Interpreting the Duemillanove (2009) Schematics

I’d like to learn what the symbols and acronyms on the schematics for the Arduino 2009 mean so that I can better understand the whole thing. I’m looking at the schematic at http://arduino.cc/en/uploads/Main/arduino-duemilanove-schematic.pdf I’m hoping someone knows of a resource I haven’t seen yet that would help me figure some of this out.

An arduino glossary maybe? :slight_smile:

Some of it is pretty obvious and other things I can pick out by googling around. I’ve confirmed that USBVCC is where USB provides power to the arduino. I already know TX and RX to be transmit and receive so was able to come up with the LED and 1k ohm resistors related to that and the similar circuit on pin 13 that I’ve read about. GND and +5V are pretty clear also. The reset button on pin 1 of the ATMEGA8 is also pretty clear.

At this point it becomes a bit more shaky. USBDM and USBDP aren’t something Google’s really helpful on. What is the stuff in the upper-left of the schematic and how is it related? I’m assuming RXD and TXD are a digital transmit and receive? Why it has M8 appended sometimes I can’t tell. I’m assuming that all the white boxes are resistors. I’m not sure what the dual dark lines in the middle of a wire are. The solid black box in the USB power circuit, is that a capacitor?

Tons of more questions could be asked, but I think I’ve probably used up my quota. :slight_smile:

I’m assuming that all the white boxes are resistors.

Yes, that’s correct.

I’m not sure what the dual dark lines in the middle of a wire are.

Those are the capacitors. Note that they are labelled C1, C2, C3 and so on.

The solid black box in the USB power circuit, is that a capacitor?

No, that represents the fuse (the name F1 and 500mA rating gave it away).

Thanks for those pointers, very helpful to this newb. :slight_smile:

So F1 is the fuse mentioned in the USB Overcurrent Protection section of http://arduino.cc/en/Main/ArduinoBoardDuemilanove. I suppose I should have put that together. If I have my history right and am reading the schematics right, this would be the first time a fuse has shown up on an arduino schematic. Is that true?

And the Fuses and Capacitors are labeled F and C with a number to keep track of which is which so that would also mean that R is for resistor such as in the LED circuit on pin 13. Is their any logic to how they are numbered or is it just pretty much randomly as they were drawn?

Yes, R-numbers are for resistors. They are simply numbered as the designer wishes, either in the order they are drawn, or left-to-right on the diagram, or possibly in order of importance. There’s no significance to the number as far as the operation of the circuit is concerned.

Thanks,
Now I need to find out what all the acronyms mean. I think the datasheets are answering those questions.

I just found the FT232RL datasheet here: http://www.ftdichip.com/Documents/DataSheets/DS_FT232R.pdf and of course, the ATMEGA328 datasheet is on the arduino.cc description linked to here: http://www.atmel.com/dyn/resources/prod_documents/doc8025.pdf. The pin descriptions are turning out to be really helpful.

Hopefully, that will help someone in the future follow my path more quickly. :slight_smile:

Try this page:-
http://www.learn-c.com/schemat.htm

also try Googling:-
“How to Read a Schematic”

Thanks Mike. I found a few pages like that.

The problem I had with them was that they didn’t identify the majority of the symbols and acronyms on the schematic I was looking at, particularly the Capacitor and Fuse symbols. Just about everything they told me I figured out on my own. It isn’t hard to assume most of the symbols like the difference between a connection and lack of connection where two wires cross. Additionally, the traditional wavy line listed in all these resources as a resistor isn’t the symbol used for resistor in these schematics. The entire duemillanove schematic doesn’t have a single sharp wavy line, but several resistors exist.

Additionally, the traditional wavy line listed in all these resources as a resistor isn’t the symbol used for resistor in these schematics.

The wavy line is an American way of showing a resistor, the square box is the European way.
As to the acronyms don’t feel bad about not knowing them they just make them up (well mostly). Tx and Rx come from radio ham land, and anything that starts with USB is a signal that comes from the USB port.

Don’t feel you have to know them, I have been doing this for over 40 years and there isn’t a day when I don’t come across something I have not seen before.

Thanks Mike, I guess I’ve got a pretty good handle on it then. I’m going to try to take some notes and maybe will have a glossary to go along with those schematics some day. What’s the etiquette for adding a page like that to the arduino.cc wiki?

What’s the etiquette for adding a page like that to the arduino.cc wiki?

Well I would put anything out for peer review first. That is put it in the exhibition section and say you are thinking of adding it to the wiki and see what people say.

You could put it straight on but that is probably more polite. Content generated by someone who has just struggled to gain an understanding is often the most valuable, providing it is actually right.
Thanks

Thanks

Here’s a handy reference to some of the circuit symbols you’re likely to see:

http://www.kpsec.freeuk.com/symbol.htm

Thanks to Mike for finding that site!