Just in case the link vanishes I have copied the code here

Code:

long readVcc() {
  long result;
  // Read 1.1V reference against AVcc
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCL;
  result |= ADCH<<8;
  result = 1126400L / result; // Back-calculate AVcc in mV
  return result;
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println( readVcc(), DEC );
  delay(1000);
}

I found this clever little snippet of code that will return the supply voltage for the arduino using no external components! Would be great for those lipo projects !!!

http://code.google.com/p/tinkerit/wiki/SecretVoltmeter

Thanks for the input guys! So I guess the proper step here is to ask if anyone knows of some proper boards that are set up to be controlled instead of trying to find a hack that would make these cheap boards usable in that manner !

Are there any similar boards designed to be controlled for current/voltage from a micro controller signal?

Does anyone have any clever methods to modify one of these [url]http://www.ebay.ca/itm/1pcs-1-23V-30V-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-/110950894139?pt=LH_DefaultDomain_0&hash=item19d5304a3b&_uhb=1/url]to be able to control the output voltage from the arduino?

Or maybe there is a better way?

http://www.best-microcontroller-projects.com/capacitive-liquid-level-sensor.html

So indeed it is capacitance... A simple 555 circuit may work well here ! :-)

I found another system I suspect uses the same method... Looks to be more like a capacitance type system than a density based system as I had read in an article...

http://www.sailorssolutions.com/index.asp?page=ProductDetails&Item=TM03

The simplest depth sensor is using a tube sealed on one end, you connect an air pressure source ( hand pump etc... ) to the tube. Put air into the tube so that it just starts to bubble out the bottom of the tube, the air pressure required to displace this water will be the same pressure exerted by the height of water column displaced... Convert to height, calculate volume, the Freescale mpx10pd would measure approx 5ft of water depth.

Sorry it's not ultrasonic but this style of depth measurement is very common in industry!

What I'd you used this cheap sr04 sensors to find a location in the room ie the middle to make a pile ? That would be pretty simple?

I would imagine you will need to find a way to triangulate your position ... 2 fixed points of ir perhaps such as LEDs ... And a directional sensor ( tube on a receiver ) with angle measurements of some kind?

The better gps units such as gtpa010 are good to a few feet, might work for a leaf pile though?

So it turns out that my ftdi chip packed it in ... I suspect that it has been failing for a bit as I've had problems with that board! Too bad it took out a gtpa010 gps chip before it died!

I stumbled across an interesting sensor that I cant seem to find any information on. The way I understand it is that this strip sensor is applied tithe outside of a tank and the resistance changes as the level changes inside the tank... It says the resistance increases as level increases from 50 - 500 ohms. Somehow it can tell the difference in density inside the tank, supposedly works on propane as well...

http://www.rvgauge.com/products/model_709.shtml

Does anyone know anything more about this ?

1) To limit the current in case a wire became shorted etc ... ( breadboard )

2) After noting your comment I looked up your schematic and verified there are indeed 1K ohm resistors, however they are not pull down resistors, they go to the RX TX portion of the ft232rl chip. For this scenario to be plausible the ft232rl chip would have to ground the TX and RX portions of the chip which would put me close to explaining the current draw I found. This scenario however seems increasingly likely as putting the resistance below 1k would then put the data signal slightly about vcc/2 ...

3) As funny as you think your comment is, connecting a data line from a chip is no different ... other than the 3v3 is pulsed... and i need to verify that the current draw was what I suspected ... 5 ma is well within specs.

The other day I was playing with some serial communications from a GPS module and had resistors between the uart conections of the atmega328 and a gtpa010 GPS module and I noticed that the arduino would not receive serial inputs unless the resistor value was somewhat less than 1k ohm (i used 470ohm). I connected a 3v3 wire to the serial input Rx of the arduino and it read 5.5ma for a current! The FTDI chip on the arduino board worked fine with resistors at 2.2k ... (as high as i tested)

I suspect this number should be much lower than this! Is there some some setting for high impedance serial connections? Can someone explain why the current would be this high? How would i got about reducing the current?

For RPM you could also use an inductive signal from the ignition wire(magneto) (coil of wire wound around ignition wire clamped with a zener), coil wire primary circuit, alternator frequency.

using RPM would be a better way to tell when the engine has started ( rpm will come up plateau and then increase), or by watching for the starter current to drop off ( might plateau at 150 amps then drop rapidly as start the engine runs under its own power)...

Also just a side note all of those delays might cause you grief as your program gets more involved, look at the example "blink without delay"

I'm using some of those cheap eBay smps power supplies to drive a bunch of LEDs which are controlled via pwm with and arduino ... And I was wondering what is the best method to handle the power supply... Basically are caps good or bad? Bigger or smaller ...?

I haven't been able to find much info discussing the different considerations, but it seems like the ideal cap size is just large enough to reduce the ripple to an acceptable level, so small sizes around 10uf would be sufficient ( small sizes are effective because of the switching frequency) so are big caps bad or just unnecessary? I suppose large caps act like shorts until they are charged ... But they help absorb peak demands, however the power supply should generally be sized properly to handle that ...

Which leads me to another question, is there an ideal frequency ratio of pwm to switching frequency? I don't suppose they would get into some kind of weird harmonics ?

What are your experiences ?

By chance have any of you heard of this
http://m.tgdaily.com/software-brief/63065-microsoft-homeos-will-be-home-automation-of-the-future

Would a tcip ( LAN ) be a likely command interface? I'm looking to start building out my home
Network and compatibility going forward would be desirable ... It would seem that tcip would offer
The highest compatibility. Ie arduino with Ethernet shied ...