LM324, LM358, other?
It will be for a photodiode amp circuit.
Thanks.
The op amp LMC6484 is a CMOS op amp for power voltages up to 15v. Its input current is so small that it is vanishing. Its output swing is "rail to rail", according to its data sheet. I use it for sample and hold .
Input current 0.00000000000002 Amps !!!!!!!!
I've seen LM358's mentioned, have a few in fact, but they don't have a particularly
great spec (you won't get to +ve rail and it can't pull down to ground with more than a few microamps).
I did some research for an audio project and found the (rather expensive) AD8656 which has
some excellent specs for a rail-to-rail 5V device, in particular very low offset voltage, ultra low noise,
good bandwidth and settling time, and can drive extremely close to the rails at 1mA current level.
The LM324 is in a nice quad package... but is it any good? It's sort of like saying that Skoda* makes a great sports car. No, I think Skoda really only makes a "car" and saying they are great might even be more than some are willing to say. The LM324 is just a cheap affordable "car" of an op amp. If your demands/requirements are not too specific... it's probably OK. If you want real performance and low noise/offset you sort of have to take the LM324 off the list.
Note: all based on my experiences... so other can surely disagree with me... I don't mind.
*or pick any low end affordable car maker... today I pick Skoda, I could have said Tata (nano)?
Most common would be the LM358, there is one on every Arduiono board that has autopower select 8)
Only used as an open-loop comparator tho.
There are better parts, parts with voltage swing that is much closer to rail-to-rail, parts with faster slew rates, parts with better drive capability, parts with better rejection of power supply noise, parts with quiet input stages to not impact your signal.
What you select really depends on what you want to do with it.
Thanks for the replies.
I'm looking at this circuit (my application has nothing to do with doors though) 
http://www.npeducations.com/2013/01/laser-light-based-door-opener.html
The op amp in this case is used as comparator, I could probably do away with this and feed the output of the transistor to the arduino and do the same in software?
Yes.
Can be made simpler. Take the input into base of T1 and work from that. Will vary from ~0V with no light, to something higher when there is light. analogRead() and away you go...
Lakes:
Thanks for the replies.I'm looking at this circuit (my application has nothing to do with doors though)
http://www.npeducations.com/2013/01/laser-light-based-door-opener.html
The op amp in this case is used as comparator, I could probably do away with this and feed the output of the transistor to the arduino and do the same in software?
Or use the analog comparator on the ATmega itself?
Can't - one half is wired up for voltage detection, the other half is wired to drive the onboard LED.
It is sloppy practice to use an Op Amp where you need a comparator. Op Amps may draw excess current. That does not mean you can't (the biggest limitation is slower switching times), but in practice, there is no one all-purpose Op Amp.
I strongly recommend downloading the PDF of the 2nd edition of Op Amps for Everyone:
http://www.ti.com/lit/an/slod006b/slod006b.pdf
Or buy the latest 4th edition on Amazon. Lots more info, especially regarding the downsides of using an Op Amp as a comparator.
In any case, I like the proposed solution of just using the Arduino to detect the level.
polymorph:
It is sloppy practice to use an Op Amp where you need a comparator. Op Amps may draw excess current. That does not mean you can't (the biggest limitation is slower switching times), but in practice, there is no one all-purpose Op Amp.
Also good comparators are dirt cheap anyway....
What makes a comparator good is not the same as what makes an op-amp good (some op-amps
draw significant current from their inputs when they are separated by a volt or more, since this is
the unusual case for op-amps)
And there is really no such thing as a rail-to-rail output Op Amp. I think someone already mentioned that you can only draw microamps when getting close to a rail.
I've been doing Op Amp classes at OlyMEGA, a maker's club in Olympia, WA. I'm about to do one on adapting a silicon diode as a temperature sensor, by turning the about 0.5 to 0.7V -2mV/C into a positive going 0 to 1.1V signal. Since 0V is 0C, it is important that the output remain linear and reliably go down to 0V, not just down to 20mV or so. I have found that this is nearly impossible with a single supply Op Amp. I've tried a few tricks, including adding a diode between the Op Amp and the output load, and they just fail to operate linearly near 0V.
So in the end, I'll use an output from the Arduino to work a diode/capacitor charge pump inverter to create a -2V rail (using an LED as a crude zener-type regulator) that the Op Amp and output load are connected to. I could probably find a suitable Op Amp and configuration that would work with a single supply, but for the purposes of this class, the circuit needs to be simple and use a relatively cheap Op Amp. With an LM358 and a low current negative supply, I can do this.
I will, of course, have a resistor between the Op Amp output and the Analog Input pin on the Arduino to save it from below freezing temperatures.
Of course, if this were meant for something like a room thermostat, I don't need to measure down very low, so I could get away with a single supply.