Photodiodes not sensitiv enough / How to amplify?

Hello,

I'm currently working on a camera shutter tester where i measure the time where photodiodes get hit by light.

The circuit is really simple right now.
The diode is connected to a digital pin and GND, the same digital pin is connected to 5v with a 100k resistor.
I'm working with digitalread as analogread is not fast enough
for my application.
The circuit keeps the digital pin high and the diode pulls the digital pin low when hit by light.
I can change the sensitivity with using a higher resistor like 3M but this way the measured time is not accurate any more and the time is displayed much longer than with the 100k resistor.
With the 100k resistor the measured times seems to be accurate but the the sensitivty is quiet low and i need really a lot of light to get the diodes triggered.
Is there any easy way to get the diodes really sensitiv with keeping the rise and fall times accurate so they stay precise ?
reading the diodes analog i can see that diodes only are pretty sensitiv, so my circuit to get a digital signal seems to be the problem.
does someone know a simple circuit to get a precise digital signal with a high sensitiv diode ?
I was thinking about getting a KY-037 microphone module and swapping the microphone with one of my diodes would this be a way ?
thanks for you replies upfront
Benjamin

Photodiodes provide low current only, what makes loading the input capacitor slow. Add a quick amplifier that can provide more current.

Thanks for your reply ! Do you know an amplifier like that ?

It's a complicated subject, there are a few really detailed monographs and application notes around from the manufacturers, as well as academic sources. I suggest you start looking there, as the detail you need to really apply the right techniques would turn into a long novel here.

It can be interesting! For example a diode capacitance decreases with reverse bias, so a reverse bias increases bandwidth. See the bias connection "+Vb" below. :slight_smile: Edit, OOps it's been edited, oh well..

Search for "photodiode transimpedance amplifier". One simple example below.

From Optimizing Precision Photodiode Sensor Circuit Design | Analog Devices

Here is the image that @aarg referred to. It is an alternative circuit with reverse bias, which speeds up the response. I replaced it because of the broken connection on the right.

I suggest trying even lower resistances than 100k! There's capacitance to overwin.
Please post the code, in cidew tags, </>.
Setup a well controlled situation for repetable tests of that resistor.

Just provided as info. A PMT, Photo Multiplier Tube could be used to amplify the light and turn the light into an electrical signal.

Solid state photomultiplier devices are, also available.

The circuits that maximize sensitivity, decrease bandwidth, and vice versa. If your circuit requires an op amp, make sure it's a fast one. No LM741 here please. :slight_smile: A JFET input op amp would be a good choice to minimize input DC offset.

Your idea of re-purposing a microphone preamp is interesting, but is a non-starter.

thanks !
Are there any ready modules or which exactly parts would be needed ?
So how would this circuit would look connected with an arduino nano ?
So this circuit would turn V out high when lights hit the diode and other wise would keep it low ?

Sorry for all the questions but i dont know so much about circuit diagrams.

Yes i found some academic sources for that field but to be honest way to complicated for me.
Im actually a camera repairs man and know better about mechanics then electronics, its just that im really in need for a precise tester so thats why im actually started with arduino :grinning:

Even with this 100k resistor its already not sensitiv enough so using a lower one will not solve my problem as it will be even less sensitiv.
Its nothing code related, my code runs fine.
Its just about switching a digital pin high or low and getting a photodiode doing this precisely with high sensitivity where the help is needed

If you intend to pursue this hobby, it is a good idea to learn to read schematic diagrams. Decent tutorial here: How to Read a Schematic - learn.sparkfun.com

The first circuit provides a positive Vout that can be connected to an Arduino input, but it is incomplete. You need a fast op amp and a few additional components. The second circuit cannot be directly connected to Arduino, as the output is a negative voltage.

its just that im really in need for a precise tester so thats why im actually started with arduino

Unless you are willing to undertake a considerable learning journey, it would be a better idea to buy one.

Look for "photodiode module".

I'm always willing to learn, and especially in this case buying one is not an option as a tester is hard to get by also as im a student and they are mostly far out my capital.
There is manufacturer in Japan but a machine would be 12000€ or more.
I'm looking for used tester since 4 Years but couldnt find one.
a precision from +-1 microsecond would be perfect so it doesnt need to be any more precise than that if its a bit less i still could live with it

Are you sure the problem is sensitivity and not really the response time of the circuit?
Paul

You could ask the forum moderator to move your post to the Jobs and Paid Collaborations forum section. Someone might be interested enough to design the photodiode amplifier for free, although there are plenty of good designs on the web.

Right. First thing I would do, put an oscilloscope on it.
Also, can you not simply increase the shutter illumination?

Allready tried one of these lm393 ones, didnt got enough sensitivity.
I soldered my good diode on which i pulled out of the lightmeter system of Olympus Cameras.
Thats the diodes im using, they are called silicon blue cell
thats the information given from Olympus:

  1. Very quick response speed (10^-6 sec) enables real time and unremitting light measurement.
    2.Dark current is weak and accuracy on the low luminance level is high
    3.Electromotive current caused by incident light changes linearly
    4.Bluefilter applied lowers the infrared-ray below 15%

There's some circuit talk here now, it's too vague without a schematic. Please post one. Also links to the hardware.

Typical photo industry "plumping up". You have my sympathy on that one.