Hello all,
I am working on an idea I had a few weeks ago and need some guidance on how to proceed. I know that this isn't a super complex project, but after doing some research I want to read the linear displacement of a DIY linear variable capacitor that is set up as a transducer reading at most 15cm of linear displacement. This is a retrofit, so I cant change the design constraints of the transducer if there is a better option.
I have a hard time reading forums because I have dyslexia, so I really don't mean to waste your time. I am also very new to DIY electronics, so a simple answer will suffice if it is obvious.
The design is space limited, so I intend to use an Arduino Pico. Here are my questions if you can please answer them or point me in a direction I would be extremely grateful.
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Does the Arduino Pico have the capability to read frequency variations as a means of measuring the capacitance as the electrodes are physically moved such as through the serial plotter program? This is probably an obvious yes, but I just want to make sure. I don't currently have a Pico, so that is why I cant simply verify this on my own.
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Are you aware of any available code to run that is designed for this application? As well as any wiring diagrams, or preferably an available PCB for this exact thing? I have wiring experience but figured I might as well ask since I am already here. I am not skilled enough to miniaturize it to the scale I need so I intend to get a test board printed when I verify the design and code is compatible.
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Would a frequency variation reader like an oscilloscope be the most energy efficient setup, or would reading the charge and discharge time of the variable capacitor be more efficient. The linear displacement of the device is likely to stay consistent for long periods of time, meaning that there will be little change for long amounts of time, then rapid change, then back to nothing. So the device only needs to read the discrete values, not a continuous stream of testing, this is not critical so ignore if it complicates the issue. This is a prototype portable IOT design, so it needs to be battery powered and somewhat efficient.
Any advice or direction would be greatly appreciated,
Thank you all.
You need to add far more detail.
What exact variable capacitor?
What frequency dou you expect? (Hz, kHz, MHz)
My guess is that a battery operated ossiloscope cannot be run for days on one set of batteries...
A micro controller could.
Without continious monitoring... how do you expect to catch the moment something happens?
DIY thingies are often brought to market by brands like adafruit. They often have a library with examples to setup a basic measurement.
Start from there...
The capacitor operates in an identical fashion to a sliding variable capacitor. The total area of overlap will be no more than 36cm, so the total capacity of the capacitor is likely to be in the nanofarad range. I was going to use a pulse generator on like a 15 milisecond delay between pulses. So I am thinking that tying the frequency to the pulse generator would make for a workable setup. This would make for a 66.6 Hz setup.
I was going to use a 3.7V 150mAh Lipo Battery for power due to size constraints.
Please post a dimensional drawing of the variable capacitor.
The total area of overlap will be no more than 36cm, so the total capacity of the capacitor is likely to be in the nanofarad range
Area is measured in squared units, like cm^2, e.g. 6cm x 6cm = 36cm^2.
If you want to measure nano Farads, you need kHz, not Hz...
Please add a link to some info on your variable capacitor...
To do that you need an oscillator with the frequency controlled by your capacitor. Do you have such a device?
Right, sorry I am just lazy when typing. The fixed area is 12cm x 3cm, so 36cm^2. The other electrode is a spring that is depressed to get more area of overlap. I don't know the best way to calculate this value, other than using percentages. I am going to assume that at the minimum compression of the spring the total area of overlap is roughly 8%, so 2.88cm^2, and at maximal compression it is at 80% coverage due to gaps between splines, so 28.8cm^2. There is a very small air gap, and I am using heat resist tape as well as a heat resist paint on the spring as a dielectric. I have not measured the area under the sawtooth on an oscilloscope to get the charge capacity yet because it is a very tight space, and the equipment I have is not great.
Hope you like ms paint, this is not to scale, nor a design document, the copper foil wraps most of the way around the spring, and is not as shown in the sketch
I am very new to hardware so I am unaware of the electrical values required in measurements, and this is a homemade setup, not bought. I am retrofitting a design to implement a measuring and digital readout.
I can buy one, any recommendations. Size is a major factor. If there is a better way to get a readout from a capacitor I would prefer to keep parts to a minimum. I'm new so please excuse my ignorance.
Guess you need to measure the capacitance.
The capacitance is a function of the area and the distance...
Once we know the capacitance we can think of how to measure the capacitance.
Certainly. Some digital multimeter will measure capacitors. Get one and try it!
Sorry, I don't know what that diagram is supposed to represent. What are the two independent plates of the capacitor?
Two 6cm x 6cm plates separated by an air gap of 0.002 cm (0.02 mm) will have capacitance of about 1.6 nanoFarad. Very small separation!
See Capacitance Calculator • 66pacific.com
That is what I guessed. It is not easy to reach 100 nF...
Using the calculator provided, the minimum capacitance is calculated to be:
Capacitance: 1.27 picofarads
Input Values:
Area: 2.88 square centimeters
Separation distance: .2 centimeters
Number: 2
Dielectric constant: Air: 1.001
The maxamum capasatance is:
Capacitance: 12.7 picofarads
Input Values:
Area: 28.8 square centimeters
Separation distance: .2 centimeters
Number: 2
Dielectric constant: Air: 1.001
Oh, sorry, I have one, I meant in the wiring diagram for the computer to read. I have tried to use my multi-meter to measure the capacitance of this but was getting zeros, I assumed my janky DIY setup wasn't able to hold enough charge to be measured by the multi-meter.
Check the meter specifications. Likely the capacitance is too small for it to measure. Check with a known capacitor to see how close the meter reads.
What material are you using to insulate the plates form each other?
Yeah just checked my multi-meter only has the resolution for 10 picofarad, and I never tested the capacitance at full spring compression. Even then it would have barely been within range. It was a cheap multi meter so I'm not at all surprised.
Just to clarify I have never worked with hardware before so I was operating under the assumption that nano was smaller than pico, so noob mistake on my part. sorry for the confusion.
Are sure you have a capacitor and not a short circuit that you are making? Measure a known capacitor and while measuring, connect your linear capacitor in parallel with the know cap and see if your meter flickers a bit.
10 pF is roundabout nothing...
I would hope your capacitor has more capacitance than that.
And I am almost certain that your meter will be able to measure larger capacitance (as measuring a larger capacitance is easier).
Can you make a photograph of your meter?
And maybe also a photograph of your setup?
