Diving computer wireless pressure sensor? - Page 1
Forum section: electronics / general

author: nardev
author_rank: Unknown
timestamp: February 03, 2020, 02:05:19 pm
content: In past few years i notices that very handy bottle pressure sensors appeared. I just can't find any info how that "underwater wireless" works.I know several ways how some data could be transmitted but it doesn't fit this thing at all.Does anyone knows more about that?It usually looks like this, the pressure sensor is attaches at spare valve and the data is somehow sent to a computer.

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 03, 2020, 02:46:08 pm
content: Does it transmit while being under water or does it work when out of water. Under water, most of the RF energy will get attenuated quickly within few centi-meters.Ultrasonic is something which can work under water. Use some high frequency ultrasonic transducer for communication. The computer will also have a ultrasonic receiver which is immersed in the water.

author: nardev
author_rank: Unknown
timestamp: February 03, 2020, 02:47:56 pm
content: Under water of course. You need to track how much air you have in the bottle.

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 03, 2020, 02:51:48 pm
content: Mostly an accoustic link.

author: nardev
author_rank: Unknown
timestamp: February 03, 2020, 02:57:01 pm
content: But it can be pretty messy under water. The speed of sound traveling under the water can be pretty nasty to process the signal. Can't find any proof for that, also, this devices have to stand 300bars pressure so i don't know how they would make sound and "send" the data with such an enclosure needed for that pressure.

author: m98
author_rank: Frequent Contributor
timestamp: February 03, 2020, 03:12:31 pm
content: The FCC, your favorite resource for low-effort industrial espionage:https://fccid.io/RYP21162It transmits on 123 kHz, PSK modulation, 25 dBm transmit power, using a ferrite coil antenna.When you look at the internal pictures, it probably uses a modified industrial pressure transducer. The housing doesn't need to contain the tank pressure, it "only" needs to withstand external water pressure.

author: nardev
author_rank: Unknown
timestamp: February 03, 2020, 03:14:19 pm
content: Quote from: m98 on February 03, 2020, 03:12:31 pmhaha, great, thnx. I hope some day i'll see disassembly of this sensor.

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: February 03, 2020, 03:15:05 pm
content: Slightly OT:I would never ever want to rely on some mumbo-jumbo wireless tech for something that is vitally important.Exhibit 1:https://www.suunto.com/Support/recall/suunto-wireless-tank-pressure-transmitter-and-suunto-tank-pod-recall/

author: m98
author_rank: Frequent Contributor
timestamp: February 03, 2020, 03:23:30 pm
content: Quote from: frozenfrogz on February 03, 2020, 03:15:05 pmSuunto is a pretty reputable manufacturer of diving instrumentation, and product recalls for safety-critical products aren'tthatrare.

author: nardev
author_rank: Unknown
timestamp: February 03, 2020, 03:29:33 pm
content: Quote from: frozenfrogz on February 03, 2020, 03:15:05 pmWell, i think this is just a first generation of products of this kind so they will be improved by the time.Also, very handy reason for having such a devise is so that the instructor can monitor the pressure of the students or "fun divers". Such dives are usually pretty safe, very well controlled and thus not very dangerous.With such monitor, the instructor doesn't need to stop dive and ask everyone for the remaining air. On top of this, everyone can have it's own monitor which is not wireless but a hose connected directly to a bottle.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 06, 2020, 12:12:40 am
content: It's also possible to get a (lossy) transmission line with the metal braid in the hose as one conductor and the water as the other. Or (even more lossy) the diver's body as one conductor and the water as the other, with the diving suit keeping the impedance between the two sufficiently high.

author: matts-uk
author_rank: Contributor
timestamp: February 11, 2020, 06:22:02 pm
content: Quote from: frozenfrogz on February 03, 2020, 03:15:05 pmThe recall was for a mechanical issue, nothing to do with wireless mumbo-jumbo.When a wireless transmitter fails the display turns to garbage and provides an obvious and immediate indication that action is necessary. When mechanical guages fail they tend to stick indicating more gas than is actually available. Over a 28 year period with over 2000 dives I ended up performing three rescues as the result of faulty mechanical guages. Personally I try to maintain a mental picture of how much gas I am breathing and how much I still have available - kept me alive a couple times :eekQuote from: nardev on February 03, 2020, 03:29:33 pmThe transmitters have been around for 25 years. From what I recall Uwatec were the first to introduce them on the AirX in the mid 1990s. I still have one knocking around somewhere.QuoteI am a qualified scuba instructor and you just triggered meMonitoring students air with a remote device helps the instructor to cover their own backside but it is not teaching the students to dive. Stopping and checking guages is how students learn they need to do it themselves with their dive buddy. I am very much of the opinion that would-be divers should learn the basics of life support before they even attempt to have 'fun' underwater.QuoteAhh but...Failure pointsOff topic. Sorry.

author: nardev
author_rank: Unknown
timestamp: February 11, 2020, 06:29:02 pm
content: Well, my understanding was that an instructor or lead diver gets fast and simple info about status in a whole group. Which is pretty convenient.btw. i have been diving for 5-6 years only and i haven't seen those wireless transmitters before just a few years. maybe it's becoming bit more popular lately or bit more affordable.Anyway, would be nice to see "take apart" video by @dave of a such a device. Old or new.