If you have questions or comments about the CN0312, please use this discussion board.
Nice article, I'm very interested in citing it but is not so obvious to me - please suggest a citation for this one. Also, in spite of it's outstanding quality, it lacks some useful references; please suggest some other related works. Thank you!
The last reference in the 'Learn More' section covers a some of the principles discussed in the article:
Skoog, Douglas A., F. James Holler, and Stanley R. Crouch. “An Introduction to Spectrometric Methods.” Instrumental Analysis.USA: Brooks/Cole, Cengage Learning, 2006.
In addition, you may want to look at a book called "Photodetection and Measurement: Maximizing Performance in Optical Systems" by Mark Johnson.
I have a question specifically on the gain selection of the transimpedance amplifier. You guys use two ADG633 switches instead of one, to correct the ~50ohm gain error introduced when a single switch is incorporated into the feedback path of the amplifier. What I don't understand, is how does the second ADG633 actually correct the error?
If you look at the circuit, the desired output is the voltage across the feedback resistor (Idiode * Rf). This is the output voltage is no switches are in the feedback path. If you were to use a switch in the feedback path to select the gain, the output would now be Idiode * (Rf + Ron), where Ron is the switch on resistance.
The second switch allows us to look at the voltage not at the output of the op amp, but right at the feedback resistor. This voltage is Idiode*Rf. So, the inner switch closes the loop with the desired gain, and the 'outer' switch picks off what voltage to measure. The caveat is that the output of the circuit is not the low output impedance you would expect from an op amp output. Rather, it is dominated by the outer switch's on resistance, so whatever stage follows this circuit needs to be high impedance.
But, what about the software component and digital hardware considerations, how does the flowchart look like and what are the minimum processor specs, in order for the software to do the job?
I'm new to the reference circuits and have some questions about the CN0312 Colorimeter that would be great to have answered.
- What are the exact wavelengths of the three LEDs of the board?
- Can these LEDs be changed?
- What is the max frequency of the turning of the beam splitter and can it be programmed?
- What are the features of the CN0312 application software? The the absorption of R,G & B can be seen using the software, but can you adjust the gain of the amplifiers using the software, for example? (see the video in the link: http://videos.analog.com/video/2329050556001/Dual-Channel-Colorimiter-with-Programmable-Gain-Amplifiers/ at 01:20)
- How can the CN0312 be programmed? Using C or FPGA and what software/drivers are needed?
- How is the database of known pH-levels programmed?
Please see below:
As you probably know, when you deal with LEDs, nothing is 'exact', as the wavelength will vary slightly with temperature of the LED die. The nominal wavelength of the each LED, along with the manufacturer's part number is:
Green: 527nm -- CREE PN: C503B-GCN-CY0C0791
Red: 624nm -- CREE PN: C503B-RCS-CW0Z0AA
Blue: 470nm -- CREE PN: C503B-BCN-CV0Z0461
The LEDs are soldered on a PCB. If you wanted to change them you would have to de-solder the parts, clean up the holes, and solder the new LEDs on the board.
I am not sure I understand this question - the beam splitter is a fixed piece of glass. The LEDs are on-off modulated, and the frequency has been tested up to 10kHz. The application software does have the option to change the modulation frequency, and you can set it to frequencies much higher than 10kHz, but again, that has not been tested. As you go up in frequency, at some point the LED turn-on and turn-off transients will become a significant part of the pulse, and it will no longer look like a square wave.
The transimpedance amplifier has two discrete gain settings, and you can select either one (independently for each of the two channels) with the application software.
The CN0312 is meant to be a reference design board only, and we do not support third party programming. Having said that, you CAN program with external hardware rather easily:The CN0312 main board communicates with the application software using the SDP board. However, the interface to the CN0312 main board is just an SPI port and some digital I/O pins to set the gains and modulate the LEDs. You can see this in the full schematic provided as part of the design package:
The SPI port is used to communicate with the AD7798 ADC, and we do provide a No-OS Driver for it. You can download the driver here:
Like any other instrument that performs matching, you must start with some known samples. You would measure each reference sample with the CN0312 board and then add it to the database (which is nothing more than an empty directory where you store one file corresponding to each measured solution). Once you have added all of the solutions you wish to have as reference, you can start matching against the database.
I have gone through your evaluation board Dual-Channel Colorimeter with Programmable Gain Transimpedance Amplifiers and Synchrontious Detectors.And I wish to know more about this device.Can i use this devices for the application of liquid food quality check?what will be the parameters that can I measure from this devices?Whether it is possible to make this in to a liquid food quality check portable handheld devices?
