i was asked to use as much resources as possible

I don't think that this is what you where asked to do!. Go back and check!.

Mark

Yeah, maybe they meant these resources:

Peripheral Features
– Two 8-bit Timer/Counters with Separate Prescaler and Compare Mode
– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture
Mode
– Real Time Counter with Separate Oscillator
– Six PWM Channels
– 6-channel 10-bit ADC in PDIP Package
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Byte-oriented 2-wire Serial Interface (Philips I2C compatible)
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
– Interrupt and Wake-up on Pin Change

More specifically, PIR operates at around 10,000 nm, deep into the infrared, and IR
Leds/phototransistors work at 790-860 nm, at near infared. Our bodies can reflect
light at 800 nm, but don't generate light at those frequencies, just like we don't
emit visible light in the dark. Our bodies do generate heat at 10,000 nm.
[something like that].

There are actually 3 different types of IR proximity detectors - if we rule out PIR
devices, which operate on heat pickup and not light pickup.

The one type, which is normally called "IRPD" (ala your title) works at distances of
6-18", and simply signals yes/no. These use TV IR remote style pickup devices, which
operate at 32-56 Khz, and have built-in amplifiers and bandpass filters, so they have
100X the sensitivity of your IR phototransistor/diode [whichever it really is].
Yours is not an "IR/receiver", this is an IR receiver,
http://www.adafruit.com/products/157

The second type of detector is the Sharp IR ranger that joe mentioned. That variety
actually measures distance and gives an analog output vs distance.

Then, the 3rd type of detector is just for very tiny distances, eg under 1/2" or so, and
typically used for line detection in robots. Your devices would work for that. This
explains the idea,
http://forums.parallax.com/showthread.php/75940-How-to-Boe-Bot-Line-Following-with-3-QTI-Sensors

Cool. Interestingly, you're not the only one with such a classical relic on your hands.
Several are for sale on ebay. I'm kind of surprised.
http://www.ebay.com/bhp/core-memory

It would help to provide some links to the specific boards you have,
so people wouldn't have to guess.

What I would do [am actually in the process of doing] for home automation is not use the
2.4Ghz band for RF, but rather the 433 Mhz band with low-power transceivers. Where I live
I can pick up 30 other wifi routers.

So, a 433 Mhz transceiver in each room connected to whatever, and one central host for this
network. 5 mW transmit power at 433 Mhz can easily cover a house. Then the host only has
ethernet or wifi, and can connect to my router or main PC.

Although I am building my own pcbs for this, jeenode is one possibility for the remote nodes,
although the jeelib libraries and examples haves a lot of problems. Apparently, lowpower labs
has a better version of the s.w.

http://jeelabs.com/products/jeenode
http://lowpowerlab.com/

First, as DVDd mentioned, you'll want to add all kinds of filtering to the Arduino board, so
the automotive system noise doesn't blow the poor little Arduino's brains to bits. This is
a nontrivial problem [ie, requiring multiple lines of attack], so I won't say any more on that.

Secondly, I should imagine the battery voltage will sag 3-4 V or so when the starter motor
cranks, so you might use that to tell if someone is starting up the car.

Thirdly, although this will vary between cars, there must be 20 fuses that are powered up
only when the ignition key is turned on. Should be easy to find one and tap onto that.

Here is what you almost always need to do when buying from ebay.

1. Roughly 98% of the time, they don't provide adequate documentation, but the products
   are almost always clones of someone else's IP, and who do provide documentation.

2. so, what you need to do is use "google images" search, and try to locate the original
    device, where someone does provide the correct documentation. Then, you'll know
    what you actually have.

3. in regards PIRs, a lot of these devices already have an LDR inside that's used to adjust
    the ambient light sensitivity - but of course, first you have to know what the heck it is
    that you actually have. So, go to #2.

The reason why I'm confused is that I thought you could only measure voltage between to points and the potential difference between them. But the arduino measures at a specific point; the pin.

The Arduino ADC readings are always with respect to ground (being the 2nd point).

If you're not seeing the 1284 boards in the IDE, then the maniac1284 library is likely in
the wrong place.

It's not totally trivial to locate where the following page is found, but it indicates where
you are supposed to have the libraries located, namely in your sketch directory, and not
in your IDE directory.
http://arduino.cc/en/Guide/Libraries

The other thing is, when you uncompress the library zip files, they often end up one
subdirectory down too far, and you have to move them up - at least from my experience.

The other way to say this is, when you're reading only at the ends of a chain of Rs in series,
you're reading the equivalent resistance for the entire chain,

Req = R1 + R2 + R3 + ... + R20

and there is no way to tell what the individual R values are. Eg, they all can be 0 ohms
except for one of them, or they all can have the same resistance, &etc.

Simple arithmetic. The sum tells you nothing about the values being added up.

Bob, ya beat me to it by 1-minute. BTW, on another thread someone said the I2C pins are
not "fully open-drain" [or somesuch, whatever that means], so you cannot get I2C on a 5V
chip to talk to I2C on a 3.3V chip properly, or you'll overdrive the 3.3V pins. Do you know
anything thing about this?

It's very common with many e-bay sites that they clone other people's products, and don't
provide much tech support or documentation. They rely on the original designers for IP, so
if you look around a while using google search, especially in "images" mode, you'll find the
original products. Welcome to life in the 2010s.

Also, on that robot, it'll probably work better with a 6-cell AA pack [NiMH rechargeable], rather
than 4-cells as shown. You lose 1.5-2V or so in the L298 h-bridge chips, plus 4 cells will not
power your Arduino board very well either. You'll want to check the motor voltage rating, but
they'll likely take 5-6V ok.

Lost track of this thread. I've used the L298 in MW15 upright package in the past, and to
run over 1A, I always used a largish heatsink on it. They do run hot. As the chip is bipolar
technology, there is a 1-2V drop internally, so you'll get on the order of 1.5-3W per channel
of dissipation, up to 6W total.

Looking at the picture, I should think you could epoxy a goodly-sized heatsink to the
top of the chip.

Awww, actually I got my info from the windmeadow page,
http://www.windmeadow.com/node/42

Attach white to the Arduino's ground, red to 5 volt+, green to analog pin 4, yellow to analog pin 5. The nunchuck is only supposed to get 3.3+ volts. So far it has worked fine at 5 volts, but be warned. I am guessing that using the higher voltage will shorten the nunchucks lifespan.
..........
Consulting the chip's data sheet (ST LIS3L02AL), it looks like this could be caused by running it at 5V instead of 3.3V. It doesn't seem to do any harm, but you might get different readings at different supply voltages.

Also, note some of the comments in the Sparkfun page, so who knows? SF used to sell shields
that put 5V on SD cards too, so (I'm not sure they're experts either) ???
https://www.sparkfun.com/products/9281

Also, http://trandi.wordpress.com/2011/04/03/the-wiimote-and-fez-domino/

I figured I didn't want to blow up something I had just paid $20 for, so I used 3.3V, but I guess
you pays your money and you takes your choice, :-).