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[on:]

Hi
I´m using a Arduino MEGA as ECU for my DIY gasturbine. I´m also going to use it to log data during the runs and that´s where the senders come in.
I need 6 senders to read air, oil and fuelpressures.
I´ve bought a 5$ automotive replacement oilpressuresender to do some tests with but since I´m a rookie in both programming and basic electronics I don´t get the results that I want...

I would like to analogRead a value that is as close as possible to linear to the rised pressure in Bar. I´ve tried with a voltage divider but i´m not sure if I´ve used the right value... think i tried with a 150ohm.
The resistance of the sender is ~
At 0 Bar - 0.22 Ohm
1Bar -      22Ohm
2Bar -      41Ohm
3Bar -      55Ohm
4Bar -      73Ohm
5Bar -      92Ohm
6Bar -      109Ohm
7Bar -      124Ohm
The pressures will only be logged for now so the accuracy is not to critical...
Please give me some ideas how to solve this.

Or if You know of any other rather low cost pressuresender please let me know

[Reply #1 on:]

I am interested in this because I always wanted to build a gas turbine but never knew where to start. I saw some designs using a old car turbo. It seems like a pulse jet is easier but more noisy. The only reason I wanted build a gas turbine was for the noise it makes though, how cool would it be roaring through the suburbs on a jet powered go cart.  8-)

If you could provide more info etc I will help you as best I can with the electronics.

What brand and type of pressure sender are you currently using, where are you putting it etc etc

[Reply #2 on:]

If you connect your sensor like this:

+5V --> sensor --+--> ---/\/\/\/\---- --> gnd
                         |        (resistor)
                         v
                     analog pin

You should be able to use analogRead(pin) to read the voltage at the middle of the voltage divider. Since the sensor appears to be pretty linear, the voltage drop should be linear, too, since the resistor's value does not change. The value on the pin will go down as the pressure goes up, and the minimum value will be something greater than 0, but you should be able to use the map function to get a value that increases as the pressure increases (the from range will be 1023 to ~100 instead of ~100 to 1023).

[Reply #3 on:]

I´ve connected it like PaulS sketch but i connected the sender to ground and the resistor to +5v. Can this be my problem?
The readings i got when i hooked it up like that and with a 150 ohm resistor was... (The data type is "int")
at 0bar   = Value  9
1bar   =  139
1,5bar = 195
2bar   =  230
2,5bar =  260
3bar   =  293
3,5bar = 326
4bar   =  355
4,5bar = 383
5bar   =  396
5,5bar = 419
6bar   =  435
6,5bar = 454

the step from 0 to 1 Bar is 130 points while the step from 5,5 to 6,5Bar is 45 points...

Is it possible to straighten the "curve" up with the value of the resistor??
Our project homepage is http://mobackenracing.se it´s in Swedish thou...
Many thanks!

[Reply #4 on:]

I tossed out the first point (0 bar), and plotted the remaining points. The curve is pretty linear.

From the point at 1.5 bar to the point at 4.5 bar, the curve is very straight.

As a first approximation, I'd treat the curve as linear from 0.5 bar on.