This application is designed to measure the amount of light that passes through a liquid sample. It would be interesting to try to test this with liquid food, and I don't see a reason why it wouldn't function from a theoretical standpoint.
I think the biggest thing to take into consideration is "how think is the liquid food"? If the liquid food doesn't allow light to pass through, than it might be hard to get meaningful measurements. The main parameter that is measured in this system absorption of color through the samples.
Thank you for the response..I have one doubt..Which software is you are using for the spectrum analysis?
The software that is used is an ADI specific software, created using a program from National Instruments called Labview. Labview allows you to make custom applications, and for this particular design we wanted to look at the absorption measurements of the light and translate that into an amplitude across the 3 primary colors (red,blue,green)
That software can be downloaded from our FTP website here (ftp://ftp.analog.com/pub/cftl/CN0312/ )
Will you please provide me the program in the Labview??.....Really urgent for me...plz help me
The software can be downloaded from the FTP site here.
Unzip the file and run the executable.
Below are my queries about Dual-Channel Colorimeter with Programmable Gain Transimpedance Amplifiers and Synchrontious Detectors,
1.From this evaluation board concentration measurement of different samples are getting..How can I change that concentration into liquid food purity check?or how can I evaluate purity of a liquid food from this concentration?
2.Can I check quality of the liquid food?On what basis I can understood that this liquid is not pure..or pesticides /pathogens are contained in this liquid food?
plz help me sir
I don't think that we'll be able to supply you with an algorithm that changes the concentration into a purity check. This is something that you will need to develop and understand how the concentration of absorption equates into a tolerable range of the product you are trying to measure and test.
I also don't think (but don't know for sure) the amount of light absorbed has much (if any) correlation to whether or not pathogens or pesticides can be detected using spectroscopy. Might want to do some research on how those tests are typically done, and see if there is any over lap with this type of sensing. My gut tells me that you will need a secondary test for that, but again I'm not a subject matter expert in this area.
We implemented an optical detector system based on this (CN0312) reference design. It works very well, but we are planing to redesign our device for multiple (at least 16 ) diode input.
I have seen new Circuit from the Lab design with digital synchronous filter (CN0363) with less analog frontend parts, therefore using this design for multiple channel instrument would be obvious.
Please help to compare performance of two implementation.
Glad to hear you had a great experience using the CN0312 optical front-end in your first generation design.
You should see better noise and accuracy performance using the CN0363. The amplifiers are better performing and there are less components in the signal chain to contribute additional noise. The ADC is also faster which allows for some oversampling in the digital domain, and gives you improved performance.
It would be a great choice if your upgrading to a multichannel design.
Thank you for clarification. I will open another discussion for CN0363, as I cant find Zedboard implementation details (link doesn't works).
I found the link:
EVAL-CN0363-PMDZ HDL Reference Design [Analog Devices Wiki]
Sir what do you mean by optical detector?For what purpose it is used for?
The reason I'm calling it optical detector is, that we are using reference design for optical property (transmittance) measurement not for color detection.
Anyone can help me to develop an algorithm for checking purity of liquids
But we don't provide algorithm development. I'd recommend contacting a local software contractor, and preferably one that understands some of the things your trying to do.
Thank you sir
Is there any other application for this evaluation board instead of measuring the amount of light that passes through a liquid sample? For what purpose you are using this evaluation board actually?
This reference design board is used to measure the amount of light that passes through a "sample". In colorimeter/spectroscopy applications that sample is typically liquid. I'm sure you could try to test slightly denser samples, but there has to be some light that will come through or else the sensors won't work. The circuit is designed to take extremely small currents (from photodiodes) and signal condition/digitize them.
Hi Brandon Bushey,
Will you please explain the exact use of below two boards?.What is the need of Eval Control Board?
Well the EVAL-CN0312-SDPZ is the application board, and that does all the work of capturing the light samples and controlling the LEDs, its the hardware for the colorimeter.
The EVAL-SDP-CB1Z is a controller board that will allow you to plug EVAL-CN0312-SDPZ into the computer and run the customized Labview evaluation software for the colorimeter application.
When plugged together, the controller board simply acts as an interface to Windows. For more information on the controller board, please visit this page. (http://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/SDP-B.html#eb-overview ) This controller board is use for a variety of boards at Analog Devices.
what are the product specifications??......
