most simple arduino

Hi all,

I have made two different boards, one is working when powered off the ftdi cable, one is not... So the question is what is the most basic arduino one can make when powered from an ftdi cable? I have the reset cap (and pullup) and vcc, gnd, tx and rx. the chip has crystal an caps for it. Do I need a decoupling cap with my setup? i have room for it, but I don't have the cap on hand. It is also only on the regulator side of the power selection, so it won't come into play when the jumper is set on usb power. What am I missing? There is 5v where it should be, but even preprogrammed chips won't flash my led, so the chip can not be working with my setup.


Do I need a decoupling cap with my setup?

I would say always yes.

Have you got a system that doesn't work?

I would look first to see if the crystal is oscillating, the the input pin is high and that BOTH 5V and BOTH grounds are connected. The other thing to check is the two capacitors on the crystal are the value the crystal is expecting.

The other thing that might be wrong is the fuses inside the chip. These have to be set up for an external crystal oscillator. Try the chip in a known working arduino board.

Perhaps this would be a good reference if you haven't seen it yet:

Thanks for the quick replies.

The chip is working and can be programmed by any other working board. The 16MHz crystal has its 22pF caps. How do I check if the crystal is oscillating?


How do I check if the crystal is oscillating?

Well you need an oscilloscope, it electronics it is your eyes and it is difficult to do anything with regard to fault finding without one.


Thanks, I needed that in writing. I wil now show my wife...


Before the newly ordered scope is in the mail (!), I have another question: Is the distance from the crystal to the 22pF caps of importance? The board itself is not very big ( smaller than the 2009), but very crowded. The caps are probably two inches away from the crystal.


Yes that sounds like a long way off, they should be mounted as close to the crystal as possible and the crystal should be mounted as close to the processor as possible. This is because lengths of track act as inductors, the higher the frequency the more significant is the parasitic inductance.

When I make anything the crystal is always the first thing I mount.

Thanks again, this solved the issue. I had some oscillators lying around, and when i cut the 22pF caps and replaced the crystal with one of these, it worked just fine.

Thanks again!