Hey everyone,
I know this is VERY basic, but Im confused.
I have 3 resistive sensors which are installed in a machine i need to read.
All the tutorials I see say hook up the sensor to +5v and ground with the input taped in the middle.
I only have 1 wire for each sensor, they all read resistance to ground, so do I just wire 5v to my input aswell as the sensor lead and let the sensor drain off the 5v as it changes?
Not quite. Each individual sensor wire will have to have it's own series resistor wired to +5vdc. The junction of the sensor wire and the new resistor will wire to an individual analog input pin.
The size of the new resistors depends on the range of minimum to maximum resistance of your sensor. If you don't have a data sheet showing this range of resistance change, you will have to use a ohm meter and manipulate the senser input and read the ohm value change for the range desired.
Lefty
ok, i think I have a general idea of how to hook it up.
Could you please explain how to figure the fixed resistor size?
my sensors are 0-90 ohms and 54-1254 ohms
For the 0-90 ohm sensor(s) if you use a 100 ohm fixed resistor the resulting analog voltage measured will range from 0 volts up to 2.37 volts. For the 54-1254 sensor(s) a 1,000 ohm fixed resistor will measure from .26 volts to 2.78 volts. You can scale/correct these ranges in software once you know the raw counts of range.
What kind of sensors are these anyway?
Good luck
Lefty
I really appreicate your help!
I have been trying to figure this out all day
Maybe a silly idea but, I have a trans-am with a bad instrument cluster
I am looking into making a arduino replacement.
I just saw a the wav shield so I could make it talk too!
I figure it is as good as any 1st project, a good way to learn
Could you please explain how you came up with the values, I would like to understand how to do it, rather than relying on the community
Thanks
Could you please explain how you came up with the values, I would like to understand how to do it, rather than relying on the community
Thanks
It's just using iterations of ohm's law. You calculate the the total series resistance of the sensor (at one extreme range value) and the fixed resistor by addition. Then you calc the series current by I = E(5vdc) divided by the total series resistance. Then calculate the voltage drop across the sensor resistance by multiplying E = I X R. You have to do the same calculation for when the sensor is at it's other extreme value. And of course because you have sensor(s) with different values you have to do the whole thing for the other sensors values. Making the fixed resistors approx equal the the maximum sensor's resistance gives you a useful swing in output voltage range.
What we have here is a basic voltage divider network with one leg (the sensor) that is variable resistance.
Lefty