to leave the fuses the way they are. I think it's worth an experiment. The worst that could happen is you damage the clock circuitry on the Arduino and a) it fails to work at all, or b) it will never work again using a crystal. Either way, with a DIP microcontroller that can be swapped out it's a pretty inexpensive experiment.

Personally, I'd buy a $30 AVR-ISP and have something that is known to work :slight_smile: I use my AVR-ISP so often that the $30 has paid for itself many times over.

--
The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins

Is this something I could also use to upload sketches and burn the bootloader?

8

Absolutely, that's what makes it so useful.

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The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

9

link=topic=94734.msg711461#msg711461:
Yes, just run the oscillator output to the XTAL1 pin and leave the XTAL2 pin unconnected. The oscillator will need +5V and GND, and a decoupling capacitor between the two will help. You will also need to use the ISP connection to reprogram the fuses to use an external oscillator instead of a crystal.

--
The Basic Motor Driver: simple, inexpensive motor driver for 1 stepper motor or 2 DC motors

I've done something like this before, but put a 1k resistor in series to be safe ( a superstitious precaution perhaps )