Using a Capacitive Proximity Sensor as an Analog Distance Sensor?

[ddowns46]

I am working on an Arduino PID control project and I want to use a capacitive sensor for detecting the distance between a target and a steel plate. I need the output signal from the sensor to be analog so that I can use it to measure the distance. For some reason I am having difficulty finding a readily available low cost capacitive sensor that has an analog output.

I see there are lots of cheap capacitive proximity sensors but they appear to just be NO/NC with no way to get an analog signal. Or can these be modified to output an analog signal?? If so how?

If there are cheap analog sensors that will do the same thing I'd love a recommendation! Looking to sense around 0 to 0.75" distances.

Link below for the proximity sensors I've been looking at.

https://www.amazon.com/Taiss-1-10mm-Capacitance-Proximity-Sensor/dp/B07PX95MPC

 

[BrianE22]

Magnetics are frequently used with steel. They can give you a linear output. Try Allegro. On Digikey search for Hall Effect.

 

[3DDave]

They don't directly sense distance. They sense a change in capacitance. Some microcontrollers have a capacitance sensing function, usually touch sensors. The switch sensors are doing the hard work of calibration to a known capacitance condition and then signally when the capacitance changes by some amount.

https://www.youtube.com/watch?v=LixzM2YghS8

Here's a writeup that might be useful:

https://www.ti.com/lit/an/snoa927a/snoa927a.pdf?ts=1675048173744

Here's an example application:

https://www.tindie.com/products/protocentral/fdc1004-capacitance-sensor-breakout-board/

There may be others, but I saw mostly items were development boards in the several hundred of dollar range.

 

[ddowns46]

How would one use a sensor like the cheap Capacitive proximity sensor and breadboard it so that the output was an analog voltage based on distance? Basically what I would want to do is put a voltage to the sensor and have the output be an analog signal of voltage that is proportional to distance from the target.

 

[tygerdawg]

low cost / cheap / cheap

You may want to clarify what that means. You're probably not going to like the answer.

Generally, inductive better for ferrous, capacitive for nonferrous.

The one critical spec that is missing is resolution / accuracy. Not much else matters until you define your needs.
There are plenty of analog output prox sensors on the industrial market. Low cost / cheap / cheap? Depends on your definition.

A prox that will sense out to 0.75 inch [19 mm] is not too common, but there are a few out there.
You may consider either an ultrasonic sensor with analog output (if you can work with the resolution those provide).
Or one of the analog output laser displacement sensors on the market. The high accuracy units are very costly but smaller ones are more reasonable. But that probably doesn't fit your definition of low cost / cheap /cheap.

TygerDawg
Blue Technik LLC
Manufacturing Engineering Consulting

http://www.bluetechnik.com

 

[IRstuff]

You apparently haven't even attempted to do ANY analysis. Your Arduino is unlikely to be able to give you much accuracy, given the capacitance below.

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[3DDave]

Maybe - this claims a circuit to go to 1pF ->

https://electronoobs.com/eng_arduino_tut10_1.php

though that's a lot of area for a sensor.

TI already makes a sensor for this application and the above breakout board works with a much smaller area. The FDC1004 claims 0.5 fF resolution.

I think the main error here is the belief that there is an analog stage that has a high-level signal amplifier in the switches that can easily be adapted.

 

[IRstuff]

I think the OP is confused about the concept of "analog" since an Arduino is clearly NOT an analog processor

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[3DDave]

The prototypical Arduino processor, the Atmega 328P has a 6 channel, 10bit A/D capability (I think it is one convertor with 6 way switching) so it could do some of it, just not without help from a resistor or two.

It is also clearly not a great way to measure distance.

For the student - when you find it difficult to locate something you think should be cheap and they aren't? There's probably a reason for that. Creating your own sensor might work, but think of the hundreds to thousands of others with at least as much experience who have not made one for sale. The question to ask is, is there some fundamental physics aspect that they have missed? For certain if anyone found value in gutting a capacitive switch some one by now would have made a YouTube video how-to.

Still, worth asking, but a lot more reading might cause a shift to a better solution. Also, including the application limitations (how big a piece of steel? Does the thickness vary? Is it the same piece of steel? Is there more steel near it?) would aid in prompting those alternate solutions.

Best of luck

 

[IRstuff]

On the flip side, laser distance measurement instruments are readily available and inexpensive; the one below has Bluetooth and continuous measurements, but I don't think it's measurement rate is going to be good enough for this type of application. The Leica datasheet implies one measurement every 7.2 seconds

Leica Disto Di


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