hi , i made photodiode transimpedance op amp circuit . with maximum illuminance i am getting - 4.3v as pre amp output but i want 4.8v output for maximum illuminance so added inverting amp for getting 4.8v but i am getting 3.7v output from inverting amplifier with maximum illuminance . i try adjust the input variable resistance 15k but i could not get 4.8v output . op amp rail voltage is ( +5v , 0, -5v ) .
Which opamp type do you use?
using lm358 and you can suggest low voltage range (+5v 0 -5v) opamp.
do you think lm4558 will be suitable ?
This is not a rail-to-rail opamp. Hence, if you feed it +/-5V, its output can never swing to +5V; it'll go to about 3.5V max according to its datasheet. So your observation of 3.7V out is about right. I don't know why your first stage manages to swing all the way down to -4.3V; I wouldn't have expected it to go below something like -4V.
No. It's not rail to rail either. Furthermore, it has a fairly high input offset current which is far from ideal in your use case.
Try something like AD8605/8606.
1: you need to use a suitable rail-rail op amp as described in the tutorial. Depending on your application you will need to choose a type with a suitable bandwidth.
2: no rail-rail op amp can ever achieve true rail-rail output while driving current. So it depends on your load and also on the fedback resistor.
3: why does your max output HAVE to be 5V? If you are measuring it you can scale your measurement to suit.
hope so your shortlisted op amp list will be much more useful . i will try from that list.
because 0v to 4.9v variation voltage will give broad range of a/d conversion data i can get . measurement sequence much more precise.
All you need is for the range of your output to match theinput range of the ADC
Depending on which arduino you use the internal reference will be 1.1V or 2.5V
True. Or, if e.g. the popular ADS1115 is used, the range is selectable from 256mV all the way up to 4096mV.
Moreover, maximizing the ADC's range isn't necessarily the most important target. Determine how much resolution the application needs and then optimize for it. Maybe you need only 9 bits out of an A328P's 10 bit range, or 15 bits out of the ADC1115's 16 bit range. That immediately allows you to 'only' swing voltages up to half the ADC's full range voltage while still maintaining required resolution...
i agree both of you ads1115 is to get good resolution .
i am not too concern about 5v max output . incase of less light intensity i need to little boost the pre amp signal to max .
example with less light pre amp out put will be very less then scale will be very small even with 16 bit range . i need the digital gain control by Post Amp & offset control . TL074 currently available here i will try with this or i will try with AD8605/8606.
Yeah, that's kind of the point with a transimpedance amplifier, isn't it? Lots of light = big signal, less light = small signal. I'm not sure I understand your 'problem'.
Anyway, since you've told nothing about your application, it's pretty much impossible to say anything useful. Your basic circuit works, and the output can swing close to V+ IF you use a rail-to-rail opamp, or considerably less if you don't.
the project about measuring light intensity based on the colour tape transmission . we don't want colour reflection or colour sensor .
we want to measure the colour intensity .
So will you be illuminating the tape sequentially with various color LEDs and measuring transmission each time? Or will the setup be an RGB photodiode with 3 elements and a broad spectrum light source? Have you measured the light intensity range, put that next to the photodiode datasheet and figured out the typical current range you can expect from the sensor?
In short: have you done the theoretical work to get a ballpark estimate of how much gain you need from the analog frontend?
That's the problem - if you stop wanting 4.8V and start wanting 3.6V all is solved.
no LED . small size incandescent lamp. currently working with blue color .
Theoretical part :
Calculation based on Amount of transmission of light received in senor with tabe and without tabe( base zero value ) .
100% Transmission Value is zero color .
Based on the percentage of light intensity is inversely propositional to color concentration .
Amplifier Gain Part:
i couldn't conclude the Gain part . it's just development stage .
As of now i observed Dark Blue Tape and Light Blue tape giving different voltage . incase of yellow color i need check Measurement Linearity of Amplifier Gain response . i am working with this part now .
your suggestion is most welcome .
Poor choice. Unless there's a compelling reason to stick with this, I'd strongly suggest to not use 19th century technology for this critical part.
Yeah, I get that...
The question is: how much light exactly is 100% transmission? Of course it's never 100%, but I get what you mean - a clear tape/film is defined by you as 100% and any coloration would result in a transmission of less than 100% in whatever color channel you measure.
OK, so you're working on blue now, but you have an incandescent lamp, so a broad spectrum light source (with very poor performance in blue, but let's put that aside for now). How do you 'single out' the blue light? A filter in front of the lamp, or the sensor?
You mentioned that you don't want to use an RGB color sensor. Could you explain why? I'm asking because there's about a 99.8% chance that this will make your life much easier. You're most likely reinventing the wheel, and doing it poorly if you compare your efforts with what e.g. an AS73211 has to offer.
just for high intensity i used incandescent lamp and wide range of color source & Violet (close to 405nm) - Not UV- above the UV - below violet or close violet .
RGB sensor doesn't have the little & medium violet response if know some RGB with UV response color sensor it will be ok .
standard filter will be used before the light source .
Just a quick example of a possible solution...
Odd. Incaddenscent is just about the most inefficient solution, i.e. LOW intensity per Watt input.
For which incandescent is just about useless!
Sounds like you have some groundwork left to do.
I think you asked for greater light sensitivity? You can get some by increasing the op amp gain. For example change the 1M resistor to 10M, or introduce another op amp gain stage after it. With such a high value feedback resistor, though, you will need to use an op amp with an extremely high input impedance like a JFET or CMOS op amp.
This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.