Hi,
I'll start off with saying that this is most likely an obvious question, I've decided to teach myself some electronics as a hobby and this is my first attempt at application.
On our property we have a number of water tanks. Each tank fills and empties at different rates. When the tank reaches a certain level it also must be automatically discharged into either non-full tanks or down the drain.
I figured that it would be a good first project to use an arduino unit to measure the tank level with a differential pressure sensor which would both submit the information to the internet and control a number of relays for valves.
I actually managed to find someone who is doing the same project with the same sensors:
http://www.practicalarduino.com/projects/water-tank-depth-sensor
So I figured instead of going from scratch, I'd use his circuit diagram as a guide:
http://www.practicalarduino.com/schematics/water-tank-depth-sensor-schematic.jpg
From what I can work out, its an instrumentation amplifier with some sort of offset.
So I build the circuit with identical op-amps and similar resistors and I've come across two problems which are occuring in practice on my breadboard but not on the software I'm using to simulate it:
1) Minimum voltage seems to be 0.76V no matter what the offset is set to.
2) Maximum voltage seems to be 2.5V
I'm thinking '1' is probably the minimum the op-amp can be taken down to as it seems to be close to a diode drop. This is not a problem as I can get the Arduino unit to offset it, though it would have been nice to get the full 0-5V range.
'2' I'm a little baffled by. Looks like saturation. I'm wondering if it has something to do with the voltage divider used for the offset? The voltage divider is producing about 2.08 V. I'm not even sure if its necessarily the best way of achieving the offset either.
Ideally, for the sake of resolution (only 1024 points), I'd like to get it spanning as much of the 0-5V range as possible.
The datasheet for the pressure sensor can be found here:
http://pdf1.alldatasheet.com/datasheet-pdf/view/86195/MOTOROLA/MPX2010DP.html
It apparently produces a voltage difference of 25 mV at its maximum operating conditions, the average value being approximately 1/2 Vcc (using 9V battery so ~4.5V). The offset is to allow one to correct for the small voltage difference when pressure is equal (I think). At the moment I've been using the offset to ensure that the 0 m depth corresponds to a voltage > 0.76 as it doesn't detect any change in depth for anything under 0.76 V.
Any help will be much appreciated!
Thanks,
Simeon
-----
On a side note. Is there any trick to estimating the length of wire needed based on the number of squares? I'm finding I'm making a guess, being totally off and then trimming it, rather slow.
I'll start off with saying that this is most likely an obvious question, I've decided to teach myself some electronics as a hobby and this is my first attempt at application.
On our property we have a number of water tanks. Each tank fills and empties at different rates. When the tank reaches a certain level it also must be automatically discharged into either non-full tanks or down the drain.
I figured that it would be a good first project to use an arduino unit to measure the tank level with a differential pressure sensor which would both submit the information to the internet and control a number of relays for valves.
I actually managed to find someone who is doing the same project with the same sensors:
http://www.practicalarduino.com/projects/water-tank-depth-sensor
So I figured instead of going from scratch, I'd use his circuit diagram as a guide:
http://www.practicalarduino.com/schematics/water-tank-depth-sensor-schematic.jpg
From what I can work out, its an instrumentation amplifier with some sort of offset.
So I build the circuit with identical op-amps and similar resistors and I've come across two problems which are occuring in practice on my breadboard but not on the software I'm using to simulate it:
1) Minimum voltage seems to be 0.76V no matter what the offset is set to.
2) Maximum voltage seems to be 2.5V
I'm thinking '1' is probably the minimum the op-amp can be taken down to as it seems to be close to a diode drop. This is not a problem as I can get the Arduino unit to offset it, though it would have been nice to get the full 0-5V range.
'2' I'm a little baffled by. Looks like saturation. I'm wondering if it has something to do with the voltage divider used for the offset? The voltage divider is producing about 2.08 V. I'm not even sure if its necessarily the best way of achieving the offset either.
Ideally, for the sake of resolution (only 1024 points), I'd like to get it spanning as much of the 0-5V range as possible.
The datasheet for the pressure sensor can be found here:
http://pdf1.alldatasheet.com/datasheet-pdf/view/86195/MOTOROLA/MPX2010DP.html
It apparently produces a voltage difference of 25 mV at its maximum operating conditions, the average value being approximately 1/2 Vcc (using 9V battery so ~4.5V). The offset is to allow one to correct for the small voltage difference when pressure is equal (I think). At the moment I've been using the offset to ensure that the 0 m depth corresponds to a voltage > 0.76 as it doesn't detect any change in depth for anything under 0.76 V.
Any help will be much appreciated!
Thanks,
Simeon
-----
On a side note. Is there any trick to estimating the length of wire needed based on the number of squares? I'm finding I'm making a guess, being totally off and then trimming it, rather slow.