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Tutorial: Op-amp circuit for force sensor signal conditioning
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- Опубликовано: 8 дек 2011
- This is a description of a simple opamp circuit that will translate the variable resistance of a Flexi-Force sensor into an analog voltage and maintain linearity across the sensor's measurement range.
www.tekscan.com/flexiforce.html
www.national.com/ds/LM/LM124.pdf
Your feedback and topic suggestions for future tutorials are welcome.
Thanks very much. I think that your approach with a regular problem (measuring), designing the curcuit, doing the math, and the showing it working is SO EXTREMLY AWSOME.
This is exactly what I need. I can see a lot of YT videos regarding theory, but from my point of view its difficult to get from knowing behavior of components to a real application.
Please make more videos like this. And from my perspective you may add quite more theory. I think the term "Applied Science" really is the fundamental challenge in this world, and apparently you are one of the very good sources. Thanks a lot :-)
I would be so thankful for a in depth video on H-Bridges, the basics but also with more power consumption by the motors (for diy robots e.g.) Thanks in advance.
man another ripper video. we need to make a statue of you in the townsquare looking to the future holding an opamp
I love watching your videos because your projects are always different and you're so good at explaining things! You should come teach at Purdue!!!
Great video! Probably one of the few in RUclips that explains designing a circuit quite well
The only thing I didn't catch was your noise considerations. The piezo can have large impedances, and the op-amp current noise will generate a voltage noise source with it. Perhaps for your purposes it doesn't matter, but in real life design, one is sure to provide a detection limit based on it as well.
Great stuff, as usual. I really enjoy your channel - straightforward, to the point, no BS!
Thank you so much! You taught this old mech eng exactly what I needed to know to get my FSRs working!
Great tutorial and refresher from my EE classes! Thanks!
very well explained... the 324 op-amp is very useful with lots of examples 😎 thanks this would be nice for simple load cells
Nice videos you have!
You could reduce the different number of voltage regulators of your design if you use the internal voltage reference of the atmega. It is 1.1V or 2.5V depending on the exact model and it is usually more accurate than the 5V of an standard linear regulator. Just put an 100nF to ground on the Aref.
With the scope on the highest sensitivity it looks like your speech is picked up by the sensor and can be seen on the screen.
Cool! Analog signal conditioning is one of my favorite topics.
My first thought when i started watching this was that you where going to use an antilog amplifier (a circuit that uses the logarithmic voltage response of a semiconductor) but this is perfect when you just have a variable resistance, same technique is used for tailoring potentiometers, never saw that using an opamp before though.
I'd like to experiment with this my self, maybe you could eliminate the inverter using an antilog amp...
Really liked the video! Very helpful. It does make me wonder what kind of results you'd get by scaling the signal in software.
Great vid & solid explanations! Thanks! 👍
I really enjoy your videos .. love the tutorials .. I would also like to know what you are doing with all of the pressure sensors .. :)
Thanks for the Simple Explanation
So helpful
Good job mr. Thank so much
Keep 'em coming, more like this!
Thank you very much... thats a lots of work
you might try the adhesive/epoxy used in auto glass repair
Nice tutorial for beginners!
What would those sensors will be used for in finished installation? (If you can tell this information, of course)
This is a very interesting tutorial. However in case one wanted a variable resistor to adjust the gain, I guess you could not put the filter in the op-amp loop and put it only at the op-amp output. In this case should a second op-amp be used as a buffer between the first op-amp and the RC filter?
Impressive video, but i still think you're greatest accomplishment is when you make aerogel that stuff is AMAZING should make video of you're larger pieces thanks
Very nice tutorial! What are you using the 10 sensors for?
Awsome..enjoyed it.
Thank you for this video.. is it possible to get a diagram, showing how you connected the four sensors and everything together. am doing a weight scale with four sensors connected in series, and am lost on the connection part... please help
Awesome content!!!!!
I'm interested in what kind of project you would use this. For 10 sensors, I was thinking about a robotic foot/arm maybe?
You live near Jameco! Lucky!
What a great video! Thanks for uploading. Question: At 8:30, you start to talk about low-pass filters because the force applied is "not changing," so how would you construct a filter which forces are changing (sometimes rapidly and in small amounts)? Thanks in advance!
¿Some reason to not use non inverting configuration?, with non inverting configuration you can use a zener as regulator for the sensor.
A current source supplying the sensor in parallel with a resistor would also yield linear output voltage without requiring a negative voltage reference.
Ben,
Why not use a voltage follower at the end of the output to get rid of any impedance or loading issues? Are there any downsides to doing this? (besides the necessity of using another opamp)
Many new op-amps are surface mount. Can I still use the board like yours?
Hi Ben,
I have enjoyed your videos for some time. I am just learning about electronics, and I saw something in this video that I think I could use. I would like to turn on and run a stand-by generator in the event of a power outage only when a well pump is needed (to minimize on site fuel storage requirement). Could I use an op amp in a circuit similar to yours in the video to sense conductance in the power circuit when unenergized. The circuit would be isolated by relay once the generator turned on, and the generator would continue to run as long as the tank level controller called for the pump to operate (perhaps by current transformer). Once the load was satisfied, the generator would operate a few minutes more by time delay to cool down. Could a small microcontroller like a arduino be called into service to do this?
