Trying to make wall avoiding robot

Thread Starter

Qaptian

Joined Oct 27, 2008
37
OK, do this:
1) Open up the schematic in Eagle, and do an Erc (error check). Does anything show up?
2) Open up the board in Eagle, and do a Drc (Design Rule Check). This should give warnings if you have things routed too close to each other or overlapping.
For the Erc, only a few errors come up, the only important ones are POWER PIN IC2 VS connected to V+ and POWER PIN IC5 V+ connected to N$26, both of which look correct in the schematic. The other errors are complaining that something is unnamed or doesn't have a value.

The Drc is a little more scary, however. I come up with 270 errors, all but one are stop mask errors - these ones don't look too harmful, and the layer that they're on was necessary to make the PCB. The final error complains about the width of the copper pour I put on the bottom, but not the whole thing, just a single line that's near the edge of the PCB. I dismissed it because I thought it was an error in eagle, like when it complains that a part is missing a name.

I've since gone over the top part of the board - I can't see anything from above the components. I'll have to breadboard the circuit and hope that the problems go away.
 

SgtWookie

Joined Jul 17, 2007
22,230
OK.

On the BAT/+9V jack, you know that the side closest to the + is actually the negative side, correct?

Why don't you post your final SCHEMATIC so that I can see what it looks like? All I've seen for awhile is your boards.
 

Thread Starter

Qaptian

Joined Oct 27, 2008
37
OK.

On the BAT/+9V jack, you know that the side closest to the + is actually the negative side, correct?

Why don't you post your final SCHEMATIC so that I can see what it looks like? All I've seen for awhile is your boards.
Yes :). It's a bit of eye trickery there - the way that I soldered the header in required that I switch the wires to make the thing fit. The battery is connected properly.

One thing I thought of while poking the board with my multimeter is that the capacitors are far away from where they should be - I'm only getting about 5 volts on the actual battery when it's plugged in, then only about 3 volts on C4 and the 555 timer. Is there not enough juice to power the circuit? This could also just be my multimeter. I'm thinking I should move the capacitors closer to their components.

I've attached the schematic that I made the board from.
 

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SgtWookie

Joined Jul 17, 2007
22,230
You're probably getting such low voltage because you have a dead short somewhere.

You need to find the short and fix it.

You'll either have to start un-soldering things until the short goes away, or start cutting VCC traces. You can bridge the cuts by scraping off the coating on the trace, and soldering some buss wire across the gap.
 
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Thread Starter

Qaptian

Joined Oct 27, 2008
37
You're probably getting such low voltage because you have a dead short somewhere.

You need to find the short and fix it.

You'll either have to start un-soldering things until the short goes away, or start cutting VCC traces. You can bridge the cuts by scraping off the coating on the trace, and soldering some buss wire across the gap.
I think the PCB was messed up somewhere. The spare board that came with the original one gave me the exact same problem.

I've lost many of the parts and also gotten them mixed up, and some have been rendered unusable after my horrific attempt to desolder them for breadboarding, so I'm forced to put this project on hold.

I wasn't as ready for this project as I thought I was.

Thank you so much for your help, SgtWookie. It was extremely kind of you to walk me through all the hoops up to this point.

On to something not as difficult!
 

hgmjr

Joined Jan 28, 2005
9,027
From your schematic, I see that you have elected to use the internal RC oscillator as the clock source.

Just a word of caution when using the internal oscillator. It is not likely to happen but be aware that if the AVR is inadvertently programmed to use an external clock source, you will find that you will not be able to program the part in-circuit. You can recover from this snag by providing an external clock long enough to reprogram the AVR to use the internal clock again. The AVR are will appear dead but chances are good that is still OK.

hgmjr
 

SgtWookie

Joined Jul 17, 2007
22,230
It's best to start off with several kit projects. This was not really a beginner's project.

I know you really wanted to build this thing, but you went off with wild enthusiasm trying to get it done - and failed a number of times to ask for a "reality check".

It's not a simple project, no matter how you look at it. I can't troubleshoot it for you remotely, particularly because how "spaghetti-ish" the board wound up.

It looks good in the "virtual mockup." But there are so many problems electrically, I'm not willing to invest the time to troubleshoot them.

You ordered the board prematurely, without review. I had no clue you were going to do that.

Being a novice, you really need some guidance. At this point, I suggest that you purchase a number of kits and assemble them. They have instructions, schematics, and troubleshooting tips included. It's more or less a self-paced course.

Don't get discouraged at this setback. Setbacks happen. I know you learned a number of things; some of them were painful.

No pain, no gain.

Welcome to the wonderful world of plentiful coasters. ;)

Let's re-visit this topic down the road a year or so from now; once you have a number of kits under your belt.

It's definitely a do-able project. You just need to slow down a bit, and gain experience.
 
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