Does anyone out there have any experience of using any ultrasonic sensors that could be waterproofed (or are already).
I am building an automated sub for a uni project and have, as yet, only been able to find serious commercial units that cost a packet.
Any ideas would be appreciated.
(the range does not need to be great - probably <10m would be fine)
Try a marine supplier or yacht chandler, they should provide exactly what you are looking for - ie ultrasonic transducers that are guaranteed totally waterproof (they are used in echo location depth sounders). I am unsure of the frequency, I think it is around 22kHz that they use which is not the "normal" 40kHz that air ultrasonic devices operate on; the lower frequency being required to achieve adequate transmission through water.
jack
Alternatively you could try bonding a piezo sounder module to a piece of glass or acrylic and seal the back surface with silicon or similar type agent
jack
You might be able to use parts off of something like below.
I use these and have been using these for years. They are great for outside work.
You need to look at the "WR" and "WRC" models.
I use these and have been using these for years. They are great for outside work.
You need to look at the "WR" and "WRC" models.
only been able to find serious commercial units that cost a packet.
The waterproof maxbotix modules in my mind cost a packet whether they're classed as commercial or not 
True, the ~$100 is a bit of an ask, but you wont find a cheaper or more reliable waterproof sensor for the price (either home made or readymade). If you can find one let us know. I've been looking for years.
But it is quite a jump from the very reasonable ~$25 for the non-waterproof model to the ~$100 for the waterproof one. On the other hand it pales to the prices charged for similar units from SICK, Honeywell et al.
P.S. I have no shares, friends or affiliations with Maxbotix.
Yeah I suppose I agree with that. They are all rather expensive 
P.S. I have no shares, friends or affiliations with Maxbotix.
Heh, I would have mentioned them if you hadn't 
You said "sub" - you need sonar, not just weatherproof sensors.
I recently bought one of these:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220698970051
$64 delivered in the US. It comes with 4 wires - power (12v), ground (must share ground with Arduino), data in (tape it and ignore it) and data out (this is RS-232 NMEA at 4800 baud). you need a level shifter:
to get the RS-232 data to TTL levels to read into the Arduino.
Then you will start seeing stuff like this:
$SDDPT,1.7,0.0,*7D
that means it is 1.7 units (can be set to feet, meters or fathoms) deep. But calling it depth is an assumption - it is assumed you pointed the transducer down. But sound waves are unaffected by gravity - you can point it any way you want. What it actually means is that at that distance in the direction it is pointed, something caused a significant amount of sound to echo back.
ultrasonic sensors that could be waterproofed
Since this is for a sub, you need "pressure-proofed", not just waterproofed. The Maxbotix sensors are rated "IP67", which means it won't fry if you drop it in a shallow (up to 1m) stream.
That doesn't necessarily mean they'll work properly underwater: it's entirely possible that the sensor will wind up measuring the distance to the water pressing on the waterproofing, instead of sending a pulse out into the water. You need to research this.
Ran's post reminded me of one important thing about my suggestion (which is a loose description of my actual implementation) - you probably want to get a "transom mount" transducer if you get a depth finder. They are designed to be totally immersed during use. A "through hull" transducer can work, but you will need a fair amount of internal room for it and a good spot on your hull for mounting, plus you won't be able to adjust how it is aimed easily.
Hey, sorry for not replying sooner everyone, I have been away over christmas and only just returned.
Some great stuff though thanks all.
I am now adapting it to be a Hydophone effectively as I don not (at this stage need true SONAR. I am using two Panasonic WM-61A electret microphones (did consider the Piezo's - Jackrae) that are being housed within a PVC waste trap (look under the sink - you'll see what I mean) which provides the perfect housing.
The frequency bandwidht for the WM-61A is 20 - 20000Hz and I need to pick up a PING at 12kHz which I intend to pin-point using an active filter and then amplify and then send through a PIC microcontroller ADC to act upon. I am using two WM-61A's as I need to have some sort of direction differentiation when detecting the PING.
Hopefully it will all work 
At some point I need to either look at doing something directional like you are or add some wider cone transducers to the sides with some switches to go between them. The time it would take to switch between 3 transducers and get a reading might make that unworkable though. The narrow cone depth finder I am using now is mostly protection for the prototype - don't beach it at high speed.
Transducers are usually fairly narrow beam so I doubt anything with more than 20 degrees of separation between a pair of transducers would give a reliable range and direction detection and even if you got a double echo the reliability of the calculation of direction might be questionable.
An option might be to build a system for rotating the transducer head assembly, rather like a radar scanner. This would then rotate the transmission and echo beam through 360 degrees so you could "look" and "see" in all directions with only a single head. By feeding your circuit with information of rotational position you get both distance and direction of any obstructions.
All the transmission and receiver electronics could be housed within the rotational member with only the necessary power supply running through slip rings. The "coded" data generated by your electronics could be transmitted wirelessly via a low power RF system into the main control system so avoiding the necessity to transmit data via a slip-ring assembly.
jack
That still leaves me with my timing problem. I may be moving at a pretty good clip sometimes and taking a couple of seconds or more to get info could prove catastrophic.
Who's thread is this ? It seems to have been high-jacked
Who's thread is this ? It seems to have been high-jacked
Not purposefully. I answered with what I am doing and then he came back and posted the better (IMO) answer he has since found so I was following up with the OP when you offered some additional (and welcome) information.