In another video, I saw you experiment with a mouth actuated mouse. A company is now making a similar device for the disabled, but utilizes a metal stud pierced in the tongue.
Great video - very helpful and clearly explained: many thanks.
One question: please can you clarify how you wire the DC-DC SRS0505 to get -5V out.
The video seems to suggest: +5V to +Vin, -Vout to -Vin, and -Vout to the Flexiforce transducer, with no connections to earth.
Is this correct ?
You would connect the -Vin to GND. This will result in +Vout has the same potential as GND and -Vout to be -5V as the difference between +Vout and -Vout is equal to 5V.
This is possible since the DC-DC converter is isolated.
Are you sure that is the cutoff frequency? I thought the RC cutoff was the frequency at which there is 3dB of attenuation.
It is, but that is essentially the break point. The filter attenuation is exponential.
Hi, just a quick question, for generating the -5volts do you connect your 5v power supply to the Vin - and Vin + normally and then connect the Vout+ back to the Vin- and connect the Vout- to the force sensor?
doesn't the 8 volt regulator need at least 1.5 or even 2 volts more than in 8 volts it gives out?
and also could this schematic be adjusted to match the curve of an NTC resistor for precise temperature measurement
Hi. I am new to this so very much enjoyed your video. Thanks. I was wondering if it was possible to avoid the negative supply (and reduce cost/complexity) and instead bias the op amp somehow to keep within a Ground to V-1.5v range?
Yes. There are a few ways to avoid a negative supply with op amps. There are also switching converter ICs that will generate a negative supply from a positive supply with an inductor and a capacitor (known as an inverting charge pump). For low current applications, you could even take a 10V supply, put it through a voltage divider that gives half supply at the divider output, use that 5V as if it were ground, use your supply ground as -5V output, and use the supply 10V as the +5V output. Voltages are not absolute, the only thing that counts is the difference between two voltages across a device. You could connect 50V to the + input, and 45V to the - input, and the circuit "feels" 5V.
You could add another negative feedback with Gain 1 to this circuit to remove negetive one power
very interesting
At 2:04, this is why the conductance is a linear graph (recall Algebra 1 I think):
F = A/R
this is the rough equation of the graph in 2:23. If you know y = a/x from math class, you'll know what I'm talking about.
( By the way, let F = force, A = some weird constant, and R = resistance)
Substitute R = 1/C like the diagram and we get:
F = A/1/C = AC
Which is a linear equation! Hooray!
nice video
I don't think that transducer is only made for static loads. It's frequency response is low anyway.
i like lm358 but ebay suppliers keep sending the lm358m which is tiny and hard to solder. can you look at a circuit for me? im tapping rssi voltage output on a fm receiver. atmega88pa based.
hey, i have brought this sensor, and i just want to know if there is any force on it or not, the value doesn't matter for now. So do i need to build this circuit.
Your circuit is nice but for a simple application one can use a current source and then just make a division like 1000/R with the MCU. The only disadvantage I see on that is the non linear accuracy in sensor's range.
Useful
where i the best place to get a couple rolls
I have a question, could I use a LM358?....I tried to amplify 1.5 V DC (coming from a voltage divider) with a gain of 2 (I'm powering the LM358 from a 9V supply) to see if I get a 3V output....well it didn't work....then I tried it with sinusoidal test signal.....this one worked.I'm guessing LM358 can't amplify DC? it doesn't state in the datasheet that it can be used in DC AMPLIFIER BLOCKS as opposed to LM324.Should I use an IC that clearly states it can amplify DC?
+Marian marian2
Ignore the previous question, I was beeing an idiot and putting +Input voltage on the inverting input and wondered like a moron why the output stayed at 0V
How can be conductunce linear when resistance is varing in non linear manner. Since conductance is inverse of resistance
The resistance does appear to be non-linear, but it is infact linear and proportional to the pressure data series.
What is happening here though is the resistance value is _decreasing_ proportionally with the increasing pressure value.
When this is plotted, the result is an inverse graph which has a hyperbola curve like the one Ben showed.
By inverting the decreasing value data series (y axis here) you are converting it into an increasing value data series which, when re-plotted, results in a linear plot.
If, instead, the resistance of these sensors had _increased_ proportionally with increasing pressure, the resultant graph would obviously be linear and converting the resistance data series to conductance would result in a hyperbolic curve.
Why does 2:23 reminds me of derivatives? Well, Thanks for the video!
usefull
I mean I do think its made for only static loads anyway.
👍
I think you made a mistake, the linearized conversion should be the the log of the inverse of resistance.
use the camera which is very tiny and a microphone in a pen
we know every word need a specific time to write down so it takes the specific amount of ink
know we know that every single handwritten words
every word produced specific movement so we made a graph of that movement by a laser beam which record the movement of a freely suspended pendulum
knows it's like a speakers which give same frequency as original voice
if we use a laser beam which record the movement sound of every particular word at the speed and mass of ink and time of writing then we can easily produced the graph of handwritten words
Best book to learn the electric circuit hobby
google for theelectronicsbook
the curve made him upset
electrical enggineerimg stuff
oh man, lm324s suck