does an ICs input voltage have to be regulated or can one just hook without one?
and does anyone know a good source where i can find tutorials on how to understand the IC datasheet.
thnx in advance.
cheers
The majority of IC's need a stable powersource to function properly.
This is all dependent on the function and use of the IC.
I would advise you to read a lot about basic electronics and principles.
On the net there are loads of tutorials etc.
This way you can gain knowledge about electronics and recognize the specs that are use in the spec. sheets of IC's.
Unfortunatly there is no shortcut to obtain knowledge 
Happy reading...
U should try it without regulated and see if it works accuratly and well, sometiems its fine and sometimes what you have is enough, just don't forget about it if you are getting glitches that its one possibility to check
U should try it without regulated and see if it works accuratly and well
Instead of just trying and watching what happens, I strongly suggest that you take the time and learn to read the datasheets. It you power the chip from out of the range or unstable voltage, it may seemingly work for a while, but can damage the chip and stop working if you do a slight change in the configuration.
If you post here the IC's part number and link to the datasheet, someone here may even help you to interpreter the datasheet.
Hmm, so let's take an example. ATMEGA328P-PU running on 3 AA's and no regulator. Is there something in the data sheet which advises against this? I couldn't find it, but since we're on the topic I thought I'd ask.
Power from AA batteries is inherently more stable that what you get e.g. from a wall wart. An unregulated nominally 12V wall wart may provide several volts more when the load is very low.
Section 28 (I think) of the data sheet has a chart showing the acceptatble voltage for operation at different clock frequency.
Earllier it has a chart showing Hi/Lo voltage at different current levels wlth different Vcc levels.
Reading the chart, you fill 16 MHz operation at 4.5V is well within the acceptable range for both voltage level and frequency.
Just about any switching regulated wallwart will work fine also. www.dipmicro.com carries several at 4.5V & 5V at different current capacities to support your arduino and the external loads. Or go slightly higher (7.5V) if you want to plug into the barrel jack vs connecting to the 5V & Gnd pins on the power header.
U should try it without regulated and see if it works accuratly and well, sometiems its fine and sometimes what you have is enough,
Rubbish. You always need to use capacitors. Take that as a rule and you won't ever go wrong. The occasions where you might think you have "got away with it" are illusory and often short lived.
Why is it that beginners on this forum are afraid of capacitors? They cost next to nothing and are vital for a stable noise free supply.
Grumpy_Mike:
Why is it that beginners on this forum are afraid of capacitors? They cost next to nothing and are vital for a stable noise free supply.
Why do people drive an automobile fast before they have mastery of how it operates? Because it is easier and (seemingly) faster.
I learned to drive quite late in life compared to most people, when I was 21 (I had some classes in high school - but I didn't do well, except on the freeway, strangely). My (now) wife taught me when we were dating. She taught me on dirt roads that were around her house out in the desert here in Arizona. She told me to take the car up to 25 mph. I had never been in a car with a tach. I don't think she'd ever driven at 25 hundred RPM on a dirt road, either...
Grumpy_Mike:
U should try it without regulated and see if it works accuratly and well, sometiems its fine and sometimes what you have is enough,
Rubbish. You always need to use capacitors. Take that as a rule and you won't ever go wrong. The occasions where you might think you have "got away with it" are illusory and often short lived.
Why is it that beginners on this forum are afraid of capacitors? They cost next to nothing and are vital for a stable noise free supply.
can u please explain why is it better to attach caps to the regulator. i have read that its "better". no one explains why.thanks in advance
Regulator spec says so:
"It is not necessary to bypass the output, although this does improve transient response.
Input bypassing is needed only if the regulator is located far from the filter capacitor of the power supply. "
So puta 0.1uF on the output, make your circuit happy.
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000447.pdf
Look at all the varieties of things you can do with a 3 terminal regulator here - and all have caps.
Hmm, so let's take an example. ATMEGA328P-PU running on 3 AA's and no regulator. Is there something in the data sheet which advises against this?
An AA battery gives you 1.5V so normally you have 4.5V but when they are very fresh you might get 1.8V from them so that will be 5.4V.
Now look in the data sheet at section 28, and see the absolute maximum operating voltage. This is the voltage you must not exceed. It says 6V so you are OK. Now a battery running down might go to 1.2V so this would give you 3.6V to work from.
Section 28.2 shows you the recommended operating range 1.8V to 5.5V so again from that point of view you fine.
However, section 28.3 shows you that the maximum speed of the clock is related to supply voltage, so you then have to plug in your systems clock frequency and see if it will run at the range of voltages you want. It looks like this is the limiting factor for your design decision of using three AA batteries.
Grumpy_Mike:
Hmm, so let's take an example. ATMEGA328P-PU running on 3 AA's and no regulator. Is there something in the data sheet which advises against this?
An AA battery gives you 1.5V so normally you have 4.5V but when they are very fresh you might get 1.8V from them so that will be 5.4V.
...
However, section 28.3 shows you that the maximum speed of the clock is related to supply voltage, so you then have to plug in your systems clock frequency and see if it will run at the range of voltages you want. It looks like this is the limiting factor for your design decision of using three AA batteries.
Thanks... Yeah, I have measured this extensively, and thought I had everything figured out. But then I saw this quote, "The majority of IC's need a stable powersource to function properly...Read the data sheet" So I wanted to make sure I didn't miss something, because AA's didn't exactly seem like a 'stable' power source:
Capacity Test - 2AA @ 13mA by maniacbug, on Flickr
Most of my use now is 2xAA's, and it looks like 8MHz is the sweet spot for 2.4V. Although in my test above, the unit was still operating fine at 1.8V with an 8MHz crystal before the BOD kicked in.
Nice graph although the title should say "Voltage" not "Capacity"
"The majority of IC's need a stable powersource to function properly.
I think that context was about regulated wall wart type supplies. Batteries are stable over the short term, it is just the long term where they drop off. Batteries are like us they are always going to die, it is best to make sure they do it with dignity.
Grumpy_Mike:
Nice graph although the title should say "Voltage" not "Capacity"
Thanks. Indeed, I suppose that is true. My goal was to measure capacity, so the answer was 13mA * 158h = 2054mAh, not quite the 2300mAh the batteries were rated at.