Measure water depth using a piezoresistive pressure transducer

Hello everyone.

I want to make a device which I can mount onto say an ROV to measure the water depth through pressure readings.

  • I've got this sensor.
  • This is the datasheet.

And I'm using an RFduino. The moment the device surfaces, I want it to transmit the pressure readings it recorded to a Bluetooth receiver. That I can program, the problem is that I can't find any API or code examples that resemble my 4 wire piezoresistive sensor.

So I've got 4 wires:

Color

Function

  • Red: Supply +
  • Black: Supply -
  • White: Output +
  • Blue: Output -

Can you guys point me in the right direction? If there are similar code examples (only to read the sensor data) that I'm unaware of, that would be perfect as well.

Thanks,
Hendrik

You need a wheatstone bridge circuit, similar to that used with strain-guages and load-cells, only it doesn't
need to be nearly as sensitive - so any 5V load-cell amp board with programmable gain might do, with
a gain set to 50 or 100 or so.

You need something like an instrumentation amplifier to increase the 100±20mV span up to 5v to get best resolution from the Arduino's analogue input.
Or something like this load cell amplifier.

The pressure sensor that you linked to measures up to 1.6MPa / 16bar.
This is equal a water depth of around 160m.
Is that the range you require?

JohnLincoln:
The pressure sensor that you linked to measures up to 1.6MPa / 16bar.
This is equal a water depth of around 160m.
Is that the range you require?

More or less. 160m might be a bit too deep, but not impossible for an ROV.

MarkT:
You need a wheatstone bridge circuit, similar to that used with strain-guages and load-cells, only it doesn't
need to be nearly as sensitive - so any 5V load-cell amp board with programmable gain might do, with
a gain set to 50 or 100 or so.

Ok thanks.

JohnLincoln:
You need something like an instrumentation amplifier to increase the 100±20mV span up to 5v to get best resolution from the Arduino’s analogue input.
Or something like this load cell amplifier.

Some load cell amplifier circuit it shall be. I’ll keep you guys posted.

If I were to use this sensor, I could directly read the data right?

Since it has digital output (I2C). Appart from being more expensive, doesn't that sensor look like the better choice?

That transducer is an unmounted, surface mount (SMD) part.

How would you mount it, protect all the electronics from high pressure water intrusion and still measure the pressure?

I'd agree that a digital sensor like the MS5837 is the better choice, taking total time and effort into account. I might go with the MS5803 instead to get the SPI interface if the size isn't an issue, but that's just me. In fact I think sparkfun uses one of them in a (pricey) breakout board. Both models come in a number of pressure ranges (higher max pressure = more money). Mounting is pretty straightforward and at lower pressures (say below 6 bar - 50 meters where my dive gear goes) the tolerances aren't very critical for the O-ring fit. I've done some pretty sloppy jobs! However, it IS critical that (1) the bore of the housing (the mating surface for the O-ring) be smooth and (2) the sensor is mounted straight - not at angle in the bore. Have fun.
Mike