OK, you have a few things here which will be a problem. Going back to the image in your first post they show the bolt, we can call it a bolt, moving in and out of a coil so yes, two wires out. A best guess here is that, as mentioned, the inductance of the coil will change as an iron core, the bolt, is moved in and out. Back to this later.
You mentioned "trim" and also a boat came up along with underwater. So what you have is a boat with trim tabs and the idea here is to know the position of those tabs in the pilot house or simply put drivers seat. The trim is set depending on water conditions, weight on the boat and weight distribution on the boat. The trim tabs move on an axis so we can say X number of degrees of trim or express the trim as a percentage such as 0 to 100% trim. Now earlier you mentioned:
First thing to understand with this would be that is not accuracy but rather the resolution. Resolution, in simple terms can be defined as the ability to read an instrument or of an instrument to be read. In this case with a 10 LED display each LED represents 10% of trim. So the best we can resolve is 10% increments of change. Accuracy is a qualitative term, the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard. Ideally we want accuracy with a high resolution.
It would be helpful to know how the LED display is driven. Setups like this are normally driven with a voltage level fed into a simple chip like the LM3914 Dot/Bar Display Driver. With what you mention they are getting a signal somehow. Since they offer a position display like this there is a good possibility the signal from the cylinder is as good as it gets. Meaning the accuracy of the signal to work with will only afford a trim position to a given degree of accuracy or uncertainty, allowable error.
The only way to start is knowing what the inductance of those two wires actually is. Find the cable from the trim tab, locate those two wires and using a LCR Meter (Meter to measure inductance) measure the inductance with zero trim and 100% trim. Then as mentioned build an oscillator circuit around that. The oscillator out is fed into a F/V (Frequency to Voltage) converter and scaled as 0 to 100 percent in your code. This is not a simple task or design to just wing it.
Now as to using a Teensy 4.0 Version. I have never used one but my read is that it uses a 16 bit SAR (Successive Approximation Register) ADC. Additionally the analog input pins use a 2.56 Volt internal reference unless an external reference is selected in the code and applied to the chip. So stand alone, no external reference, the analog inputs are 0 to 2.56 Volts maximum. While saying 16 bit ADC sounds real nice the ADC process is only as good or accurate as the chips internal reference.
Internal 2.56V Reference
The internal reference allows you to measure specific voltages, since it will remain at (approximately) 2.56 volts, even when the power supply voltage changes. The ADC input range will be 0 to 2.56 volts.
Atmel only guarantees the internal will be between 2.4 to 2.8 volts, which is ±7.8% error. There is also no specification for it's stability over temperature changes. Often it will perform quite well, but there is no guarantee.
The internal reference is good enough for many basic applications. Often you can calibrate by measuring a known accurate voltage, and store the internal reference's actual voltage in your code or in EEPROM, then use it in calculations to correct for the error.
External Reference
When you need accurate voltage measurements, an external voltage reference chip is required. Because it affects the entire range of the ADC, the accuracy of your measurements depends on the accuracy of the voltage reference. Even inexpensive reference chips outperform the internal reference. For example, a LM385BLP-2.5 has ±1.5% initial accuracy (no calibration and adjustment), and a LT1009 has ±0.2%, both with very good stability over temperature changes.
You can buy voltage reference chips in different voltages. 4.096 volts can be nice, because it gives a larger signal range, and each step of the ADC is exactly 4 mv. The external reference must be less than or equal to the power supply voltage.
You can see that to effectively use the chip an external reference is required. Again I never used a Teensy but have used plenty of ADC chips and Arduino Micro-Controllers.
Anyway all of this is moot unless the inductance range from the sensor is known. However, this is what you are up against with what is known.
Ron
@Thomas Prüfer@TeeKay6
You sound almost angry.. ;-) look at the picture attached. No more information available. The indictors are mounted under the waterline. So not so easy with 5 tonn of boat to take them apart to check details. There no information provided by the producer even. I send them some quetions regarding the details but they can't or didn't wanted to answer.
How ever, I didn't expected to get a full developed cirquit of you guys, really not. I am looking for ideas what could be the solution. Then more try and error to finally come toa result which will be usable.
So the coil is cast in platic, not even visible.
Actually what I am trying to do is backward engeneering of this device since the small electronic where the sensors should be connected to is exactly doing what I try to build. There just one thing why I can not use the one which is delivered in this set. Calibration! To calibrate the sensors I would need a multifunction display from Lowrance which costs aboutt 2T usd. This cal. needs to be done just once initially before the device is starting to send the information to the NMEA2K bus. The poin is that I am using a different (from y view much better) Navigaation device from Raymarine which have also costs 2.5K usd. So you may understand my problem, spent 2K for one 5 minute ontime job?!
I have build this device for other sensors already, working just fine. The only thing I have problem with that I do not know how to interface a coil with a moving bolt inside to provide a analog voltage.
May the idea from BobTPH is not so bad. The frequency I could then tranform to voltage using a LM2907 or 2917 (used before for engine RPM).
I am unable to see how the sensor you posted a photo of can possibly have a range of linear travel up to 100mm if it is indeed simply a coil with a movable core. The coil length would have to be a minimum of 100ms length and I see no place in the photo for that coil to exist. Do you have other photos showing more detail? Do the green and red cables contain only two wires each (and what is diff between red & green cables)?