What is the need for AD8615 connected just before ADG733 ..Actually AD8615 is an amplifer right?...Is this the same function here too???
So the AD8615 before the ADG733, is used as a precision driver amplifier. The driving capability of the ADG633 wouldn't be enough to directly drive the ADG733.
thank you Brandon
If I am going to buy this evaluation board , Beam splitter,Cuvettes,LED's,and photodiode will be there along with this kit right??
What is the exact diameter and reflection/transmission (R/T) ratio of that beam splitter?
Can I use a different beam splitter having different R/T ratio?
The kit itself includes the beam splitter, photodiodes, LEDs, and 2 cuvettes. So when you get the kit, you should be ready to try it out.
The beam splitter we used is a 50/50 ratio, but you can do other ratios if you want, you'll just have to adjust your calculations for that. The beam splitter part number used can be found in the BOM. http://www.analog.com/media/en/reference-design-documentation/design-integration-files/CN0312-DesignSupport.zip
Hope this is helpful.
thank you Brandon...
Can you suggest any other beam splitter and photodiode that suits for this evaluation board
Any beam splitter or photodiode that would fit the footprint on the board should work. I would recommend looking at the part numbers called out in the BOM, and then check out those manufacturers websites to see what other similar product exist. This will give you a starting point of the electrical and mechanical specs that would need to be adhered to.
Can you please provide the specification of cuvettes used here??
Sorry for the delayed response.
The cuvettes used with this kit come from a company called Azzota. The part number is "A912" and there are two shipped per kit.
Thank you Brandon.I have one more question.Can I use SDP-S controller board instead of SDP B controller board?
What is the exact dimension of this evaluation board?
Is there any warranty for this evaluation kit?
what is the purpose of ADR4525 in the evaluation circuit?Its realy urgent sir, so that a fast reply is highly appreciated..
I had to do some digging into the source code, but I was able to determine that the SDP-S cannot be used. You will need to use the SDP-B board
The dimensions of the board are about 5 inches by 7 inches (13 cm by 18 cm).
The ADR4525 creates a very stable voltage reference, that is used by the sigma delta converter to convert the analog signals into digital signals, as well as providing a precise voltage level to turn on and off the the LEDs.
I have started my project work based on this dual channel colorimeter.It is just a beginning of my work.and in that I have used LED DRIVER CIRCUIT,LEDs,2 CUVETTES,BEAM SPLITTER,AND POWER METER AS DETECTOR..And from this I am getting only the power readings.How can I convert this power readings into concentration???pls help me
I'm not exactly sure what you mean by "power meter", but provided with the evaluation kit is some application software designed to tell you how much of the light spectrum was absorbed through the three primary colors. This is used basically as maximum voltage measurement of the sample, which is converted by the analog to digital converter.
I'm not sure I can help much with your concentration question, this seems like something you should research to determine what kind of math needs to be done to the output. Just remember that the A/D converter is converting the voltage which is proportional to the amount of light that passes through the sample.
Its really happy to say that, I bought the evaluation board.And liquid food adulteration experiments are going well..I have one doubt about the GUI..How can I save my readings into the sample library??I could not do till now..So simply exporting readings into excel pages.....pls help me
Hope you got my message.If you are free, please do reply sir
Glad to hear that the CN0312 is working well for your experiments.
I've attached a word document(from a colleague) which outlines how to use the "sample library" and "matching" functions on the GUI. Please read through this and replicate these steps.
Thank you Brandon for your help..I will message you after doing my experiments about this sample library.
What is the product specification of this CN0312 dual channel colorimeter?
I mean the input power,output power,etc...pls help me
I do understand your question, what specifically do you mean "input power" or "output power"?
I want to make product specification...For that I wish to know about the evaluation board spec..
So we don't have a spec that has been tested for the CN0312 board. All the details that we have regarding the CN0312 will be found on the web page. http://www.analog.com/en/design-center/reference-designs/hardware-reference-design/circuits-from-the-lab/CN0312.html#rd-…
I find below description in CN0312
"Adding an optical feedback loop to control the amplitude, the LEDs greatly reduce light variations with temperature and may even make it possible to make accurate single-channel measurements."
Can you help to explain what's the optical feedback loop, sorry for trouble you.
To implement optical feedback you would need to add additional photodiodes and amplifiers to monitor the light level out of each LED. You would also need to drive the LEDs with D/A converters so you can adjust the LED drive current. You would use the digitized I/V output to set the D/A converter level so that you maintain a constant LED light intensity.
Retrieving data ...