water sensor using a pressure sensor - Page 1
Forum section: electronics / projects

author: electricianjay
author_rank: Newbie
timestamp: January 05, 2014, 01:07:30 pm
content: I'm a diver. I want to make a watch that gives me a rough idea of my depth.I'm thinking of using one of these.https://www.sparkfun.com/products/retired/9694.Sealing it inside a small container. I am not too sure about the technical stuff about air pressure water pressure but I'm thinking as I dive deeper the air pressure inside increases. Depending on how well built the container is the air pressure will be less for a well built/strong metal container. Calibration of the device / a crude lookup table will be required.Am I going about this the right way?Eventually want to make something that looks like a watch.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 05, 2014, 01:25:35 pm
content: I can't see why this wouldn't work, calibration is going to be your biggest challenge though, there's not going to be an awful lot of change in pressure, so you're going to have to make sure you get it right. The link seems to be dead though...

author: Rerouter
author_rank: Super Contributor
timestamp: January 05, 2014, 01:49:39 pm
content: Your link appears broken, so I'll assume your looking at a barometer sensor, in that case, all that spark-fun sells will not fit the bill,every 10m, the pressure increases by 1 atmosphere, or 101KPa as an average, considering those cells max out at 115KPa you wont get far there, (you casing will not be good enough to reduce the effects for even 10m)your best bet that i can see here is to use something like thishttp://au.element14.com/honeywell-s-c/nscdann150pgunv/pressure-sensor-0-to-150psi/dp/2065477and to use an op amp so scale and gain the signal into your 20-60psi (0-30m) dive rangeas a good suggestion for your pressure interface, take the rubber out of a bottle-top, and fit that inline with the pressure sensor, that way you can measure true pressure, not something that changes with temperature, and that rubber is generally good for a differential of 40psias for calibrating, you can use a fixed height of fluid, (Density*Gravity*height ~ 1*9.81*(meters) = Kpa)

author: Unknown
author_rank: Unknown
timestamp: January 05, 2014, 03:49:29 pm
content: https://www.sparkfun.com/products/retired/9694Extra . removed.

author: AlfBaz
author_rank: Super Contributor
timestamp: January 05, 2014, 04:10:17 pm
content: I wonder if the LDC1000 could be used in this particular applicationIf you build an enclosure out of appropriately flexible material, movement of a slug placed in proximity to the pcb coil may be sufficiently accurate and repeatable to be usefulhttp://www.ti.com/tool/ldc1000evm

author: calzap
author_rank: Frequent Contributor
timestamp: January 05, 2014, 07:06:07 pm
content: Jay,If you are interested in doing this as a fun or learning exercise, carry on. If you want to have a product to use now, you can buy a snorkeling watch from Amazon for less than US$100.Mike in California

author: calexanian
author_rank: Super Contributor
timestamp: January 05, 2014, 07:42:19 pm
content: You may want to have a look at these. We are using them in a water pressure sensing application.Honeywell 26PCFFD2GThis gauge is 100 psi but they have them all the way down to a few inches of water column sensitivity. They are a true wet gauge so all you gota do is drop them in. No back pressure required, but if you wanted to have the ability to have a back pressure that are avaliable in a differential version that is Wet/Wet which means they can tolerate liquid on both sides. They are a bridge sensor and the output is on the order of 250mv. We use a MAX4460 in basically its application note circuit. They say they want to be run at 10 volts across the sensor, but we run both the sensor and amplifier at 5 volts and have found them to be very stable.

author: electricianjay
author_rank: Newbie
timestamp: January 06, 2014, 02:23:12 am
content: Just found this:MC5535c pressure sensor module. Application is for "diving computers"Looks good just am trying to sort out how to expose the sensor to water leaving electronics in an enclosure. Datasheet says using a O-ring on outside but I just cant see how that can seal it from outside water pressure.There is a person using arduino. He has one working beit a bit bulky. I invision on making something the size of a normal dive watch. I just need a cnc mill, tempered glass and some metal. I'v got a long way to go but I'm giving it a go as I'm passionate about diving and electronics. :phttps://www.adafruit.com/blog/2012/10/01/diveduino-diy-arduino-based-dive-computer/