sensor inductor frequency measurement?

I have a sensor which uses a moving inductor core to give a proportional output of frequency. I believe it is something like this: - the inductor coil is pin 1 and pin 3 - there is a capacitor between pin 1 and pin 2, and another capacitor between pin 3 and pin 2.

my capacitors measure 44 uF each but the info I have mentioned 22 uF? It says 5vdc on it. It apparently is supposed to output a frequency around 25 kHz. They are a very common washing machine water level sensor, 6601ER1006A or DN-S14T-H.

Can anyone suggest how I can read the output with an arduino?

Thanks! Bryan

Diagram? Datasheet for sensor?

i have a .jpg drawing that I tried to attach but it would not upload. Trying to figure out how to upload now.

The diagram shows 22nF, not 22µF(*). Two 44nF is series is 22nF. The capacitor is tapped to allow driving with a Colpitts oscillator circuit.

3mH and 22nF will oscillate around 20kHz. The variation in inductance will shift the frequency up and down which can then be counted by a microcontroller after the oscillator.

(*) µF values would require electrolytic capacitors which are not at all stable in value and no use for measurement.

so sounds like an oscillating circuit is required. Is this feasible with an arduino?

Thanks

Did you look to see what a Collpits oscillator circuit is?

Paul

Yes, I looked up colpitts oscillator circuit. Forgive my ignorance, was wondering how much of the oscillator circuit the arduino could do ... After reading again, there is a Radio Frequency Choke in there which I am quite sure the arduino cannot do.

That means I would have to build the oscillating circuit from scratch which is beyond my capabilities.

Shame because these water level sensors would be ideal for my application and are readily available for free.

bryanb334: Yes, I looked up colpitts oscillator circuit. Forgive my ignorance, was wondering how much of the oscillator circuit the arduino could do ... After reading again, there is a Radio Frequency Choke in there which I am quite sure the arduino cannot do.

That means I would have to build the oscillating circuit from scratch which is beyond my capabilities.

Shame because these water level sensors would be ideal for my application and are readily available for free.

Yes you would have to build it from scratch and it is well within your capability. Just get the parts and try it.

Paul

Paul_KD7HB: Just get the parts and try it.

Paul

I have not found any specific info on which transistor, what resistor values, or even what a radio frequency choke is. If you can point me to a schematic with some specific components, I would like to try building one ...

Back on your first post you wrote that you have a sensor that does all this and you only need to read the frequency. What exactly do you have and does it work?

Paul

bryanb334: Yes, I looked up colpitts oscillator circuit. Forgive my ignorance, was wondering how much of the oscillator circuit the arduino could do ...

It can't, its not an analog amplifier, its a microcontroller.

bryanb334: I have not found any specific info on which transistor, what resistor values, or even what a radio frequency choke is. If you can point me to a schematic with some specific components, I would like to try building one ...

Ever heard of this modern-day oracle called Google? If not, put that name in your favourite search engine. It'll be able to give you numerous schematics of a Collpits oscillator. They're pretty easy to build. Just about any small signal transistor will do. Just make sure the output voltage is high enough for the Arduino.

The inductor/choke you have already of course, and 25 kHz is not what most people would call RF.

just read a post where it talks about an arduino using a PWM output to test the frequency input. Would this work to drive the LC sensor?

https://www.avdweb.nl/arduino/timing/frequency-period-counter

Thanks again

wvmarle: Ever heard of this modern-day oracle called Google? Just about any small signal transistor will do. Just make sure the output voltage is high enough for the Arduino. The inductor/choke you have already

This is not very helpful for a newbie. I HAVE done lots of googling and have learned lots, but I have tried to buy transistor before and there is a ton of choices and not understanding all the details has resulting in me ordering the wrong ones on two other projects. Incredibly frustrating. How do I make sure the output voltage is high enough for the arduino? The inductor is part of the sensor but the RF Choke I do not have.

If you are not interested in helping a newbie then why be condescending?

Not being able to find suggestions for part numbers and resistor values is nonsense, if that’s the case you didn’t do your homework. As said, just about any small signal transistor (PNP or NPN depending on your circuit) will do fine. Indeed there are a lot. See what you have in your parts bin, or what your favourite supplier has available. Of course you see different values in different circuits, sometimes it’s simply not critiical, sometimes there are other reasons. Read the explanations that go with many such circuits. Make sure you understand the circuit you intend to build.

Why do you think you even need this RF choke?

What circuit does the manufacturer of that sensor suggest you to use?

For this kind of circuits, when developing it’s best to connect a scope to see whether it oscillates, at what frequency and what amplitude. You can of course just build the circuit, connect it to an input pin, and hope you get a useful signal. If it works just like that, great. If it doesn’t, you’re working blind.

wvmarle: Why do you think you even need this RF choke? What circuit does the manufacturer of that sensor suggest you to use? For this kind of circuits, when developing it's best to connect a scope to see whether it oscillates

I think I need a RF Choke because the circuit diagram that I found said to use one ...

I cannot find any info from the manufacturer of the sensor, no datasheet, no anything, and this is not for lack of looking. It must be proprietary or something. I would love to be proved wrong though!

I don't have a scope and, as mentioned, I am a newbie which is why I am asking questions here.

Thanks for trying to help though!

Bryan

Looking at the two sensors you linked to in your original posting, I see they are simple diaphragm switches. A diaphragm is moved by the pressure to operate a micro switch. Where did the idea of a device that uses an oscillator to generate different frequencies come from?

I have larger sensors just like those that were used in equipment to ensure the ventilation system is working before the equipment can be operated.

Paul

These sensors are the new type which do NOT have a microswitch. They have a diaphragm that moves a ferrite plug within an inductor which alters the resonance of the LC circuit. If you look at the diagram that I linked to, you will see the details of the sensor. They are commonly used in NEWER washing machines to give a proportional indication of the water level as opposed to the older type that just have a microswitch indicating a specific level.

Ok. And I guess you gave the link to the older ones because you have no link to even a picture of the new ones? How does that help?

Paul