Hi all,
I just want to use an amp as in inverting amp to amplify a signal from a photodiode. Ive been advised that LM741 is just outdated and its really only for +-15v applications.
Since the board is 5V.... What op amp should i purchase - theres so many to choose from. I just need a general op amp which will do the job.
View page 2 for more detailed description - sorry for lack of detail
Use a LM339 quad comparator.
Or a LM3900 norton opamp
http://www.ti.com.cn/cn/lit/ds/symlink/lm3900-n.pdf
Would it be good for something like this?
Do you want 0 to +5 volts swithching as the output? i.e. Digital
See figure 25 and 26 in the 339 data sheet for 0-5V o/p
Honestly not sure what i need - but i guess i could measure photocurrent and id imagine id need ground and 5v
Id like inverting amplifier with negative feedback.
The applications in sheet dont really look like what i have in mind, plus i dont really understand them, pretty new to this
MrDropsy:
Honestly not sure what i need - but i guess i could measure photocurrent and id imagine id need ground and 5v
If you say what you are trying to do then we can tell you what you need.
MrDropsy:
Id like inverting amplifier with negative feedback.
Why?
Your application is the key. Are you wanting to detect or measure?
DO NOT CROSS POST
http://forum.arduino.cc/index.php?topic=276690.new#new
The problem is there are about 20 important parameters for an opamp, so thousands of
device lines are available.
Do you need
fast response?
low noise?
low offset voltage?
low input current?
low power consumption?
true rail-to-rail outputs?
good CMRR / PSRR?
If you don't know the answer try the ubiquitous LM358
BTW the circuit I gave is not an inverting amplifier, its a current-to-voltage
converter circuit.
No, do not use a comparator in place of an Op Amp.
That is a perfectly valid PIN photodiode amplifier circuit. See page 9:
http://ecee.colorado.edu/~ecen4827/hw/hw1/PhotodiodeAmplifers.pdf
No, do not use a comparator in place of an Op Amp.
I believe OP wants to use 5 volts only.
A comparator is perfectly valid if s/he wants 0-5V
Can use the LM3900 norton op amp if they want to amplify. . .
See example image:
No, a comparator is not a linear Op Amp.
You can use an Op Amp as a comparator. It won't work quite as well, as an Op Amp is not optimized for situations where the output is saturated.
But a comparator in place of an Op Amp is a terrible idea.
A great book on Op Amps and comparators:
Latest edition in print:
An LM3900 Norton Op Amp is -not- a drop-in replacement for a regular Op Amp.
The circuit you gave will just trigger on or off, no linear measurement.
The OP needs to tell us what he is trying to do.
I am really not impressed with OPs cross posting!
Sorry guys for "cross posting" my time zone is bit different, so it actually makes it a bit hard to get a hold of anyone. Wont happen again
What im trying to do, is create a light measurement system. I.e. For higher intensities of light (im talking very bright - id like to test fibre optics) id expect to have a voltage read out of say close 1023. When its dark id expect it to be at 0. Now, the board only allows me to go from 0 to 5 V so that kind of limits my range. It would be nice to have 2 rails so like from -5 to +5.
Essentially i want to create a circuit using a photodiode with an operational amplifier
I have previously been able to construct a super basic circuit using only the diode and a resistor to control the range and sensitivity but i cant find that sweet spot.
And so id like to amplify my signal and use an inverting amplifier with negative feedback and use the gain to control my range. Im not really sure what kind of gain im after - just what ever is the nicest spread of values.
Its my understanding, that a basic inverting amplifier has a gain of:
Vout/Vin = - R2/R1.
Essentially I need help designing a circuit with the right type of op amp because i have limited experience.
Again apologies for cross posting.
Have a read of these links
http://www.electronics-tutorials.ws/opamp/opamp_2.html
It would be nice to have 2 rails so like from -5 to +5.
The arduino can only handle 0 to 5V on the analogue input pins ( or any other pin for that matter )
Thanks, I've already viewed those. I have tried to do a few circuits using LM324N - more specifically this one.
page 29 of the document on the left hand side - photodiode with amplifier.
Nothing seems to happen. I'm not sure whether the values I'm getting are just too small or whats even happening
trying to get the right image sorry if that doesnt work
if it doesnt visits
Nothing seems to happen.
So post a picture ( not more than 1000 pixels wide ) of your wiring.
