It has the photodiode and amplifier built together on the same chip. The following chart is my data from a tungsten light source ran through my monochromator. I took reading in 10nm increments from 400-800nm wavelengths of light.
Is it possible for me to increase the dynamic range of my setup somehow so that I can read more of the spectrum at a time?
This chart shows runs from (2) different power levels on my lamp. (The lamp does have an IR filter that explains the roll off on the red side but shouldn't affect the violets) The top curve is definitely clipped, the bottom curve does not clip but gives me less signal at the two extremes: violets and reds.
@jremington I appreciate the reply. Unfortunately when I built the sensor I didn't add a wire for terminal #2 on the amplifier so without rebuilding the sensor I can add more resistance between 4 & 5 to increase the gain, that is easy enough to do. I will try that next and see what happens.
I am struggling to visualize how changing the gain will affect the overall response curve, I guess in my mind increasing the gain would just shift the response curve straight down and I would not gain anything on either end of the spectrum.
But I am about to find out. Appreciate the help and I will post my results.
My bad, yes the curve shifts up with more gain. I forgot to add the part where I decrease the lighting power along with the increase in gain to to keep from clipping.
On my monochromator it comes with interchangeable metal slits with different widths. The smaller the slit the more resolution but less light throughput. I am using the middles size slits now. The smallest slits give about 1 nm precision but very dim light.
I have the TSL2591 I use for some other things but the response seemed very limited towards the ultraviolet side of things. It is very easy to use though.
If you want to make a spec, consider using a photodiode array, like the TCD1304.
The TCD1304 data sheet does not reveal the response to light with wavelengths shorter than 400 nm, but it seems to be pretty good. OceanInsight (formerly Ocean Optics) used these sensors in older models of their professional grade, solid state spectophotometers.
To get the full 3648 element spectrum, you need a reasonably fast MCU. It works well with the Teensy 3.2 from PCJR.
That is actually pretty cool, thanks for the link. My end goal with this project is something very similar to a fully functional spectrometer; one that reads the entire spectrum at one whack using diffraction grating and linear CCD. For now I am just taking my first baby steps with measuring light.
Looks like a good instrument. It would certainly be useful for illumination at a single or narrow band of wavelengths, if you were interested in collecting, say, fluorescence emission or Raman spectra.
Which A/D converter are you using.
An ADS1115 has a 15-bit resolution, and can be switched to 4.096volt Aref, which can both fix your top and bottom clipping.
Leo..
If i could read I would have seen @Wawa recommended an ADS1115. I will for sure check it out. I am in the very early stages of this project and was trying to get something up and running to play with.
I have ADS1115 ordered and should be here end of this week. In the meantime I am educating myself more on the fundamentals of this photodiode and transimpedance amplifier.
I have to admit my knowledge of electronics is very limited and I am struggling to understand all the concepts involved. So a couple of questions to get me started.
I read where stray capacitance can have a large impact on the performance. Right now I am using a breadboard which is probably the worst thing to use. I have some of those green prototyping boards with the copper pads at each of the holes. Will this be adequate or should I come up with some without the copper pads?
Any other suggestions you have that will help me out would be appreciated.
I wouldn't worry about it. With too little capacitance, the amplifier will oscillate, but there seems little chance of that given the internal 8 pF feedback.
Perfect! You have been a big help to me... I will have questions latter on and I hope you can continue to help me as I study. It has been very fascinating so far.
