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home brew arduino

Hi All,

 I am trying to build a home brew arduino, the drawing off the site calls for a 100nf or ,1uf I don't have one on hand can I use a larger cap?

Also is there a substitute for the 22pf on the crystal?

arduino-duemilanove-schematic.pdf47.36 KB
arduino_pic_001.jpg246.41 KB
arduino_pic_002.jpg368.93 KB

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Hi I have another question, and its due to my struggle reading prints I think, at the top of the following picture is the plug I want to put into my arduino, I got ground and vcc as well as rx and tx, does the reset and cap go on cts or dtr? I want to customize my arduino to fit my plug.

my plug is differant than the one showm it is as follows



Making this has been fun, hopefuly it will help me understand it better.



Scroll all the way to the bottom to see the circuit, you will notice that DTR is connected to the RST of the Arduino. :D And CTS just makes like a tree. :) Hope this helped.

Regarding uploading...

"Minimal Circuit (Eliminating the External Clock)

If you don't have the extra 16 MHz crystal and 18-22 picofarad capacitors used in the above examples, you can configure the ATmega328 to use its internal 8 MHz RC oscillator as a clock source instead...."



"Why 22pf capacitors for crystal oscillator?" post...



Concerning the accuracy of the 16MHz crystal with "standard" 22pF caps...

"... I don't have a lot of faith that the caps associated with the arduino are properly sized; there's a sort of "standard" to plunk down a crystal with a couple of 18 or 22 pF caps, but apparently if you want to do it RIGHT, it's a bit more complicated than that (and you'd need the crystal data sheet to start with.)  OTOH, I've never much cared about higher accuracy than needed to make serial com work, so I haven't been overly motivated to track anything down..."


I have the 22pf caps in ceramic coming from china, I am pretty lucky usualy only 2 weeks for me, can ny one direct me to a tutorial or explanation of what each part of the arduino circuit actualy does, I would like to use a ftdi to progran this so I know I do not need all of the circuit but I am not sure what I can omit


It's oriented towards the Uno and doesn't include the timer but it should teach you what you need to know.

There was only 1 100nf in the schematic and it was on the 232 part of the circuit. Easy answer, if you don't need the USB Uart as part of the circuit (that is, if you already have a functioning Arduino and can use it to program the chip) then don't waste time with that part of the breadboarding process.  Yes, you need the 22pf caps on the crystal.  The exception is if you use a resonator, which isn't as exact as the crystal but should be good enough for most applications.

You will have to use 22pF capacitors for the crystal otherwise the clock will not work. For power decoupling capacitors, yes in some cases you can use larger values.

However where a 100nF is specified you should still use a monolithic ceramic as they are much better for high frequency noise filtering. If for example you used a 1uF electrolytic capacitor then despite being 10 times bigger it still would not filter the high frequency noise very well.

You must remember that even your MCU generates a lot of noise and those filter caps protect it from itself as much from outside noise. I built an Arduino on a breadboard once and it would not work until I added the filter capacitors.

The only 100nf cap I saw in it was on the USB converter.  Gareth's tutorial on converting a cheapie model used a .01 μf across the reset if I remember right.  I don't think you'll do any damage by substituting what you have-it will either work or it won't.

that the 22pf caps for the crystal are fairly specific to my knowledge. You could always just use the internal oscillator, if you don't need terribly specific timing. That would gain you a pin or two and save 3 components.