DC/DC step down coverter for breadboard

[displacedtexan]

I am trying to build a 2.7v power supply for my arduino on a breadboard.  I will be running it at 8 MHZ which should be fine at 2.7v.

Anybody have a favorite DC/DC converter IC that will work at 2.7v ish that is easy to build on a breadboard?  I tried to build a DC/DC booster on a breadboard and failed miserably.  I think it switches so fast that you really have to use a PCB or vector board.  I successfully built one of LadyAda's minty booster kits and it worked wonderfully.

I am hoping to power from a Lithium Ion battery which will run anywhere from about 2.7v to 4.2v.  I would just skip the DC/DC converter all together, but I am taking readings from an analog pin, and I think allowing the voltage to swing that much will really screw up the analog to digital converter readings.

Any advice would be greatly appreciated.

[Grumpy_Mike]

Anybody have a favorite DC/DC converter IC

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=152-524&x=0&y=0

I think allowing the voltage to swing that much will really screw up the analog to digital converter readings.

Not if you used the internal voltage reference of 1.1V, that would be independent of supply.

[borref]

I would just skip the DC/DC converter all together, but I am taking readings from an analog pin

If you power your sensor (pot-meter, LDR, ...) from the same DC source, your analog readings would still be ok.

[displacedtexan]

Not if you used the internal voltage reference of 1.1V, that would be independent of supply.

I did not even know that was an option!  Some google research shows that all I have to do to use the internal 1.1v reference is to put a capacitor between Aref and ground and put analogReference(INTERNAL) in my Setup loop.

So are there any other problems I might have running my boarduino variant straight from a Li-ION battery at 8 MHZ?

Thanks again for the help!

[borref]

So are there any other problems I might have ...

If you power your sensor from the Li-ION battery AND use the 1.1V internal reference - you will have an issue with analogInput.

If not, you will need to condition the input signal to stay between  0 and 1.1V for full resolution analog input.

[Grumpy_Mike]

you will need to condition the input signal to stay between  0 and 1.1V for full resolution analog input.

While you will get the full resolution between 0 and 1.1V you can quite happily input a voltage up to as large as the supply rail. If you want something higher than 1.1V but independent of supply voltage you can use an external voltage reference and feed it into the Aref. Switch over to theis in software first.

[borref]

While you will get the full resolution between 0 and 1.1

True, it wasn't a good choice of words on my part. However, analogRead will not be able to discriminate values above AREF/1.1V (they will all read as 1023).

As long as your choice of AREF (e.g. Vcc) is tied to the voltage reference of your sensor, analogRead is fine, even if the reference itself is changing. So powering directly from a battery (bypassing the regulator) may not have ADC issues at all in the default configuration.

If your sensor on the other hand is ratiometric to some other independent reference, you will have problems unless your choice of AREF remains fixed or ideally use the very same reference (never above Vcc however) for its ADC conversions.

For someone powering his Arduno from a battery, it seems likely that attached sensors will be powered from the same source and typically these sensors will output a signal ratiometric to supply voltage. If this is the case, and using the 1.1V internal reference, analogRead levels will be influenced by a drop in battery voltage.