I am currently working on a sensor chip which uses conducting polymer as the sensing component. I can see it working when it is connected to a source measurement unit (SMU) in my laboratory. I am now trying to power the chip with an arduino microcontroller. The problem is I only see a very small signal change when it is subjected to an analyte. The baseline is at around 700 from the analogRead and the signal is just 715 and the response is like a step function. I do not have much knowledge about electronics since I am trained as a polymer chemist. I connected my chemiresistive sensor like connecting the photodiode experiment example in the picture below.
Someone suggested me to use operational amplifier. I bought some Op Amp (LM318, IC741, LM301), but I have no idea how to connect them. I was also told that these Op Amps require an external power to make them work. I also wonder if Arduino microcontroller alone and power any of these Op Amps without using an external power supply?
Better option for non-EE person would be an external ADC, 16 or 24 bits, something like ads1118, ads1116 or ads1232. There are pre-build modules available on the market.
FantomT:
Better option for non-EE person would be an external ADC, 16 or 24 bits, something like ads1118, ads1116 or ads1232. There are pre-build modules available on the market.
Thanks for the suggestion. Is there any particular difference for the external ADC ads1118, ads1116 and ads1232 you mentioned? Which one would you suggest to buy? Can I also connect a variable resistor to "adjust" the baseline of my sensor with these external ADC?
Personally, I prefer ads1232. It has internal amplifier, so sensitivity could reach outstanding nano-volts scale.
For others, I would suggest google search ADS12XX + arduino + tutorial, with good explanation and many pictures, possible video. Choose the one you understand and feel easy to accomplish.
FantomT:
Personally, I prefer ads1232. It has internal amplifier, so sensitivity could reach outstanding nano-volts scale.
For others, I would suggest google search ADS12XX + arduino + tutorial, with good explanation and many pictures, possible video. Choose the one you understand and feel easy to accomplish.
Thank you so much for the advice
I saw the spec of ads1232 , saying that the Operating voltage is 2.7-5VDC . Does that mean I can even power it with the 5V power from my arduino without using any external battery? Thanks!
The OP doesn't seem to understand they haven't got any prospect of it working
at all until we sort out the sensing circuit and for that we need to know more
about the sensor itself.
Hi, This is how I connected my sensor to arduino at first. We measured the signal with an SMU in lab, and the signal is around 20-90 microamperes (and no problem to give a smooth curve since the SMU has a higher resolution). In Arduino the Current vs time graph looks like the picture shown when we introduce the analyte. I want to make the sensor a portable prototype so that I can bring it to somewhere else to sense different things.
The sensor is a chemiresistive material I synthesized in lab and coated on 2 electrodes. It is not a transistor based sensor or any commercially available sensors we can find in the market.
I dont really know how to work with Op Amps. But these are the Op Amps I have LM318, IC741, LM301. I also bought an Analog to Digital Converter module ADS 1232 which was suggested by FantomT, but still I do not know how to connect the circuits! Any tutorial would be greatly appreciated!.
Does the mysterious SMU measure change in current as you apply analyte? If so, an op amp could be used as a current to voltage converter (called a transimpedance amplifier).
The graph and diagram you posted does not appear to agree with the annotation. If I am interpreting the graph correctly, a change in ADC reading of 8 (from 692 to 700) implies a change in current of 4 microAmperes across a 10K resistor, or a change of 40 uA across a 1K resistor -- it is impossible to tell which from an unlabeled Fritzing idiot diagram.
jremington:
What is an SMU? What do you mean by "signal"?
Does the mysterious SMU measure change in current as you apply analyte? If so, an op amp could be used as a current to voltage converter (called a transimpedance amplifier).
The graph and diagram you posted does not appear to agree with the annotation. If I am interpreting the graph correctly, a change in ADC reading of 8 (from 692 to 700) implies a change in current of 4 microAmperes across a 10K resistor, or a change of 40 uA across a 1K resistor -- it is impossible to tell which from an unlabeled Fritzing idiot diagram.
Hi, SMU is a source measurement unit used in our laboratory. The SMU measures the change in current when we apply the analyte. Below is how it looks like when it is tested in my lab SMU.
What I am trying to do is to get the same graph as the one in SMU (with a smoother curve or higher resolution) in arduino, instead of having a graph like this.The connection in the arduino is a change of 40 uA across a 1K resistor.
From the info you have provided, the sensor acts roughly as a 480 Ohm resistor in the absence of analyte, decreasing to about 462 Ohms in the presence of analyte.
Such a change could be monitored by Arduino using a Wheatstone resistance bridge and associated amplifier, similar to how strain gauges or load cells are read out.
Google "arduino strain gauge amplifier" for lots of tutorials on that topic. The HX711 amplifier/ADC and three 470 Ohm resistors might work.
jremington:
From the info you have provided, the sensor acts roughly as a 480 Ohm resistor in the absence of analyte, decreasing to about 462 Ohms in the presence of analyte.
Such a change could be monitored by Arduino using a Wheatstone resistance bridge and associated amplifier, similar to how strain gauges or load cells are read out.
Google "arduino strain gauge amplifier" for lots of tutorials on that topic. The HX711 amplifier/ADC and three 470 Ohm resistors might work.
But what does the Arduino bring to the project?
Thanks for the reply.
Is it possible to use the ADS1232 to do the similar thing?
Hi,
I tried to use an LM741 Op Amp to do the signal amplification, but I sort of failed to get an amplified signal (same low-resolution signal). In fact, I am not sure how the battery supply shall be connected. I just used one 9V battery and connected the + to Pin7 and - to Pin4 of the LM741 (which I laterly know it is a wrong connection).
I then googled some Op Amp connection in reality which the datasheet dont actually show and found something like this:
If I use the above image as a reference, Do I really need two 9V batteries to make +9 and -9 Volts? and how to I connect the ground? just to the ground pin on the arduino microcontroller? will it damage my microcontroller? Can someone explain a little bit more about this to a non-ECE person?
That type is ancient - get a halfway modern one to begin with!
Most modern OpAmps work fine on 5V single supply. Safer than 9V also as you're sure the output can't kill the Arduino.
