questions on first pcb attempt

[ozbot]

I am in the process of making my first pcb, for the $50 bot.

I have two questions:

1.  Below is what I have made so far, using ExpressPCB.  How wide do I need to make the tracks and do I need to make them that wide back to ground? (or is it not an issue on this scale?)

2.  Can the ground of two different battery's be linked? Should this be avoided?

[roshan.r24]

1.  Below is what I have made so far, using ExpressPCB.  How wide do I need to make the tracks and do I need to make them that wide back to ground? (or is it not an issue on this scale?)

Hey ozbot  your layout looks nice but is it complete yet?
I see quite a few connections which im guessing you want to make using wires.
Also, just wanted to know what programmer you re using since i saw a 6 pin connector.
As for the thickness of the regular tracks and the ground track you can have a width of around 0.04 or 0.05 inches. That should be fine. I recently finished my 50$ bot pcb. ive posted my layout and some pics too.
check it out. it might help: 
http://www.societyofrobots.com/robotforum/index.php?topic=8821.0
ive made all my tracks 0.04in wide.

2.  Can the ground of two different battery's be linked? Should this be avoided?

Are you talking about using the battery holder and the 9V battery together?
This is from Admins tutorial:
"This is the slightly modified schematic for battery holder users. The blue circles with a red dot in the center represent the 4.8V, while the red only dots represent the 9V battery connection. All this means is that the servos use power from the 4.8V pack (which can supply a lot of power), while the sensitive low power electronics use the regulated voltage from the 9V battery. Remember that all grounds need to be common"

The common ground completes your circuit. So, yes you have to connect the grounds of both your batteries.

Hope this helped 

[SmAsH]

the only problem i can see is the non-common ground... correct this and it should be fine.

[Soeren]

Hi,

No reason for such narrow tracks. widening the tracks will help you avoid breaks from pinholes (and save the environment from the extra copper).

[benji]

Nice PCB ...
its a good idea to widen the Vcc track but to take advantage of that you should widen the Gnd track too.
Im not sure where is the GND in your circuit.

[Razor Concepts]

Just a note - the two ground pins on the microcontroller are not connected in that layout. I read it is good to connect them anyways, but is the internal connection good enough?

[SmAsH]

theres an internal connection?
i find its good just to connect them anyway, for that piece of mind...
its just one more trace...

[ozbot]

Hey ozbot  Smiley your layout looks nice but is it complete yet?
I see quite a few connections which im guessing you want to make using wires.
Also, just wanted to know what programmer you re using since i saw a 6 pin connector.

Except for a mistake or two in the pic, pretty much done bar the sizing (& mabye some pcb art....), a few wires & components to go topside over tracks, yes.I am using the AVR ISP mkII, with AVR Studio.  Yes, it uses 6 pins and 2 power sources, 9v and 6v.
Hope my board comes out looking that shiny.....

the only problem i can see is the non-common ground... correct this and it should be fine.

I built my first stripboard according to this
http://www.societyofrobots.com/robotforum/index.php?topic=3292.0
and it works.  I remember thinking about ground regarding two batteries while constructing, but failed to grasp until I look a little closer that they are common through the  mcu, no?

its a good idea to widen the Vcc track but to take advantage of that you should widen the Gnd track too.

Was wondering about the gnd width....

Anyways, I will widen my tracks a bit & make a better common gnd. Cheers

[SmAsH]

do a test, get out your multimeter and see if there is a connection inside the chip...
if not, make a hard-connection on the outside...

try and get your tracks as wide as possible, better to be safe than sorry, especially with servo power buses.

[Soeren]

Hi,

do a test, get out your multimeter and see if there is a connection inside the chip...

That's heading for disaster - never ever put an Ohm-meter (or continuity meter) on a chip like that, consult the datasheet instead.

[sonictj]

there is no internal connection one is gnd and the other is agnd.  The datasheet would not suggest connection them through, I believe a low pass filter via an inductor, if the connection was already made.  The purpose is to decrease noise for the ADC.