First Circuit Schematic - please look over

[cjwillms]

I'm a newbie to circuitry, and I need a bit of help. If possible, please look over my schematic, and tell me if you notice any errors. The whole thing will be built on a breadboard, mostly just for experimentation. I'm really just trying to understand the basics of circuitry design, by controlling a few LEDs and a servo motor.

http://img151.imageshack.us/my.php?image=firstcirucit6wt.jpg

Any suggestions would be appreciated.

[Afroman]

First schematic eh? You might wanna stick to something simpler then
Anyways your LED bank is looking good.
I don't think you are meant to connect XTAL1 and 2 to ground.
Your cap C1 is incorrectly wired. It needs to go in parallel with VCC and GND

[cjwillms]

I could do simple, but then again, complexity is fun! Lol, anyway, thanks for the suggestions. I went ahead and fixed the errors.

[Admin]

Hmmm yea I dont think xtal should be connected to ground either, what does the atmel manual say?

As for the LED's . . . I calculated only 7mA not 10. Do the LED's you are using work with just 1.4mA current? You may or may not want to reduce the resistor sizes.

As for the cap, you probably want ~10mF, not 10uF (and in parallel with ground as Afroman said). But it depends on your power source and amount of current your servo will drain too.

[cjwillms]

According to the manual, Xtal1 is the input for the internal crystal, and Xtal2 is the output from the internal crystal. I just figured that since Xtal2 was sending out a signal, connecting it to a GND wouldn't hurt it.

Truthfully, the LEDs confused me. I bought them from here and I really don't know much power they draw. I used this article for guidance, and they mentioned that there 3mm LEDs produced a 1.4v drop, so I figured mine would be around it as well. If not, 7mA is plenty.

I'll be running everything off a 5v power regulator. According to one of the articles on your site (here)

Capacitors can also be used to prevent power spikes that could potentially fry circuitry. Next to any on/off switch or anything that that could affect power suddenly should have a capacitor across it.

Capacitors can improve efficiency and longevity of electric motors up to 100%. Place a small ceramic capacitor of like 10uF across the two leads of your motor. This works really well with el-cheap-o motors. Not much effect with high-end expensive motors however. These capacitors will also signficantly reduce EMI (Electro Magnetic Interference) and system noise too.

10uF seemed reasonable to me. It's really just there to help prevent EMI. The Voltage regulator should stop most surges, and I'll be running off a battery so I shouldn't have any surges.

Anyway, thanks for the suggestions.

[Admin]

But you forgot an additional capacitor for power . . . One small cap for EMI and the big cap to make sure you dont have sudden power drops - the voltage regulator can only handle surges. As for servos, you do not need the small EMI cap as it already has its own circuitry.

Get a capacitor that is rated at least twice the voltage you expect to go through it. Have it rated at 1mF-10mF for every amp required. For example, if your 20V motors will use 3 amps, use a 3mF-30mF 50V rated capacitor.

Your servo will probably draw only half an amp, so you will probably just need ~.5 - 5mF rated at about 10V+. Getting a bigger cap wont hurt, it will just take up more room on your circuit board.

[cjwillms]

I see your point. I'll probably put in a larger cap, but I can't do anything right now. I had ordered the parts I needed today, so I still have to wait a week :/ . I'll probably rip up a bunch of old computer stuff for some spares, but that's about all I can do. If all goes well, I should be able to build my first robot (walker type). The only other thing I'll really have to worry about will be the sensors and funding, but that shouldn't be that bad.

[Admin]

This kind of cap is real common in old electronics, shouldnt be hard to find one.

A walker, eh? You really did choose the hard path! 

Good luck!

[cjwillms]

I don't think it'll be too bad. It'll just time some time and funding. As of right now, I have a $150 part limit. I can probably make due with that, but the chasse of the bot will probably be made out of bent up paperclips or similar. I can handle everything in the programming sense; I really just need to learn a bit more about sensors.

The overall design would probably be meant to look kind of like this
http://www.brickshelf.com/gallery/SaberScorpion/Mechwarrior4/newdaishi1.jpg

It's a good design in my eyes, and it really shouldn't be hard to figure out the mechanics of it. I'll build the legs first, and try to incorporate a few IR sensors into the legs, in order to avoid collision and prevent falls. Hopefully, it’ll be able to navigate around a room with hitting anything.

If money wasn't an issue, I’d probably have a microcontroller in each appendage, controlling motive functions and the sensor for that part. I would then have a full computer (motherboard, cpu, ram, and a solid state hard drive) as the main controller. The basic idea, would to have a true digital camera in the head. The camera would take a picture, upload it to the computer, and then the computer would process the image, applying image reorganization. From there, if the bot wanted to move, it would forward the command to the microcontroller. The microcontroller would then perform the command until the main computer tells it to stop, or one of its sensors tells the microcontroller it's not safe.

It is possible, but very complicated and it would cost a ton.


Anyway, I'll have about 3 months of free time during the summer, so I'll get a good bit of work done on it. I'll try to a progress report, whenever I start to show some real progress.

[Admin]

I emphasize to keep things simple. If you have a choice between a really cool but complicated idea, and a really boring but much simpler to do idea, I press you to do the second. I had too many ideas for my first robot and it came out as a complete and total failure. I wasted months and hundreds of dollars on it. I wanted to do too much, and I knew too little.

Anyway, you probably want to use aluminum and HDPE for your chassis. Both are super cheap, ultra light, and easy to work with.
http://www.societyofrobots.com/materials_aluminum.shtml
http://www.societyofrobots.com/materials_hdpe.shtml

Also, since walkers require very light weight frames, look into carbon fiber too. Its a little harder to work with though.
http://www.societyofrobots.com/materials_carbonfiber.shtml

And a little side trick, put all your heavy stuff as low as you can so your bot wont be top heavy - for example, put the batteries in the feet.