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[on:]

I need to generate a precise 5v on my Arduino Uno board.  I know the onboard regulator isn't very precise, and I've measured too much variation between the 5 different Uno boards I have.  So how should I go about it?  It seems like most precision voltage references need at least 6v so it can regulate it down to 5v.  So do I need to use a DC-DC boost converter to boost the onboard Uno 5v up to something like 9v and then use a reference IC to generate the precise 5v?

[Reply #1 on:]

Why not just get a switching 5V regulator? Then you won't see any variation.
http://www.dipmicro.com/store/DCA-0510
http://www.dipmicro.com/store/DCA-0520
Or get 6V, 7.5V if  you want to regulate it down yourself. Maybe use an LM317 with a trimming resistor (10 turn potentiometer) to get it right at 5v.

[Reply #2 on:]

Standard approach to this is take a sufficiently accurate voltage reference chip (and maybe a precision op-amp to scale/buffer the output).  Won't give a power supply but will be a voltage reference for an ADC for example.
 
If the application is analog->digital conversion there are many ADCs with built in references.

But without knowing the specification can't really suggest any concrete examples.

[Reply #3 on:]

I need to power some pressure sensors that require a stable 5v excitation voltage.  The sensor outputs an analog voltage that's proportional to pressure being exerted on the sensor.  Currently I'm using the the ADC of the ATmega328 to sample the sensor output.  Eventually I'll probably use a separate ADC chip because I want better than 10-bit resolution.  Each sensor draws about 5ma, and I could have up to 5 sensors on one board.  So if I could find an ADC chip that provided a 5v reference capable of supplying enough current and could read a voltage from 0 to 5v, then that would solve my problem.

[Reply #4 on:]

Are the sensors not ratiometric?  By this its meant that the ratio of the output voltage to the supply voltage encodes the value, not the absolute output voltage.

[Reply #5 on:]

yes, but I'm using a precision 3.3v regulator as the external reference voltage for the Atmega328, so if the 5v excitation voltage varies, the output of the sensor compared to the stable 3.3v varies as well.

[Reply #6 on:]

So use  the 5V 1A switching regulator, will be a very stable 5V source for your 25mA plus the arduino's 30mA.
Use the analog devices SPI ADC that's been posted previously with 6 sample & hold inputs & get 6 conversions at the same time.

[Reply #7 on:]

So use  the 5V 1A switching regulator, will be a very stable 5V source for your 25mA plus the arduino's 30mA.
Use the analog devices SPI ADC that's been posted previously with 6 sample & hold inputs & get 6 conversions at the same time.

Do you happen to know the part number of that ADC?  I've been searching for days and haven't found one with 0-5v input and multiple channels.

[Reply #8 on:]

Might have been this one
http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7656/products/product.html
You can search/filter at analog.com to find others also.

[Reply #9 on:]

That looks great, thanks!  There are so many ADC chips out there that I've had a hard time trying to figure out which one to use, but that one seems like a good one to start with.

[Reply #10 on:]

I've had my eye on this one for awhile, but holding out so far.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390106010150&ssPageName=STRK:MEWAX:IT

And another:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230619695873&ssPageName=STRK:MEWAX:IT